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1 University of Nersk - Linoln DigitlCommons@University of Nersk - Linoln U.S. Environmentl Protetion Ageny Ppers U.S. Environmentl Protetion Ageny 1997 The Agriulturl Helth Study: Ftors Affeting Completion nd Return of Self-Administered Questionnires in Lrge Prospetive Cohort Study of Pestiide Applitors Roert Trone Ntionl Cner Institute Mihel Alvnj Ntionl Cner Institute Sheil Hor Zhm Ntionl Cner Institute Jy Luin Ntionl Cner Institute Dle Sndler Ntionl Institute of Environmentl Helth Sienes, See next pge for dditionl uthors Follow this nd dditionl works t: Prt of the Civil nd Environmentl Engineering Commons Trone, Roert; Alvnj, Mihel; Hor Zhm, Sheil; Luin, Jy; Sndler, Dle; MMster, Suznne; Rothmn, Nthniel; nd Blir, Aron, "The Agriulturl Helth Study: Ftors Affeting Completion nd Return of Self-Administered Questionnires in Lrge Prospetive Cohort Study of Pestiide Applitors" (1997). U.S. Environmentl Protetion Ageny Ppers This Artile is rought to you for free nd open ess y the U.S. Environmentl Protetion Ageny t DigitlCommons@University of Nersk - Linoln. It hs een epted for inlusion in U.S. Environmentl Protetion Ageny Ppers y n uthorized dministrtor of DigitlCommons@University of Nersk - Linoln.

2 Authors Roert Trone, Mihel Alvnj, Sheil Hor Zhm, Jy Luin, Dle Sndler, Suznne MMster, Nthniel Rothmn, nd Aron Blir This rtile is ville t DigitlCommons@University of Nersk - Linoln:

3 AMERICAN JOURNAL OF INDUSTRIAL MEDICINE 31: (1997) The Agriulturl Helth Study: Ftors Affeting Completion nd Return of Self-Administered Questionnires in Lrge Prospetive Cohort Study of Pestiide Applitors Roert E. Trone, PhD, 1 * Mihel C.R. Alvnj, DrPh, 1 Sheli Hor Zhm, SD, 1 Jy H. Luin, PhD, 1 Dle P. Sndler, PhD, 2 Suznne B. MMster, PhD, 3 Nthniel Rothmn, MD, MHS, 1 nd Aron Blir, PhD 1 Response rtes were exmined in prospetive epidemiologi study of individuls, mostly frmers, from nd seeking pestiide pplitor liense during the period from 1994 through In the first yer of enrollment 16,535 frmers (representing 77% of eligile frmer pplitors) enrolled in the study y ompleting 17-pge questionnire dministered t pestiide trining session; 47% of the enrolled frmers ompleted nd returned muh longer tke-home questionnire. The hrteristis of frmers who ompleted only the enrollment questionnire were quite similr to those of frmers who lso ompleted nd returned the tke-home questionnire. The most notle differene ws the inresed ge of responders. Thus, the study popultion might hve slightly higher umultive frm exposures nd slightly lower urrent frm exposures thn the se popultion of ll frmer pplitors. The lk of evidene for sustntil seletion is is ressuring for the Agriulturl Helth Study, nd provides mesure of ressurne for other studies depending on the voluntry ompletion of self-dministered questionnires. Am. J. Ind. Med. 31: , r 1997 Wiley-Liss, In. KEY WORDS: epidemiologi methods; prospetive ohort study; ouptionl exposure; seletion is (epidemiology); ner INTRODUCTION Enrollment of sujets into prospetive epidemiologi study is often omplished using self-dministered questionnire. Questionnires re usully miled to eligile individuls, filled out t home, nd returned y mil. In ll 1 Epidemiology nd Biosttistis Progrm, Ntionl Cner Institute, Bethesd, MD. 2 Ntionl Institute of Environmentl Helth Sienes, Reserh Tringle Prk, NC. 3 Environmentl Protetion Ageny, Reserh Tringle Prk, NC. *Correspondene to: Roert Trone, Ntionl Cner Institute, EPN 403, Bethesd, MD Aepted for pulition 1 July epidemiologi studies, some eligile individuls refuse to prtiipte, nd suh nonresponse n led to seletion is [Wholder et l., 1992]. Aordingly, there is onsiderle interest in identifying hrteristis whih distinguish responders from nonresponders in epidemiologi studies. The Agriulturl Helth Study is lrge prospetive ohort study eing onduted in nd to investigte potentil dverse helth effets of vriety of exposures relted to frming [Alvnj et l., 1996]. The impetus for the study omes from experimentl nd epidemiologil investigtions whih suggest tht some griulturl exposures my ontriute to exesses for ertin ners nd other diseses [Blir nd Zhm, 1991; Blir, 1992]. Study sujets re ll liensed pestiide pplitors, the mjority of whom re frmers, nd the spouses or domesti prtners (herefter simply spouses) of frmer r 1997 Wiley-Liss, In. This rtile is US Government work nd, s suh, is in the puli domin in the United Sttes of Ameri.

