HIV/AIDS-related Expectatons and Rsky Sexual Behavor n Malaw Adelne Delavande Unversty of Essex and RAND Corporaton Hans-Peter Kohler Unversty of Pennsylvanna January 202 Abstract We use probablstc expectatons data elcted from survey respondents n rural Malaw to nvestgate how rsky sexual behavor may be nfluenced by ndvduals survval expectatons, whch n turn depend on the perceved mpact of HIV/AIDS on survval; expectatons about own and partner s HIV status; and expectatons about HIV transmsson rates. We fnd that subjectve expectatons play an mportant role n determnng the decson to have multple sexual partners. Usng our estmated parameters, we smulate the mpact of varous polces that would nfluence expectatons. An nformaton campagn on mortalty rsk would decrease rsky sexual behavor, whle an nformaton campagn on HIV transmsson rsks, whch tend to be overestmated by respondents, would actually ncrease rsky behavor. Also, the expanson of ant-retrovral therapy (ART) treatments to all ndvduals sck wth AIDS would ncrease rsky sexual behavor among HIV-negatve ndvduals or those who have not been tested because ndvduals are aware that ART ncreases lfe expectancy, and thus reduces the cost of becomng HIV-postve. We would lke to thank Charles Bellemare, Ilyan Georgev, Alberto Holly, Erk Mejer, Chuck Mansk, Olver Sterck and Lus Vasconcelos for comments. We thank semnar partcpants at the 2009 Choce Symposum, the 20 Dauphne Workshop on Recent Advances on the Role of Belefs n Decson Theory, DIW Berln, the Faculdade de Economa da Unversdade do Porto, the Federal Reserve Bank of New York, RAND Corporaton, the School of Economcs and Management of the Techncal Unversty of Lsbon, the department of Economcs of the Unversty of Essex, and the Insttute for Socal & Economc Research of the Unversty of Essex for comments. Support for ths research through the Natonal Insttute of Chld Health and Development (grant number R03HD058976) and Nova Forum s gratefully acknowledged.
. Introducton Sub-Saharan Afrca (SSA) s the regon of the world most affected by the HIV/AIDS epdemc. It accounts for over two thrds of all people nfected worldwde, wth adult prevalence rates reachng above 25% n some countres (UNAIDS, 2009). Heterosexual ntercourse s the most common pathway of nfecton n the regon. Whle there s a growng emphass on bomedcal nterventons to prevent HIV nfectons or mprove the health of HIV-postve ndvduals, nterventons targeted at behavoral change reman an essental part of the HIV/AIDS preventon strategy, especally n poor countres (UNAIDS 200). To effectvely change rsky sexual behavor, t s mportant to understand why ndvduals who lve n hgh- HIV-prevalence envronments engage n those behavors. There are several non-mutually exclusve explanatons that can be put forward. One explanaton may be related to preferences (e.g., ndvduals n SSA may have hgh utlty from havng multple sexual partners). Another reason may be the hgh burden of dsease and the resultng hgh levels of (non-hiv-related) mortalty. Oster (forthcomng) and Phlpson and Posner (993), for example, argue that ndvduals have lttle motvaton to adopt rsk-preventon strateges, as these strateges are costly n terms of fnancal expenses (e.g., purchasng condoms) or foregone pleasures (e.g., lower levels of satsfacton as a result of gvng up extra-martal partners), but provde only lmted gans n terms of longer lfe expectancy. Another reason may be that ndvduals have msperceptons about ther current HIV status, transmsson rates or the HIV prevalence n ther communty. Wth data on behavor only, explanatons based on preferences and those based on belefs cannot be dscrmnated, thereby lmtng the ablty to devse effectve behavoral nterventons. In ths paper, we use very rch data on probablstc belefs that we collected drectly from rural Malaw survey respondents to nvestgate the role of HIV/AIDS-related expectatons on the decson to engage n rsky sex (n our case havng multple sexual partners), and smulate the mpact of varous polces on rsky behavor. We develop a smple, though qute general, twoperod theoretcal framework whch hghlghts the role of expectatons n the decson to engage n rsky sexual behavor. Our framework shows that the dfference n subjectve survval probablty assocated wth havng rsky sex versus havng safe sex s crucal for decsonmakng. It also shows that ths dfference n probablty depends n turn on a set of 6 subjectve expectatons: () expectatons of survval condtonal on beng healthy, () expectatons of 2
survval condtonal on beng nfected, () expectatons about own HIV status, (v) expectatons about partners HIV status, (v) expectatons about HIV transmsson rate assocated wth safe sex and (v) that assocated wth rsky sex. A unque feature of ths paper s that we have data on all those expectatons that are potentally relevant for behavor. We use those expectatons data and data on sexual behavor to estmate our model. We fnd that the dfference n subjectve survval probablty assocated wth havng multple sexual partners versus havng one partner play an mportant role n determnng the decson to have multple sexual partners. Ths suggests that () ndvduals n rural Malaw are forward-lookng and take nto account mortalty rsk when makng health-related choce, () expectatons data are useful to understand rsk-takng behavor n the SSA context, and () changng ndvdual belefs may be one way to change rsky sexual behavor. Usng our estmated preference parameters, we smulate the mpact of varous polces that would nfluence ndvdual expectatons. We fnd that an nformaton campagn on HIV transmsson rsks, leadng people to revse ther subjectve belefs to statstcs from medcal studes, would have a perverse effect and ncrease the probablty of havng multple partners from 20.2% to 24.6% for men and from 2.% to 4.0% for women. Ths s because respondents wdely over-estmate the relatve mpact of havng multple partners on the average probablty of becomng nfected wth HIV compared to havng one partner. However, provdng nformaton on the mortalty rsk of someone healthy and of someone nfected wth AIDS, leadng people to revse ther belefs to avalable statstcs from lfe tables, would have a postve mpact and decrease the average probablty of havng multple partners to 9.3% for men and 2.% for women. Ths s because ndvduals under-estmate the magntude of the negatve mpact of HIV/AIDS on survval. To our knowledge, provdng nformaton on mortalty rsk has never been mplemented and may be a new avenue for campagn. Also, we nvestgate the mpact of the expanson of ant-retrovral therapy treatments (ART) to all ndvduals sck wth AIDS. Whle ths s a medcal nterventon targeted to nfected people, t may have repercusson on everyone s sexual behavor. In partcular, t could change belefs about mortalty rsk f nfected. We fnd that such an expanson would ncrease the probablty of havng multple Among HIV-postve ndvduals, Lakdawalla et al. (2006) fnd that the ntroducton of ART ncreases sexual actvty n the U.S. whle Goldsten et al. (200) fnd that enrollment n AIDS treatment programs ncreases the frequency of sex but also condom use n Kenya. 3