4 234 Trone et l. pplitors. Persons who pply restrited-use pestiides must undergo trining or testing in the sfe hndling of pestiides t lest every 3 yers in order to otin pestiide pplitor liense. All individuls from nd North Crolin seeking pestiide pplition liense from 1994 through 1996 will e invited to prtiipte in the Agriulturl Helth Study. Enrollment is omplished y the ompletion of self-dministered questionnire t pestiide trining or testing session. Eh frmer pplitor who ompletes n enrollment questionnire is given set of longer questionnires (one to e ompleted y the frmer nd two to e ompleted y the spouse) to e tken home, ompleted nd returned y mil. During the first yer of the 3-yer enrollment period, 16,535 frmers, representing 77% of eligile frmer pplitors, ompleted the enrollment questionnire. Although this response rte for the enrollment questionnire ompres fvorly with enrollment rtes for other lrge prospetive ohort studies [Doll nd Hill, 1964; Brton et l., 1980; Chow et l., 1992; Potter et l., 1992; Boie et l., 1995], only 47% of the enrolled frmers returned the seond, more urdensome, tke-home questionnire. In plnning how to inorporte informtion from the seond questionnire into the sttistil nlysis of disese outomes within the frmer ohort, it is importnt to determine the extent to whih nonresponders differ from responders with regrd to disese nd exposure hrteristis. In this pper, the responses from the enrollment questionnire re ompred etween those frmers who returned nd those who did not return the tke-home questionnire, in order to identify hrteristis distinguishing individuls willing to omplete t home nd return lengthy, self-dministered questionnire. Implitions for the Agriulturl Helth Study nd for other epidemiologi investigtions will e eluidted. MATERIALS AND METHODS Study Questionnires In order to motivte eligile sujets to prtiipte in the Agriulturl Helth Study, informtion on the study is presented during eh pestiide trining session. This informtion is presented y study stff in nd y griulturl extension gents in, ut the presenttion is, otherwise, the sme in oth sttes. Enrollment is hieved through return of ompleted questionnire t the end of trining session. The 17-pge enrollment questionnire seeks personl identifying informtion (i.e., nme, irth dte, Soil Seurity numer, nd ddress) for the pestiide pplitor, nd if the pplitor is mrried or living s mrried, for the spouse, in order to filitte follow-up for future helth outomes. The enrollment questionnire lso requests suffiient informtion for si nlysis of prospetively sertined helth outomes. Thus, informtion is requested regrding pplitor lifestyle nd ouptionl ftors, inluding smoking history, lohol onsumption, fruit nd vegetle onsumption, prior medil onditions, fmily history of disese, pestiide use, type of frm, nd vriety of other frm-relted tivities. The tke-home, self-dministered questionnire seeks more detiled informtion on work prties, pestiide use, pestiide pplition proedures, helth history, s well s informtion on other ouptions nd exposures, ooking prties, nd dditionl lifestyle ftors. In ddition to providing informtion not sertined through the enrollment questionnire, the tke-home questionnire llows more quntittive ssessment of vrious griulturl exposures. Applitors who report eing mrried or living s mrried re lso given two questionnires to e ompleted y their spouses nd returned y mil. These questionnires enroll the spouse in the study, verify identifying informtion provided y the pplitor on the spouse, nd seek informtion on spouse lifestyle nd environmentl exposures, inluding smoking history, lohol onsumption, ooking prties, diret nd indiret griulturl exposures, personl medil history, nd fmily history of disese. Investigtion of Nonresponse The exmintion of preditors of nonresponse will e restrited to frmers in the Agriulturl Helth Study. Thus, the popultion investigted in this pper onsists of ll frmer pplitors who enrolled in the study during the first yer. The responses to questions on the enrollment questionnire of the frmers nd frmers who returned the tke-home questionnire re ompred to the orresponding responses of those frmers who did not return the tke-home questionnire. Due to the length of the enrollment questionnire, the impt of ftors not exmined in previous studies of nonresponse (e.g., diet nd lohol use), in ddition to numer of ftors relted to frming, n e investigted. Typilly, either oth pplitor nd spouse responded in household, or neither responded, nd thus this investigtion will exmine only the tke-home questionnire response rtes for enrolled frmers. nd differ sustntilly in oth griulturl prties nd in ertin lifestyle hrteristis, nd there were minor differenes in how the study ws presented t the pestiide trining sessions in the two sttes. Aordingly, the omprison of responders nd nonresponders will e presented seprtely for eh stte. For eh question on the enrollment questionnire, the distriutions of responses for frmers who returned the tke-home questionnire were ompred to those for frmers who did not return the tke-home questionnire using the Person

5 Response in the Agriulturl Helth Study 235 hi-squre sttisti. When the response to question hd nturl ordering (e.g., numer of yers of edution or numer of hildren) hi-squre trend sttisti ws employed. When djustment for possile onfounding ws required, strtified hi-squre nlyses [Thoms nd Grt, 1983] were performed, s indited in the text or tles. Beuse of the lrge numer of questions exmined, severl signifint differenes etween responders nd nonresponders re expeted to our y hne lone. Approximtely 160 omprisons were mde in eh stte, ut mny of the responses were highly orrelted (e.g., frmers often report very similr spetrum of speifi pestiides pplied if they grow the sme rops). In n ttempt to djust, ut not overdjust, for multiple omprisons, Bonferroni djustment [Miller, 1981], ssuming 100 omprisons ws employed in eh stte, leding to ritil level of in determining the signifine of differenes y response sttus. All suh signifint findings re denoted in the tles. Conventionlly signifint (i.e., p #0.05) differenes in one stte whih support signifint findings y the more stringent riterion in the other stte, re reported in the text. RESULTS TABLE I. Age t Enrollment Distriution (Perentge) for Frmers Enrolled into the Agriulturl Helth Study Yers Q No Q Q NoQ # $ Q: Enrolled frmers who ompleted nd returned the tke-home questionnire; N 5 4,492 in nd N 5 3,362 in. No Q: Enrolled frmers who filed to omplete nd return the tke-home questionnire; N 5 4,272 in nd N 5 4,409 in. Signifint differene etween distriution for responders nd nonresponders, with p, In the first yer of the Agriulturl Helth Study, 8,764 frmers nd 7,771 frmers enrolled in the study. Of these enrollees, 4,492 (51.3%) frmers nd 3,362 (43.3%) frmers returned the tke-home questionnire. Among frmers who were mrried or living s mrried, the response rtes for the return of the spouse questionnire in nd were 51.4% nd 43.6%, respetively. Tle I ompres responders nd nonresponders y their ges t enrollment. In oth nd the responders were signifintly older thn the nonresponders. The ge differene ws sustntil; the verge ge t enrollment ws 48.3 for responders, 44.0 for nonresponders, 50.7 for responders, nd 46.1 for nonresponders. Beuse responses to mny questions in the enrollment questionnire re likely to depend on ge, ll susequent omprisons of responders nd nonresponders will e ge-djusted using strtified hi-squre nlyses, with yer of irth strtified s follows: prior to 1926, , , , , nd fter Similrly, susequent frequeny distriutions will e diretly ge-stndrdized to the ge distriution of ll enrolled study sujets in oth sttes. Distriutions of frmers y month of enrollment in the study (dt not shown) differed signifintly etween responders nd nonresponders in eh stte, with responders more likely to hve enrolled during winter months. The ge-djusted perentges of responders who enrolled from Novemer to Ferury were 84.1% in nd 64.8% in ; the omprle perentges for nonresponders were 77.4% nd 57.7% in nd, respetively. Viewed in different wy, the gedjusted response rtes for frmers enrolling in Novemer through Ferury were 52.1% in nd 52.9% in North Crolin, while for frmers enrolled in ll other months the response rtes were 41.1% in nd 45.4% in North Crolin. Thus, the higher rude response rte for return of the tke-home questionnire in (i.e., 51.3% in, ompred to 43.3% in ) is due to the ft tht signifintly higher perentge of frmers in ttended testing or trining sessions held during winter months, when there were fewer frm responsiilities. Edutionl differenes were not lrge (Tle II); the perentges of sujets with edution eyond high shool were 45.3% for responders nd 41.8% for nonresponders in, nd 42.2% for responders nd 37.1% for nonresponders in. Nonetheless, responders were more eduted in oth sttes (p in ). Mritl sttus distriutions for responders nd nonresponders showed no sustntil disordne (Tle II), ut differed signifintly in, with responders eing more likely thn nonresponders to hve never mrried nd slightly less likely to e divored. Responders in lso differed somewht from nonresponders y mritl sttus (p ), with responders gin eing slightly more likely to hve never mrried. For frmers who reported hving ever een mrried there ws tendeny for nonresponders to hve lrger fmilies in oth sttes (p in ). The perentges of mrried frmers with 3 or more hildren were 50.5% for responders nd 52.9% for nonresponders in, nd 30.7% for responders nd 33.4% for nonresponders in. Responders tended to e less likely to hve hd reent irth, ut the differene ws not signifint in either stte.