sexual partners among HIV-negatve ndvduals or those who have not been tested from 20.3% to 2.5% for men and from 2.3% to 2.7% for women. Because ndvduals are aware that ART ncreases lfe expectancy, unversal treatment reduces the perceved cost of becomng HIVpostve. Whle subjectve expectatons have been ncreasngly asked of survey respondents n developed countres n the last 20 years, the elctaton of probablstc expectatons n developng countres s recent. Delavande et al. (20) revew the exstng evdence and conclude that collectng expectatons data n developng countres s both feasble and valuable. 2 In ths paper, we use data on probablstc expectatons about a wde range of events that we have collected as part of the 2006 wave of the Malaw Longtudnal Study of Famles and Health (MLSFH, formerly the Malaw Dffuson and Ideatonal Change Project) coverng more than 3,000 adult respondents n rural Malaw. In Delavande and Kohler (2009), we fnd that respondents provde meanngful expectatons n probablstc format accordng to varous crtera: most respondents provde probabltes that are consstent wth basc propertes of probablty theory, the subjectve expectatons are systematcally correlated wth observable characterstcs (such as gender, age, educaton, and regon of resdence) n the same way that actual outcomes vary wth these varables, and expectatons about future events vary across ndvduals n the same way as ndvduals past experence does. Yet, respondents exhbt a lot of heterogenety n expectatons. The advantage of usng expectatons data n emprcal work s that t mtgates a basc dentfcaton problem that researchers face when usng data on choces only: observed choces may be consstent wth many combnatons of expectatons and preferences. Although expectaton data are becomng avalable, only a lmted number of studes have untl now employed them to draw nferences on behavor. Recent studes ncorporatng expectatons nto econometrc models have addressed varous decsons such as contracepton choce (Delavande, 2008a), portfolo allocaton (Delavande and Rohwedder, 20, Kezd and Wlls, 2009), fertlty and sexual behavor (Shapra, 200: de Paula et al., 20), college major (Zafar, 2009, Arcdacono et al., forthcomng), teacher career (van der Klaauw, forthcomng), commttng a crme (Lochner, 2007), mgraton (McKenze et al. 2007), strateges n games (Nyarko and 2 See Mansk (2004) and Hurd (2009) for a revew of the lterature on expectatons n developed countres. 4
Schotter, 2002, Bellemare et al., 2008), and the tmng of Socal Securty clamng and retrement (van der Klaauw and Wolpn, 2008, Hurd et al., 2004). We contrbute to ths lne of work that combnes choce data wth data on subjectve expectatons to draw nferences on preferences. We do ths n the context of the HIV/AIDS epdemc n SSA. Due to potental endogenety ssues, t s challengng n many emprcal applcatons to evaluate how expectatons of events over whch ndvduals have some control causally affect ther decsons: Unobservable characterstcs may nfluence both the formaton of expectatons and decson-makng. Few papers usng expectatons data have addressed the endogenety ssue drectly (see dscusson n van der Klaauw, forthcomng). 3 We deal wth the potental endogenety arsng from the dependence of expectatons on past behavor by estmatng a recursve system of equatons: belefs about current HIV status depend on past sexual behavor and observable characterstcs, the decson to get tested for HIV s explctly estmated, and the decson to engage n rsky sexual behavor depends on ndvdual HIV/AIDS-related expectatons. Our paper bulds on several studes that have analyzed the the mpact of the belef about one sngle HIV/AIDS-related event on sexual behavor n SSA. De Paula et al. (20) for example evaluate the mpact of belefs about own HIV status on the lkelhood of engagng n rsky behavor usng data from the MLSFH. They fnd that downward revsons n belefs of beng HIV-postve ncrease rsky behavor. Unlke them, Gong (200) fnds that, n the Tanzanan and Kenyan context, ndvduals who beleved to be at low rsk of nfecton have an ncreased lkelhood of contractng a sexually transmtted dseases (STD), ndcatng rsker sexual behavor, after a postve HIV test, whle the reverse s true for those who are surprsed by a negatve HIV test. 4 Wthout usng changes n belefs about own HIV status drectly, several papers have also looked at the causal mpact of learnng one s HIV status on subsequent sexual behavor (Thornton, 2008; Delavande and Kohler, forthcomng). Few papers have assessed the role of belefs about transmsson rsks on sexual behavor 3 De Paula et al. (20) use a panel data estmator whch accommodates unobserved heterogenety as well as belef endogenety arsng from the dependence of current belefs on lagged behavors, Lochner (2007) uses fxed-effect nstrumental-varable estmates, and Bellemare et al. (2008) model preferences and belefs jontly to address the endogenety ssue. 4 In the US context, Boozer and Phlpson (2000) fnd that ndvduals who are surprsed by a HIV test results change ther behavor more. 5