6 236 Trone et l. TABLE II. Distriution (Perentge) of Highest Edutionl Level Ahieved, Mritl Sttus, Numer of Children, nd the Birth of By Within the Pst 9 Yers for Frmers Enrolled in the Agriulturl Helth Study TABLE III. Distriution (Perentge) of Too nd Alohol Use for Frmers Enrolled in the Agriulturl Helth Study Q No Q Q NoQ Q No Q Q NoQ Highest Level of Edution 1 8 yers Some HS HS grd Beyond HS College grd Beyond College Mritl Sttus Never mrried Mrried Divored Widowed Numer of Children d $ By in Lst 9 Yers d Yes Reltive frequeny distriutions ge-djusted y diret stndrdiztion to the omined study popultion in oth sttes. Q, No Q, see Tle I. Signifint differene etween distriution for responders nd nonresponders in gestrtified nlysis, p, d Anlysis restrited to mrried frmers. Tle III ompres too nd lohol use y response sttus. Although similr perentges of responders nd nonresponders reported ever smoking igrettes, responders were more likely thn nonresponders to hve quit smoking igrettes (p in ). There were no signifint differenes etween responders nd nonresponders in the numers of igrettes smoked per dy during smoking yers, nd, lthough not shown in the tle, in the durtion of smoking igrettes or in the use of too produts other thn igrettes. Nonresponders onsumed lohol slightly more often thn responders (p in ); 22.2% of responders, 25.3% of nonresponders, 13.2% of responders, nd 15.2% of North Crolin nonresponders onsumed lohol 2 or more times Cigrette Smoking Ever smoke Quit smoking Numer of Cigrettes Per Yer # Frequeny of Alohol Consumption Never ,1 per mo per mo dy/wk dys/wk $5 dys/wk Age-djusted reltive frequeny distriutions, see Tle II. Q, No Q, see Tle I. Signifint differene, see Tle II. week. Nonresponders onsumed slightly more lohol on those osions when they drnk, ut the differenes were not sttistilly signifint in either stte (dt not shown). Tle IV presents the distriutions for frequeny of vegetle nd fruit onsumption mong enrolled frmers. Responders onsumed vegetles signifintly more often thn nonresponders in oth sttes; the perentge of individuls onsuming vegetles t lest one dy ws 48.0% for responders ompred to 42.8% for nonresponders in, nd 53.3% for responders ompred to 48.5% for nonresponders in. Responders lso te fruit more often thn nonresponders (p for ), ut the disprity etween responders nd nonresponders in fruit onsumption ws smller thn tht for vegetle onsumption. There ws no evidene of ny differenes etween responders nd nonresponders in the types of rops or livestok produed in either stte (dt not shown). The numers of res plnted in rops nd the numers of livestok tended in the pst yer re ompred in Tle V. There were inverse reltionships in oth sttes etween ge nd the numer of res plnted nd the numer of livestok tended (dt not shown). After ge-djustment there remined slight tendeny for nonresponders to e involved in lrger frming enterprises thn responders, lthough the

7 Response in the Agriulturl Helth Study 237 TABLE IV. Distriution (Perentge) of Frequeny of Vegetle nd Fruit Consumption for Frmers Enrolled in Agriulturl Helth Study TABLE V. Distriution (Perentge) of Numer of Ares Plnted in Crops nd Numer of Livestok Tended nd Durtion nd Frequeny of Personl Pestiide Applition for Frmers Enrolled in the Agriulturl Helth Study Q No Q Q NoQ Vegetle Consumption #2 per wk per wk per wk per dy per dy per dy $3 per dy Fruit Consumption,1 per wk per wk per wk per wk per dy $2 per dy Age-djusted reltive frequeny distriutions, see Tle II. Q, No Q, see Tle I. Signifint differene, see Tle II. distriutions did not differ signifintly y response sttus in either stte y the stringent rejetion riterion (lthough in, p for res plnted nd p for numer of livestok). There were no signifint differenes etween nonrespondents nd respondents in the numer of yers involved in pestiide mixing nd pplition fter ge djustment, ut there were differenes in the numer of dys spent in the pst yer in pestiide mixing nd pplition (p in ), with responders spending fewer dys mixing nd pplying pestiides thn nonresponders in oth sttes. Tle VI exmines the types of pestiides pplied personlly y frmers in the pst yer, oth y generl lss of pestiide, nd y individully speified pestiides. Heriide pplition ws the most ommon type of pestiide pplition in oth sttes, nd responders were more likely thn nonresponders to hve pplied heriides in oth sttes (p for ). responders were lso more likely to hve pplied numer of speifi heriides, while responders in oth sttes were more likely to hve pplied the heriide glyphoste. The results for ever hving pplied speifi pestiides (dt not shown) were similr to the results for pplition in the pst yer, with responders hving pplied numer of different heriides signifintly more often in, nd glyphoste signifintly more often in oth sttes. Responders were somewht more likely to Q No Q Q NoQ Numer of Ares Plnted in Pst 12 Months None , $1, Numer of Livestok Tended in Pst 12 Months None , $1, Pestiide Mixing nd Applition: Durtion #1 yr yr yr yr yr yr Pestiide Mixing nd Applition: Frequeny,5 dys/yr dys/yr dys/yr dys/yr dys/yr $60 dys/yr Age-djusted reltive frequeny distriutions, see Tle II. Q, No Q, see Tle I. Signifint differene, see Tle II. hve ever pplied insetiides whih hd een on the mrket for longer period of time, suh s lindne, mlthion, nd rryl, s well s insetiides whih were no longer on the mrket, suh s hlordne nd hepthlor. Smll differenes in ever hving pplied 2,4,5-T nd DDT were not signifint. Methods used to pply pestiides re ompred in Tle VII. Although responders nd nonresponders were generlly

8 238 Trone et l. TABLE VI. Distriution (Perentge) of Pestiides Applied in the Pst Yer y Frmers Enrolled in the Agriulturl Helth Study TABLE VII. Distriution (Perentge) of Methods Used to Apply Pestiides for Frmers Enrolled in the Agriulturl Helth Study Q No Q Q NoQ Q No Q Q NoQ Generl Clss of Pestiide Heriide Insetiide d Insetiide e Fungiide Fumignt Heriides Alhlor Atrzine ,4-D Dim Glyphoste Imzethpyr Metolhlor Triflurlin Insetiides, Fungiides, nd Fumignts Permethrin d Terufos Fonofos Chlorpyrifos Coumphos Permethrin e Cptn Brom-O-Gs Chlorothlonil Age-djusted reltive frequeny distriutions, see Tle II. Q, No Q, see Tle I. Signifint differene, see Tle II. d Applied to rops. e Applied to nimls or poultry. similr in pestiide pplition methods, responders in oth sttes were signifintly more likely to use hnd spryers or kpk spryers. The greter use of hnd sprying devies y responders persisted fter strtified nlyses djusting for the numers of res plnted or the numer of dys per yer spent mixing nd pplying pestiides. Responders in were more likely to use oom spryers pulled y trtor, ut there ws no evidene of suh differene in North Crolin. As shown in Tle VIII, responders were slightly more likely to report use of protetive equipment while mixing nd pplying pestiides, lthough the differene ws signifint only for hemil resistnt glove use in. There were no signifint differenes in reported symptoms fter pestiide mixing nd pplition in either stte. Boom trtor Hnd spry Bkpk Gs nister Row fumigte Furrow/nded Seed treted Powder duster Mist lower Injet niml Dip niml Spry niml Er tgs Dust niml Age-djusted reltive frequeny distriutions, see Tle II. Q, No Q, see Tle I. Signifint differene, see Tle II. Tle IX summrizes the prtiiption of frmers in vriety of work tsks. Responders were somewht more likely to hve repired pestiide pplition equipment (p in ) nd to hve een involved in pinting (p in ). Nonresponders were slightly more likely thn responders to hve uthered nimls. In generl, however, responders nd nonresponders differed little in the types of tsks performed. Tle X ompres the distriutions of previous disese nd history of disese in t lest one first degree reltive. Responders did not report signifintly more prior dignoses of disese thn nonresponders, lthough there ws slight inrese in the perentge of responders reporting prior dignosis of ner. A higher perentge of responders reported dignosis of ny ner in first degree reltive in oth sttes (p for ); however, differenes in reported fmily history of speifi mlignnies were negligile. There ws no evidene in either stte of ny inrese y responders in the reporting of lymphopoieti mlignnies in themselves or their reltives. DISCUSSION The enrollment rte of 77% for the Agriulturl Helth Study ompres fvorly with enrollment rtes in previous lrge, prospetive studies in whih enrollment ws omplished through self-dministered questionnire. The British Dotors Study [Doll nd Hill, 1964] enrolled 69% of the men nd 60% of the women initilly pprohed, the

9 Response in the Agriulturl Helth Study 239 TABLE VIII. Distriition of Use of Pestiide Protetive Equipment nd Reported Symptoms After Pestiide Mixing nd Applition for Frmers Enrolled in the Agriulturl Helth Study Q No Q Q NoQ Pestiide Protetive Equipment Used Work gloves Chem gloves d Fe shield Gs msk Disp e lothes Symptoms After Pestiide Mixing nd Applition Tired Hedhes Nuse Skin Irr f Eye Irr f Chest pin Nervous See dotor Hospitlized Age-djusted reltive frequeny distriutions, see Tle II. Q, No Q, see Tle I. Chemil resistnt. d Signifint differene, see Tle II. e Disposle. f Irrittion. Nurses Helth Study [Brton et l., 1980] hieved 71% response rte, the Luthern Brotherhood Study [Chow et l., 1992] enrolled 68% of trgeted men, nd the Rdiologi Tehnologist Study [Boie et l., 1995] hd n enrollment rte sed only on the self-dministered questionnire of 68%. The Women s Helth Study [Potter et l., 1992] enrolled only 43% of women, ged yers, rndomly seleted from liensed drivers in. Erly investigtions regrding survey questionnire response indited tht higher response rtes ould e hieved in homogeneous popultion with shred interest in the reserh topi [Suhmn, 1940; Edgerton et l., 1943; Wlle, 