(Meekers and Klen, 2002; Lammers et al., 20). Sterck (200) documents a large overestmaton of HIV transmsson rsks among students n Burund and develop a behavoral model yeldng a U-shaped relatonshp between rsky behavor and expected transmsson rsk. We are not aware of any study lookng drectly at the mpact of belefs about mortalty rsk on sexual behavor. Indrectly but related to ths, Oster (forthcomng) fnds that hgh rate of non-hiv mortalty decreases the change n sexual behavor due to an ncrease n HIV prevalence n SSA. We argue that belefs about all those events are lkely to be crucal to the decson to engage n rsky sex and therefore ought to be consdered jontly n emprcal work. We therefore complement and mprove from the current lterature by evaluatng the mpact of sexual behavor on belefs about own and partner s HIV status, transmsson rsks (condtonal on havng a safe and a rsky behavor) and mortalty rsk (condtonal on beng nfected and on beng healthy). Ths allows us to evaluate how a wde range of polces such as nformaton campagns on mortalty rsks and on transmsson rsks, and the roll-out of ART affect rsky sexual behavor. The paper proceeds as follows. Secton 2 presents the theoretcal framework that motvates the emprcal analyss. Secton 3 descrbes the data. Secton 4 presents the econometrc specfcaton and Secton 5 the analytcal sample. Secton 6 analyzes the role of subjectve expectatons n the decson to engage n rsky sex and consders a seres of robustness checks such as msreportng of sexual behavor or HIV testng outsde the MLSFH surveys. Secton 7 presents the polcy smulaton results. 2. Theoretcal framework Consder a sexually actve ndvdual who has two perods left to lve (perod and perod 2). In perod, she can choose between 2 dfferent actons: a = 0, havng sex wth one partner only; a =, havng sex wth multple partners. Her perod utlty depends on the mmedate utlty from sex V ( a ) assocated wth acton a. Indvdual can enjoy perod 2 utltyu only f she survves to perod 2. The subjectve probablty of survval to perod 2 depends on whether the ndvdual beleves that she wll be nfected at the end of perod. She may beleve that she was already nfected wth HIV before perod or that she can contract HIV durng perod. The subjectve probablty s therefore a functon of the acton taken n perod (snce perod acton may nfluence HIV status) and her subjectve belefs f of beng nfected wth HIV at the 6
begnnng of perod. In partcular, f the ndvdual beleves that she s not nfected wth HIV at the begnnng of perod (.e., f =0), the subjectve probablty of survvng to perod 2 f the ndvdual takes acton a n perod s gven by: ( ) p a S + p a S, HIV + HIV + HIV + HIV ( ) ( ) where p HIV + ( a ) s ndvdual s subjectve probablty of becomng HIV+ f she engages n acton a, HIV S + s s subjectve probablty of survvng to perod 2 f she contracts HIV n perod, and HIV S s s subjectve probablty of survvng to perod 2 f she does not contract HIV n perod. So overall, the subjectve probablty of survvng to perod 2 for an ndvdual whose subjectve probablty of beng nfected wth HIV at the begnnng of perod s f s gven by: ( ( ) ) f S + ( f ) p ( a ) S + p ( a ) S HIV + HIV + HIV + HIV + HIV We further assume that the utlty functon depends on a random term ε that s unobservable a to the econometrcan and captures heterogenety n tastes. Indvdual chooses the acton maxmzes her lfetme subjectve expected utlty,.e., she solves the followng problem: a HIV ( ( )) + HIV + HIV + HIV + HIV max V ( a ) + f S + ( f ) p ( a ) S + p ( a ) S U + ε ( ) { 0,} a a that Overall, a rsker sexual behavor may ncrease the drect pleasure from sex n perod but decreases the (subjectve) probablty of survvng to perod 2 and therefore of enjoyng perod 2 utlty. 5 3. The data: Malaw Longtudnal Study of Famles and Health (MLSFH) The analyses n ths paper are based on the 2006 and 2008 waves of the MLSFH. 6 The 5 Note that the specfcaton of the utlty functon does not allow for consderaton of altrusm. One possblty s to assume that a spouse s survval would provde utlty to an ndvdual. If the belef about transmsson of HIV wthn couples s hgh whch s the case n our data- and the survval belefs for spouses are smlar, then the probablty that the spouse survves s smlar to the ndvdual s own survval probablty. U would then capture second-perod drect utlty and the utlty from havng the spouse alve. 6 Detaled descrptons of MLSFH sample selecton, data collecton, and data qualty are provded on the project webste at http://www.malaw.pop.upenn.edu, n a Specal Collecton of the onlne journal Demographc Research 7
MLSFH s a panel survey started n 998 that collects data n three regons of rural Malaw: Balaka, Mchnj and Rumph. Balaka dstrct s located n the Southern Regon of Malaw, prmarly nhabted by Yao-speakng ndvduals and s predomnantly Muslm. Mchnj dstrct s located n the Central Regon near the border wth Zamba. It s prmarly nhabted by Chewaspeakng ndvduals, wth almost equal proportons of Catholcs and Protestants. Rumph dstrct n the Northern Regon of the country s nhabted prmarly by Tumbuka-speakng ndvduals who are predomnantly Protestant (Trntapol and Regnerus, 2006). In 2006, the MLSFH ncluded more than 3,200 male and female respondents aged 7 to 60 who were asked about a wde range of demographc, health, and soco-economc characterstcs. In 2008, slghtly more than 4,000 respondents were ntervewed, wth the addtonal respondents resultng prmarly from a new parent sample that extended the age range from 7 to 92 years by also ntervewng parents of earler MLSFH respondents. Comparsons wth the Malaw Demographc and Health Survey showed that the 2006 MLSFH sample populaton s reasonably representatve of the rural Malaw populaton (Anglewcz et al., 2007). An nnovaton of the 2006 and 2008 waves was the ncluson of an nteractve elctaton technque for subjectve expectatons that was based on askng respondents to allocate up to ten beans on a plate to express the lkelhood that an event wll be realzed (Delavande and Kohler, 2009). 7 Intervewers ntroduced the nteractve elctaton technque wth a short ntroducton (see Appendx B). After any clarfyng questons, respondents were frst asked a tranng queston about the probablty of wnnng n a local board game (Bawo), followed by a seres of expectatons questons related to economc and health outcomes. They were n partcular asked about the probablty that they are currently nfected wth HIV, that ther spouse/partner s nfected wth HIV, and ther one-year, 5-year, and 0-year mortalty expectatons. In addton to these questons about ther own mortalty, the questonnare also ncluded several questons about the one-year, 5-year, and 0-year mortalty of the followng hypothetcal ndvduals: () a woman/man of the respondent s age who s healthy and does not have HIV; () a woman/man of the respondent s age who s sck wth AIDS; () a woman/man of the respondent s age who s that s devoted to the MLSFH (Watkns et al. 2003), and n a recent workng paper that ncorporates the 2004 and 2006 MLSFH data (Anglewcz et al. 2007). 7 In 2008, the expectaton module was admnstered to all respondents who had been ntervewed n 2006, and to new respondents below the age of 60. 8