1947]. The lower response rte in the Women s Helth Study my prtilly e explined y the more heterogeneous study popultion without n ovious shred helth onern. The higher enrollment rte for the Agriulturl Helth Study is noteworthy, euse it ws hieved using the longest enrollment questionnire of the ove-mentioned studies. This my reflet the homogeneous study popultion with shred interest in ftors ffeting the helth of frm fmilies. The high enrollment rte, however, is likely due in lrge prt to the ft tht the self-dministered enrollment TABLE IX. Distriution of Frm Tsks Performed y Enrolled Frmers in the Agriulturl Helth Study Q No Q Q NoQ Engine repir Pest repir d Buther niml d Vet e servies Brke lining Hndle grin Hndle hy Grind feed Hndle silge Weld Pint d Tend swine Age-djusted reltive frequeny distriutions, see Tle II. Q, No Q, see Tle I. Prestiide pplition equipment. d Signifint differene, see Tle II. e Veterinry. questionnire is filled out t pestiide sfety trining session rther thn t home. No informtion is ville regrding the 23% of eligile frmers who delined to fill out the enrollment questionnire, ut the experiene in the Agriulturl Helth Study with regrd to return rtes for the tke-home questionnire n, nonetheless, provide useful informtion for urrent nd future prospetive studies. In prtiulr, the omprison of return rtes for sujets who did, or did not, omplete the lengthy tke-home questionnire provides mens of ssessing the extent to whih prtiipnts in studies sed on self-dministered questionnires my represent ised smple with regrd to exposure or disese history. This is less of onern for outomes sertined through follow-up susequent to the ompletion of the questionnire (e.g., deths or ners identified in future yers y reord linkge) thn for outomes sertined vi the questionnire (e.g., some neurologi symptoms nd reprodutive outomes surveyed in the Agriulturl Helth Study). Overll, the responses on the enrollment questionnire of frmers who ompleted nd returned the tke-home questionnire were remrkly similr to the responses on the enrollment questionnire of frmers who did not return the tke-home questionnire. Even when there were signifint differenes etween responders nd nonresponders, the mgnitude of the differenes were, in generl, not sustntil, usully differing y only few perent. In prtiulr, differenes with regrd to importnt, known risk ftors for ner, suh s ever smoking igrettes, use of snuff or

10 240 Trone et l. TABLE X. Distriution of Disese Dignoses nd Fmily History of Disese for Frmers Enrolled in the Agriulturl Helth Study Q No Q Q NoQ Previously Dignosed in Frmers Asthm Pneumoni Melnom Skin ner Hodgkin s Disese Non-Hodgkin s lymphom Leukemi Any ner d Hert disese Dietes Kidney disese Depression Disese Dignosed in First-Degree Reltive Brest ner Lung ner Colon ner Melnom Skin ner Stomh ner Lymphom Leukemi Brin ner Prostte ner Any ner d e Hert ttk Dietes Kidney filure Age-djusted reltive frequeny distriutions, see Tle II. Q, No Q, see Tle I. Nonmelnom skin ner. d Exluding skin ner. e Signifint differene, see Tle II. hewing too, lohol onsumption, nd fmily history of speifi mlignnies, were smll, s were differenes in known protetive ftors, suh s vegetle nd fruit onsumption. The most notle differene etween nonresponders nd responders ws the inresed ge of responders. This does not pose fundmentl prolem for future nlyses of ssoitions etween exposures nd disese risk, however, euse ll suh nlyses will e ge-djusted. Previous findings relted to ge nd nonresponse hve een mixed, with some studies reporting no reltionship [Okes et l., 1973; Criqui et l., 1978] or diret reltionship [Sheikh nd Mttingly, 1981; Clrk et l., 1983; Wlker et l., 1987; Bkke et l., 1990; Pnser et l., 1994] etween ge nd response rte, ut other studies reporting n inverse reltionship [Doll nd Hill, 1964; Brton et l., 1980; Benfnte et l., 1989; Mer et l., 1990; Heilrun et l., 1991; Melton et l., 1993; Bisgrd et l., 1994] etween ge nd response rte. The diretion of the ssoition etween ge nd response rte will likely depend on hrteristis of the study popultion, the purpose of the study, nd study reruitment methods. Exmintion of vrious preditors of response in the Agriulturl Helth Study suggests tht the mount of ville free time my e mjor determinnt of whether the self-dministered, tke-home questionnire ws ompleted, nd tht this ould explin the diret reltionship etween ge nd response rte. There ws n inverse reltionship etween ge nd the extent of frming enterprises, inditing tht younger frmers were likely spending more time involved in frming opertions, leving less time for filling out the tke-home questionnire. In support of this onlusion, nonresponders reported plnting more res, tending lrger numer of livestok, nd spending more dys per yer involved in personlly mixing nd pplying pestiides thn responders. These results suggest tht the study popultion my hve lower urrent