sck wth AIDS and s treated wth Antretrovral Therapy (ART). The gender used n the scenaros was the same as that of the respondent. Respondents were also asked the probablty that someone of the same gender who was currently healthy would become nfected wth HIV n the next 2 months f she (a) s marred to an HIV-postve spouse, or (b) has several sexual partners n addton to her spouse. Respondents were also asked ther percepton of the vllage HIV prevalence (from 0 to 0). The mortalty questons were desgned to ensure that respondents provded answers that would allow us to construct well-defned survval curves. In partcular, respondents were frst asked to pck the number of beans that reflects how lkely t s that they wll de wthn a oneyear perod begnnng that day. Then, wth the beans of the prevous queston stll on the plate, they were asked to add more beans to reflect how lkely t s that they would de wthn a fveyear perod. The same procedure was followed for the ten-year-perod mortalty queston. Ths ensured that respondents provded weakly ncreasng answers when the tme horzon ncreased. Delavande and Kohler (2009) provde a detaled analyss and evaluaton of the probablstc expectatons collected usng the above nteractve elctaton technque. Key fndngs from the 2006 data nclude these: (a) About 99% of the respondents are found to provde belefs consstent wth basc propertes of probablty theory when asked about nested events; (b) n bascally all the consdered domans, subjectve belefs vary consderably across ndvduals; (c) subjectve expectatons are systematcally correlated wth observable characterstcs such as gender, age, educaton, and regon of resdence n the same way that actual outcomes vary wth these varables (e.g., expectatons about nfant mortalty exhbt regonal dfferences that are smlar to actual outcomes, and expectatons about economc outcomes vary wth soco-economc status n the expected drectons); and (d) expectatons about future events vary across ndvduals n the same way as ndvduals past experence does. Another nnovatve aspect of the MLSFH s the collecton of HIV status. As part of a randomzed experment to study the determnants of HIV testng uptake, respondents were offered a free HIV test at the end of the 2004 ntervew (Thornton, 2008). At the tme of testng, respondents were gven randomly assgned vouchers redeemable for a sum of money equvalent on average to a day s wage (agrcultural labor) upon pckng up ther HIV test results at local clncs a couple of months after testng. Thornton (2008) fnds that learnng one s HIV results 9
was hghly responsve to the fnancal ncentves. 8 In 2006 and 2008, respondents were re-vsted by nurses shortly after completng the ntervew and were offered a free at-home HIV test wth mmedate results. There was no fnancal ncentve provded n 2006 and 2008 for learnng one s HIV status. In 2006, 93% of the respondents agreed to be tested and 98% of those who were tested learned ther HIV status. Overall, 5.2% were HIV-postve. Ffteen percent of the sample was not found by the team of nurses at the second vst, and were therefore not offered a test. Fnally, the questonnare asks several questons about sexual behavor. Of partcular nterest to ths paper s the number of sexual partners n the last 2 months, asked n 2008. 9 Fgure shows the mportant aspects of the tmelne of the data collecton. 4. Econometrc specfcaton Based on secton 2, the probablty of choosng multple sexual partners s the probablty that acton a = yelds hgher expected subjectve utlty than the acton a = 0,.e.: P a ( ) = = HIV + HIV + HIV + HIV + HIV ( ( ( ) )) HIV HIV HIV HIV HIV ( ) V () + f S + ( f ) p () S + p () S U + ε P + + + + V (0) + ( f S + ( f )( p (0) S + p (0) S )) U + ε0. ( ε 0 ε () (0) ) = P V V + PU, () HIV + HIV + HIV + HIV where P ( f )( p () p (0))( S S ) =. We seek to draw nferences on the structural preference parameter U to evaluate whether subjectve belefs are mportant for decson-makng. In partcular, we want to evaluate whether ndvduals are forward-lookng and take nto account relatve survval rsk when makng 8 In 2004, 9% of the respondents agreed to be tested and among those, 69% went to pck up ther test result. 9 We focus on the number of partners, abstractng from condom use, for several reasons. Frst, respondents were not asked about condom use n 2008. Second, condoms are relatvely nfrequently used n Malaw, especally n regular relatonshps (Chmbr, 2007) so the number of sexual partners s lkely to be the most mportant margn of behavoral adjustment. Thrd, women may have lmted decson power regardng the use of condom. 0
decsons. The varable P s the dfference n probablty of survval between havng multple partners (acton ) and havng one partner (acton 0). The estmate of U s gven by the coeffcent assocated wth P. We use belefs elcted n 2006 to explan sexual behavor that occurs between 2006 and 2008 (see Fgure ). The tmng s mportant because sexual behavor may lead ndvduals to revse ther belefs (e.g., about current HIV status) subsequently. Therefore, t s crtcal to use belefs elcted pror to the decson to engage n rsky behavor. Yet, there may stll be some ssues n the estmaton of equaton () due to potental endogenety of belefs arsng from the dependence of current belefs on past behavors. Unobserved heterogenety capturng tmenvarant preferences for the number of partners or the search cost of havng multple partners may be correlated wth the belefs f, f for example, belefs at the begnnng of perod depend on the pror number of partners, or f ths unobserved heterogenety also nfluences the decson to get tested for HIV. To deal wth ths ssue, we estmate a three-equaton recursve model. The frst equaton models the probablty 0 f of beng nfected wth HIV pror to the 2006 HIV test. It s a reducedform equaton whch depends on observable exogenous characterstcs and lagged sexual behavor. The second equaton models the decson to get tested for HIV n 2006. The propensty to get tested depends on demographc characterstcs X 3, on the probablty 0 f of beng nfected wth HIV pror to the 2006 HIV test, and on sexual behavor pror to the HIV test. The thrd equaton models the propensty to have multple partners. As defned n equaton (), t wll depend on demographc characterstcs and lagged sexual behavor (under the assumpton that V () V (0) β X = ), on the dfference n survval expectatons the potentally endogenous post-test belefs P, whch n turn depends on f (whch are equal to the pre-test belefs 0 f f a respondent dd not get tested for HIV n 2006 or to the actual 2006 HIV status f the respondent got tested for HIV n 2006) and the exogenous belefs ( HIV + () HIV + (0))( HIV + HIV p p S S ) The system of equatons (2) s recursve and gven by:. f = β X + u 0 3 3 3 test = β X + θ f + u (2) * 0 2 2 2
(( )( HIV + HIV + )( HIV + HIV )) a * = β X + ω f p () p (0) S S + u Where u 0 r2 r3 D u2 ~ N 0, r2 r23 u 3 0 r3 r23 r 33 test > = * f test 0 * 0 f test 0 a > = 0 otherwse * f a 0 Identfcaton requres at least one varable n X 3 not ncluded n X 2 (Maddala, 983). Note that the system s logcally consstent (Maddala 983, Wlde 200). We wll estmate the system of equatons (2) by maxmum lkelhood. 0 5. Analytc sample and defnton of the varables 5.. Analytc sample We restrct our analyss to respondents sexually actve n the 2 months pror to the survey. We also exclude 202 men who are n a polygamous marrage and have therefore multple sexual partners wthn marrage. Note that dfferent samples are used to estmate the varous equatons of the system (2). Snce X 2 and X 3 nclude lagged sexual behavor, the sample for estmatng the frst two equatons s restrcted to respondents who were sexually actve n 2006 (ndependently of whether they were ntervewed n 2008). Eghty-eght percent of the 3,240 2006 MLSFH respondents report havng at least one sexual partner n the precedng 2 months. For the thrd equaton of system (2), we focus on respondents who were sexually actve n both 2006 and 2008. Table presents basc characterstcs of the respondents who were 0 We use the cmp Stata command developed by Roodman (2009). We focus on respondents who ever had sex because the ntaton of sexual actvty may be dfferent from the decsons we study. 2
sexually actve n 2006, excludng men n a polygamous marrage. Our emprcal strategy reles on estmatng whether sexual behavor n the last 2 months reported n 2008 s nfluenced by elcted belefs reported n 2006. However, 23% of the 2006 respondents could not be resurveyed n 2008, so ther behavor cannot be used to nfer U. Note that those respondents are however used n the regressons determnng belefs formaton and testng decsons snce those rely exclusvely on varables elcted n 2006. We nvestgate whether the probablty of attrton between 2006 and 2008 s assocated wth 2006 belefs and 2006 sexual behavor (Table A) and fnd that the dfference n probablty of survval P and past sexual behavor are not correlated wth the probablty of attrton. 5.2. Defnton of varables We descrbe the dependent varables n the system of equatons (2). Table 2 presents ther descrptve statstcs. - 2006 pre-test probablty of beng currently nfected wth HIV. The varable 0 f s the respondent s answer about the lkelhood of beng currently nfected wth HIV, elcted n 2006 (and re-scaled from zero to by dvdng the number of beans by 0). The average belef s 0.. However, the dstrbuton s skewed: 66 percent of the respondents report a probablty of zero of beng currently nfected wth HIV. - HIV testng. We defne the varable test = f the respondent learned hs HIV status at the end of the 2006 ntervew, and 0 otherwse. Respondents who dd not learn ther status nclude respondents who dd not get tested because the nurses dd not fnd them or because they refused to be tested, and respondents who got tested but dd not want to learn ther status. Overall, 78 percent of our analytcal sample learned ther HIV status n 2006. - Havng multple partners n 2008. The varable a s equal to f the respondent reports n 2008 havng had more than sexual partner n the last 2 months, and zero f the respondent reports havng had only one sexual partner n the last 2 months. Table 2 shows that among respondents who were sexually actve n both 2008 and 2006, 0 percent had more than one sexual partner. Note however that there s a large dfference by gender: ths percentage s 2 percent among males compared to 2 percent among females. Because 90% of our sample s marred, the vast majorty of those multple partners refer to concurrent relatonshps. 3
We now descrbe how we compute the ndvdual-specfc dfference n survval probablty assocated wth havng multple partners and havng one partner ( HIV + )( () HIV + (0) HIV + HIV )( ) P = f p p S S. Table 3 presents the descrptve statstcs of the varous relevant expectatons for respondents who were sexually actve n 2006 and 2008. - 2006 post-test probablty of beng currently nfected wth HIV, f as follows: f. We defne the varable f = 0 f the respondent learned that s/he was HIV-negatve n 2006 HIV test f the respondent learned that s/he was HIV-postve n 2006 HIV test 0 f f the respondent dd not learn hs/her HIV status n 2006 The underlyng assumpton s that ndvduals revsed ther belef upon learnng ther HIV status accordng to the test result. 2 Table 3 shows that the average belef s equal to 0.05 and s thus lower than the pre-test belef, due to the fact that a large number of respondents who were tested found out that they were HIV-negatve. - Survval expectatons, HIV S + and HIV S. We use the 2006 elcted 0-year mortalty rate condtonal on beng nfected wth AIDS to determne HIV S + and the 2006 elcted 0-year mortalty rate condtonal on beng currently healthy to determne HIV S. 3,4 Table 3 shows 2 There s no emprcal evdence on how people revse ther belefs just after learnng ther test results. In Delavande and Kohler (forthcomng), we report that about two-thrds of respondents who learn they were HIV-negatve n 2004 allocated zero beans when asked ther belefs of nfecton n 2006. Because ndvduals may have subsequently engaged n rsky behavor, ths pattern n the data s consstent wth our current updatng assumpton. More surprsngly, only 0% of the respondents who were told they were HIV-postve n 2004 provded 0 beans n response to the queston about ther subjectve probablty of beng nfected wth HIV n 2006. Delavande and Kohler (forthcomng) speculate on varous explanatons: () respondents may have beleved the test result at frst, but have forgotten about t or reassessed ther status as tme elapsed, specfcally f they had contnued to feel farly healthy; and () respondents may actually beleve that they are HIV-postve, but were embarrassed to acknowledge t vs-à-vs the ntervewer durng the 2006 survey. Several results lead us to beleve that embarrassment may be an ssue: respondents are more lkely to report zero beans n places wth more HIV-related stgma, and learnng a HIVpostve status lead to a change n behavoral changes that reduce the HIV nfecton rsk to others, suggestng an underlyng change n belefs about HIV status. 3 We use the survval probablty condtonal on beng nfected wth AIDS because people tend to thnk that the duraton from nfecton to AIDS symptoms s much shorter than t s (Santow et al. 2008). 4