exposure, ut higher umultive exposure, thn the study se popultion of ll frmer pplitors. Nonresponders lso tended to hve lrger fmilies nd slightly greter likelihood of hving young hild t home, inditing tht fmily responsiilities might hve redued the time ville for filling out questionnire. Finlly, the response rte in oth sttes ws signifintly higher during winter months, when less time is required for frming tivities. The most onsistent findings of previous studies of response hve een tht responders re etter eduted [Brton et l., 1980; Clrk et l., 1983; Benfnte et l., 1989; Heilrun et l., 1991; Melton et l., 1993] nd less likely to e urrent igrette smokers [Doll nd Hill, 1964; Okes et l., 1973; Seltzer et l., 1975; Criqui et l., 1978; Bkke et l., 1990; Benfnte et l., 1989; Mer et l., 1990; Heilrun et l., 1991; Bisgrd et l., 1994]. Both results re onfirmed y the results of the Agriulturl Helth Study, nd dditionl results, not diretly ville from prior investigtions of nonresponse, suggest tht responders re generlly more wre of, or more onerned out, helthrelted issues thn re nonresponders. Thus, responders onsumed lohol signifintly less often thn nonresponders, nd onsumed signifintly more fruits nd vegetles thn nonresponders. A higher prevlene of linil lohol prolems in nonresponders hs een reported previously [Wilhelmsen et l., 1976]. Responders were lso somewht more likely to report use of protetive equipment when mixing or pplying pestiides. Use of too prod-

11 Response in the Agriulturl Helth Study 241 uts other thn igrettes hs not een exmined in prior studies of nonresponse, lthough slightly slower response (i.e., the perentge of eventul responders who hd responded t n interim time point ws used s surrogte for response rte) in pipe nd igr smokers ws previously reported [Seltzer et l., 1975]. No ssoition ws oserved mong frmers etween response sttus nd igr or pipe smoking or the use of hewing too or snuff. Responders nd nonresponders differed slightly in univrite nlyses with regrd to igrette smoking nd lohol onsumption, whih re risk ftors for severl types of ner, nd vegetle onsumption, whih is protetive ftor for numer of types of ner. Thus, there might e onern tht omintion of suh vriles might led to lrger differene etween responders nd nonresponders in n umultion of ftors ssoited with inresed risk of ner. Aordingly, omprisons were mde of the perentge of sujets who were urrent smokers, drnk lohol t lest one time week, nd te vegetles less thn 5 times week. The ge-djusted perentges for this omintion of ftors were 5.2% in responders, 7.8% in nonresponders, 4.9% in responders, nd 7.6% in nonresponders. Although signifint in oth (p ) nd (p ), the mgnitude of the differenes, s in the se of univrite omprisons, ws not sustntil. Previous dignoses of disese or physil prolems ssoited with pestiide pplition did not pper to hve motivted frmers to fill out nd return the tke-home questionnire. Likewise, differenes in reported fmily history of vriety of speifi ners nd other diseses were ll negligile. Responders in were more likely to hve mixed nd pplied heriides, nd reported somewht greter use of protetive equipment when mixing nd pplying pestiides. The interprettion of the greter use of hnd sprying devies nd more frequent repir of pestiide pplition equipment y responders is unertin, ut my indite pereption of greter personl pestiide exposure. Tken together, these differenes might indite n inresed motivtion to prtiipte due to onern resulting from puliity generted y previous epidemiologi studies tht suggested possile disese risks ssoited with heriide exposure. A numer of these previous studies, some of whih were onduted in, reported tht heriide exposure ws possily ssoited with n inresed risk of lymphopoieti mlignnies [Hor et l., 1986; Brown et l., 1990; Zhm et l., 1990; Cntor et l., 1992]. Therefore, if pst epidemiologi studies were influening prtiiption in the Agriulturl Helth Study, evidene might e expeted to ome from self-reports of the onditions most strongly ssoited with frming in these studies, nmely, lymphti nd hemtopoieti ners. In ft, no greter dignosis of, or fmily history of, lymphopoieti ners ws reported y responders. For questions on the enrollment questionnire whih required study sujets to provide informtion on numer of relted items (e.g., whih of severl listed pestiides they hd pplied) responders tended to report slightly higher perentges thn nonresponders for most items (Tles VI X). Rther thn representing fundmentl exposure differenes etween responders nd nonresponders whih ould ffet the ssessment of disese risk, these systemti differenes on multiple item questions my simply indite tendeny for responders to e more ompulsive in performing tsks. Suh n inferene is quite speultive, ut like the more reful nd omplete reporting on the multiple item questions from the enrollment questionnire, the higher response rte