that on average respondents thnk that there s a 4 percent chance of beng alve n 0 years condtonal on beng healthy, compared to only a percent chance of beng alve n 0 years condtonal on beng nfected wth AIDS. Ths shows that ndvduals are aware that beng nfected wth HIV/AIDS reduce lfe expectancy n the long run. Table A2 n the appendx show the average survval belefs by age group for someone healthy, nfected wth AIDS, and nfected wth AIDS but treated wth ant-retrovral therapy (ART). It shows a gradent of survval expectatons by age: younger people expect to lve longer. It also shows that for all age groups, ndvduals are aware that beng nfected wth AIDS wll shorten lfe expectancy substantally, and that beng on ART wll mtgate ths. HIV + - Subjectve probablty of nfecton assocated wth havng multple partners, (). We use the 2006 elcted expectatons about the lkelhood that a hypothetcal ndvdual of the respondent s gender would become nfected wth HIV n the next 2 months f s/he was havng several sexual partners n addton to a spouse. Respondents beleve on average that there s an 8 percent chance of becomng nfected wth HIV condtonal on havng multple partners (Table 3). HIV + - Subjectve probablty of nfecton assocated wth havng one partner, (0). Ths probablty s agan ndvdual-specfc and depends on respondents belef about the status of p p ther man partner. It s defned as p (0) = Π f, where HIV + HIV + p Π s person s HIV + perceved lkelhood of becomng nfected wth HIV durng the next 2 months for someone who s marred to an HIV+ ndvdual and f p s s subjectve belefs about her partner s HIV status after the 2006 HIV test and before engagng n acton a. Note that a respondent may not know the test result of her spouse f the latter dd not share the results. We assume that a respondent learned the status of her spouse after the 2006 HIV test f, n 2008, she reports that the last tme her spouse got tested, he shared hs test results wth her, and f the last tme occurred durng the 2006 MLSFH data collecton perod. So we defne follows: f p as 4 Wth respect to the model, the defnton of the survval probablty varables mples that our emprcal analyss focuses on the followng trade-off: drect utlty from sex now versus hgher chance of survval n 0 years. Ideally, one would analyze a model wth more than two perods, but we do not have the data to estmate t. We thus focus on a tme-frame n whch there are large dfferences n survval by HIV status. 5
0 f the spouse learned that s/he was HIV-negatve n the 2006 HIV test and the respondent reports that the spouse shared test results f the spouse learned that s/he was HIV-postve n the 2006 HIV test and the respondent reports that the spouse shared test results f p = 2006 elcted belefs about current nfecton status Belefs about vllage prevalence f the spouse dd not learn hs/her HIV status n 2006 or the respondent reports that the spouse dd not share f the respondent dd not report havng a man partner n 2006 Respondents beleve on average that there s a 93 percent chance of becomng nfected wth HIV wthn 2 months f one s marred to an HIV-postve spouse, whle the average partner s nfecton probablty s 8 percent. Overall, the average subjectve probablty of becomng nfected wth HIV wthn 2 months, condtonal on havng sex wth one partner, s 8 percent, whch s about one-tenth the perceved chance of becomng nfected condtonal on havng multple partners. So, overall, respondents beleve that havng multple partners puts them at a substantally greater rsk of becomng nfected wth HIV. HIV + Note that our analyss used belefs regardng the transmsson of HIV () and Π p HIV + that were elcted n 2006 before respondents had the opportunty to get tested and learned ther HIV status. Potentally, upon learnng ther status, respondents could have updated not only ther belefs about ther own HIV status but also ther belefs about the transmsson of HIV assocated wth varous behavors. Ths would be problematc only for respondents who are HIV-negatve (as those transmsson rsk expectatons would not enter the decson problem of ndvduals who found out that they are HIV-postve). In Delavande and Kohler (forthcomng), we nvestgate the causal mpact of learnng HIV status n 2004 on elcted 2006 HIV/AIDS-related expectatons usng an nstrumental-varable approach. We fnd that, among HIV-negatve ndvduals, learnng one s status had no mpact on expectatons about transmsson rsk. Ths suggests that 2006 belefs about transmsson rsk are unlkely to have been revsed after the 6
2006 HIV test by respondents who found out that they were HIV-negatve. Fnally, we nclude n all equatons basc demographc characterstcs (e.g., martal status, educaton, regon) and an ndcator for whether the respondents report havng multple sexual partners n the 2006 ntervew (8% of the respondents dd, see Table ), as those are thought to nfluence sexual behavor, the testng decson, and pre-test belefs about HIV status. We also nclude ndcators for relgon, as relgon may nfluence rsky behavor and rsk perceptons (e.g., Trntapol and Regnerus, 2006). As ponted out n Secton 4, dentfcaton requres at least one varable ncluded n X 3 but not n X 2. For that varable, we used the fnancal ncentves (equal on average to 02 Kwacha, whch corresponds approxmately to a day s agrcultural labor wage) that were provded for learnng one s HIV status n 2004. The dea s that ndvduals provded wth a larger fnancal ncentve were more lkely to learn ther HIV status n 2004 (Thornton, 2008), whch would nfluence ther 2006 belefs about whether they are nfected wth HIV. However, those ncentves provded n 2004 should not nfluence the decson to get tested n 2006. Note however that 28 percent of the respondents dd not partcpate n the 2004 HIV test (Table ). Among those who were offered the test, only 9 percent refused to get tested. The other 9 percent were not elgble, not found at the tme of the 2004 HIV test or not ntervewed n 2004. We also nclude the 2006 elcted expectatons about the lkelhood that a hypothetcal ndvdual of the respondent s gender would become nfected wth HIV n the next 2 months f s/he was havng several sexual HIV + partners n addton to the spouse () and the lkelhood of becomng nfected wth HIV p durng the next 2 months for someone who s marred to an HIV+ ndvdual Π HIV + as varables that nfluence the respondent s belef about whether s/he s currently nfected wth HIV but do not nfluence the testng decson. In the HIV testng equaton, we nclude an ndcator for whether the respondents know someone on ant-retrovral therapy (ART), as ths may ncrease the motvaton to get tested. Fnally, when estmatng the propensty to have multple partners, we nclude an ndcator for whether the respondent was rated as more or much more attractve than average by the ntervewer, as t may be easer for more attractve ndvduals to fnd addtonal sex partners. Thrty-three percent of the respondents ft n that category. Attractveness and lagged sexual behavor may proxy the set of avalable partners. 7
6. Emprcal Results 6.. Estmaton of the system of equatons (2) Because men are much more lkely to have multple sexual partners, we conduct separate regressons by genders. Tables 4 and 5 present the maxmum-lkelhood estmaton results of equaton (2) for women and men respectvely. In the frst column of Tables 4 and 5, where the ndcator for havng multple partners s used as a dependent varable, we fnd that the coeffcent assocated wth the dfference n survval probablty P, whch estmates the parameter U n the utlty functon, s postve and statstcally sgnfcant at 5% for both women and men. The margnal effect on the predcted probablty s large and equal to 0.038 for women and 0.50 for men when all the varables are evaluated at the mean. Ths provdes evdence that ndvduals are forward-lookng and take nto consderaton subjectve expectatons about relatve mortalty rsk, HIV status, and transmsson rates when makng decsons related to sexual behavor. probablty Focusng on women, we can note that only beng marred and the dfference n survval P have predctve power to explan havng multple partners. For both men and women, marred respondents are less lkely to have multple partners. For men, the coeffcent assocated wth lagged sexual behavor s the largest n absolute value and statstcally sgnfcant at %. Ths shows that men who had multple partners n the past keep havng multple partners, ether because past behavor reflects heterogenety n preferences or a smaller cost for searchng for new partners. Attractve men are also more lkely to have had multple sexual partners n the last 2 months, whle Chrstans other than Catholcs and those belongng to ndgenous churches are less lkely to have had multple partners than Catholcs. The second column of Tables 4 and 5 presents the estmates for second equaton of the system (2), whch looks at the HIV testng decson. There are nterestng dfferences between men and women. Men who beleve they have a smaller probablty of beng nfected wth HIV and those who have had multple sexual partners n the past are less lkely to be tested, whle the reverse s true for women. Fnally, the thrd column of Tables 4 and 5 present the estmates for the frst equaton of system (2), whch looks at pre-hiv-test belefs about nfecton status. For both men and women, havng multple partners s assocated wth a hgher perceved probablty of beng currently nfected wth HIV. Women aged 30-39 beleve that there s a hgher chance that they are nfected 8
compared to younger women, whle men who are more than 50 years old report a lower probablty of beng nfected than men who are less than 29. The bottom panel of Tables 4 and 5 shows estmates of the varances and covarances of the random terms. For both men and women, we fnd that r 23 s statstcally sgnfcantly dfferent from zero at 5%, suggestng that there s a correlaton between the random terms of the nfecton expectaton equaton and the testng equaton. Ths estmate of the covarance s postve for men and negatve for women. However, the covarance between the random term u of the equaton estmatng the propensty to have multple sex partners and the other equatons s not statstcally sgnfcantly dfferent from zero, suggestng that, n ths context, there s no endogenety ssue when estmatng the mpact of survval expectatons on havng multple sexual partners. 6.2. Potental endogenety of the HIV transmsson expectatons Our estmaton strategy deals wth endogenety of belefs about nfecton status arsng from the dependence of current belefs on past behavors (lagged sexual behavor or HIV testng). Another concern mght be that unobservable trats also nfluence HIV transmsson expectatons as well as the decson to engage n rsky sex. For example, the HIV transmsson expectatons may depend on other behavors, such as condom use or frequency of ntercourse, whch may be related to unobservable characterstcs that also nfluence the decson of havng multple partners. Ths concern s mtgated by the fact that those expectatons are asked about hypothetcal ndvduals (see Appendx B). Yet, as a robustness check, we augment the system of equatons estmated above by two equatons predctng the transmsson rates that are relevant for the decson-makng process. We assume that the probabltes of contractng HIV condtonal on havng multple partners and condtonal on beng marred to an HIV+ spouse depends on exogenous characterstcs X 4. The system of 5 equatons we estmate s: 9
Π = β X + u HIV + 5 4 5 HIV + p () = β X + u 4 4 4 f = β X + λ p () + δπ + u 0 HIV + HIV + 3 3 3 test = β X + θ f + u * 0 2 2 2 HIV + HIV + HIV + HIV (( )( )( )) a * = β X + ω f p () p (0) S S + u u 0 r r 2 3 r4 r5 u 2 0 r2 r23 r24 r25 where D u 3 ~ N 0, r3 r23 r33 r34 r 35, u4 0 r4 r24 r34 r44 r45 u 5 r5 r25 r35 r45 r 55 and the dependent varables are defned as prevously. Identfcaton requres X 4 to nclude varables not ncluded n X 3, and X 3 to nclude varables not ncluded n X 2. We stll use the fnancal ncentves that were provded for learnng one s HIV status n 2004 and the HIV transmsson expectatons HIV + Π and () HIV + p (3) as varables ncluded n X 3 but not n X 2. We use knowledge questons about non-sexual HIV transmsson (whether the respondent knows that a pregnant woman can transmt the AIDS vrus to her unborn chld and that a woman can transmt the AIDS vrus through breast mlk) and the number of known people the respondent suspects to be sck wth AIDS as varables that nfluence the transmsson expectatons wthout drectly nfluencng the belefs about current HIV status as varable ncluded n X 4 but not n X 3. The motvaton for usng knowledge for non-sexual transmsson as excluded varable s that those are lkely correlated wth overall knowledge of HIV transmsson, ncludng sexual mode of transmsson. However, snce those belefs are about mother-to-chld transmsson, they should not drectly nfluence belefs about current HIV status once we control for belefs due to sexual transmsson. Smlarly, we expect the number of known people that the respondent suspects to be sck wth AIDS to be a proxy for the dsease envronment, therefore nfluencng transmsson rsk wthout nfluencng belefs about HIV status drectly. 5 The frst two columns of Tables 6 show the estmaton results for women and men respectvely for the equaton usng the ndcator for havng multple partners as dependent 5 Note that the correlaton between the number of known people the respondent suspects to be sck wth AIDS and the current belefs about HIV status s very low (0.07). 20
varables. Tables A3 and A4 n Appendx A show the complete estmaton results for all the equatons. As before, the coeffcent assocated wth the dfference n survval probablty, whch estmates the utlty parameter U, s postve and statstcally sgnfcant at 5% for both women and men. It s actually larger n absolute value than n the results based on the system of equatons (2). The margnal effect on the predcted probablty s large and equal to 0.045 for women and 0.60 for men when all the varables are evaluated at the mean. The coeffcents assocated wth the other ndependent varables n the equatons for havng multple partners, testng and pre-test belefs are smlar to those n the system of equatons (2). One dfference s that wth ths new specfcaton, we fnd that the HIV transmsson expectatons are predctors of belefs about current HIV status for women. Female respondents who report a hgher probablty of becomng nfected f one has several sexual partners also report a hgher probablty of beng currently nfected wth HIV. Those however who report a hgher probablty of becomng nfected f marred to an HIV+ spouse report a lower probablty of beng nfected. For both men and women, we fnd as earler that the estmates of the covarance r 23 s statstcally sgnfcantly dfferent from zero at 5%. For women, we also fnd that r 35 and r 45, whch estmate the covarances of the random terms n the subjectve probabltes, are statstcally sgnfcantly dfferent from zero at 5%. For men, only the covarance of the random terms of the two HIV transmsson expectaton equatons s statstcally sgnfcantly dfferent from zero. As before, the covarance between the random term u of the equaton estmatng the propensty to have multple sex partners and those of the other equatons s not statstcally sgnfcantly dfferent from zero, suggestng that agan there s no endogenety ssue when estmatng the mpact of survval expectatons on havng multple sexual partners. P 6.3. Robustness check: HIV testng between 2006 and 2008 So far, we have assumed that the only way to get tested was through the MLSFH survey. However, HIV testng s becomng more common n Malaw, and some respondents reported that they had been tested between the 2006 and the 2008 waves. Among respondents who were sexually actve n 2006, 2.3% of those who dd not learn ther HIV status as part of the 2006 MLSFH HIV testng report n 2008 that they have been tested for HIV between the 2006 2
ntervew and December 2007. In addton, 3.9% of those who had learned ther HIV status n 2006 also report havng been tested between the 2006 ntervew and December 2007. We therefore may have measurement error n belefs about current nfecton for those who got tested outsde of the MLSFH. To deal wth ths, we assume that the HIV status that they learned n between the 2006 MLSFH testng and December 2007 s the same as the results of the 2008 MLSFH HIV test. 6 We re-estmate the system of equaton (3) based on those assumptons. The 3 rd and 4 th columns of Table 6 presents the results of the equaton wth havng multple sexual partners as the dependent varable and shows that the results are very smlar to those of Columns and 2. 6.4. Subjectve expectatons vs. hstorcal frequences We fnd that subjectve expectatons are predctve of sexual behavor. However, one may wonder f we would get smlar results by usng objectve probabltes,.e. hstorcal frequences about transmsson rates and lfe tables. To nvestgate the value-added of collectng expectatons data, we assume that the probabltes of survval condtonal on beng healthy are as gven n the UN lfe tables for Malaw wthout AIDS (Unted Natons, 2008). We take the probabltes of survval condtonal on beng nfected as equal to those n Todd et al. (2007), who measured survval snce sero-converson based on 4 East Afrcan populaton cohort studes before the avalablty of ART (two studes n Uganda, one n Tanzana, and one n Rwanda). We also assume that the probablty of becomng nfected wth HIV wthn one year f marred to an HIV+ spouse s 5.7% for men and 0.55% for women based on Ugandan data from Carpenter et al. (999). Fnally, we assume that the probablty of becomng nfected wthn one year condtonal on havng multple partners s 0.67%, whch s half the two-year sero-converson rate between 2006 and 2008 n the MLSFH among those who report havng had multple partners n 2008. 7 Fnally, we set the vllage prevalence equal to the MLSFH regonal prevalence (whch s 6 Ths s accurate for those who tested negatve n 2008, but may potentally be a strong assumpton for those who tested postve n 2008, as some may have sero-converted after ther latest test. Among those who dd learn ther HIV status n 2006 and report beng tested after the 2006 ntervew, 5.9% tested postve n 2008 and.% refused to get tested. For the latter group (7 observatons), we use the 2006 elcted belefs about current nfected status as the belefs used for decson-makng. Among those who got tested as part of the 2006 MLSFH and got retested before December 2007, % changed sero-status and tested postve n the 2008 MLSFH. 7 Fve percent of the respondents who tested HIV-negatve n 2006 and who report havng multple partners n 2008 refused to get tested n 2008. We assume that HIV ncdence was the same among those who refused to get tested 22