for the tke-home questionnire ould reflet greter sense of responsiility nd oligtion when fed with ny tsk. Suh personlity trit my lso explin why responders were signifintly more likely to report personl pplition of glyphoste, n heriide often used for totl weed ontrol in res not diretly involved in rop prodution, nd why signifintly higher perentge of responders reported tht they pinted on their frms. Both differenes my reflet more ompulsive onern of responders regrding the pperne of their property. Although the oserved differenes etween responders nd nonresponders re, in generl, reltively smll in mgnitude, dditionl investigtions hve een initited within the Agriulturl Helth Study ohort to exmine the potentil for responder is nd to determine the extent to whih findings n e generlized to wider popultion, prtiulrly for outomes sertined through the tke-home questionnire. Aordingly, three rndom smples, one of 1,000 enrolled mle sujets nd two seprte smples of 1,000 femle spouses of enrolled frmers, will e studied in greter detil. The mle smple will e omposed of men yers of ge. One femle smple will e omposed of women yers of ge nd the seond of women yers of ge. Nonrespondents in eh smple will e ontted for telephone interview overing seleted questions from the longer, tke-home questionnires. These su-studies will evlute the potentil for is in the ssessment of reprodutive history (e.g., spontneous ortion rtes or ge t menopuse) in women nd of neurologi nd immunologi diseses in men. The enrollment questionnire in the Agriulturl Helth Study ws 17 pges long, nd thus it ws possile to evlute the impt on response of mny more vriles thn were exmined in previous studies of response. In spite of the length of the enrollment questionnire, the enrollment rte ws higher thn hs een oserved in other lrge prospetive studies, nd thus our investigtion involved lrger perentge of the trgeted popultion thn most previous studies of response. Our study of frmers enrolled in the Agriulturl Helth Study found little differene etween the hrteristis of sujets who ompleted only the enrollment question-

12 242 Trone et l. nire nd those who lso hose to omplete nd return the lengthy, tke-home questionnire. Although sttistilly signifint differenes etween respondents nd nonrespondents were oserved, most were smll in mgnitude nd would not e expeted to ompromise etiologi inferenes sed on prospetively sertined helth outomes. Age, the ttriute tht vried most etween responders nd nonresponders, is esily tken into ount in sttistil nlyses. The lk of evidene for sustntil seletion is is ressuring for the Agriulturl Helth Study nd, lthough the potentil for seletion is should e evluted in eh study, my provide some ressurne for other epidemiologi studies whih depend upon voluntry ompletion of self-dministered questionnires. REFERENCES Alvnj MCR, Sndler DP, MMster SB, Zhm SH, MDonnell CJ, Lynh CF, Pennyker M, Rothmn N, Dosemei M, Bond AE, Blir A (1996): The Agriulturl Helth Study. Environ Helth Perspet 104: Bkke P, Gulsvik A, Lilleng P, Over O, Hno R, Eide GE (1990): Postl survey on irorne ouptionl exposure nd respirtory disorders in Norwy: uses nd onsequenes of non-response. J Epidemiol Community Helth 44: Brton J, Bin C, Hennekens CH, Rosner B, Belnger C, Roth A, Speizer FE (1980): Chrteristis of respondents nd non-respondents to miled questionnire. Am J Puli Helth 70: Benfnte R, Reed D, MLen C, Kgn A (1989): Response is in the Honolulu hert progrm. Am J Epidemiol 130: Bisgrd KM, Folsom AR, Hong CP, Sellers TA (1994): Mortlity nd ner rtes in nonrespondents to prospetive study of older women: 5-yer follow-up. Am J Epidemiol 139: Blir A (1992): An overview of potentil helth hzrds mong frmers from use of pestiides. In Myers ML, Herrik RF, Olenhok SA, Myers JR, Prker JE, Hrd DL, Wilson K (eds): Ppers nd Proeedings of the Surgeon Generl s Conferene on Agriulturl Sfety nd Helth. DHHS (NIOSH) Pul # Cininnti, OH, pp Blir A, Zhm SH (1991): Cner mong frmers. In Cordes DH, Re DF (eds): Helth Hzrds of Frming. Oup Med: Stte of the Art Reviews 6: Phildelphi: Hnley nd Belfus. Boie JD, Mndel JS, Doody MM (1995): Brest ner mong rdiologi tehnologists. JAMA 274: Brown LM, Blir A, Gison R, Everett G, Cntor KP, Shumn L, Burmeister L, Vn Lier S (1990): Pestiide exposures nd other griulturl risk ftors for leukemi mong men in nd Minnesot. Cner Res 50: Cntor KP, Blir A, Everett G, Gison R, Burmeister LF, Brown LM, Shumn L, Dik FR (1992): Pestiides nd other griulturl risk ftors for non-hodgkin s lymphom mong men in nd Minnesot. Cner Res 52: Chow WH, Shumn LM, MLughlin JK, Bjelke E, Gridley G, Wholder S, Co Chien HT, Blot WJ (1992): A ohort study of too use, diet, ouption, nd lung ner mortlity. Cner Cuses Control 3: Clrk VA, Aneshensel CS, Frerihs RR, Morgn TM (1982): Anlysis of non-response in prospetive study of depression in Los Angeles County. Int J Epidemiol 12: Criqui MH, Brrett-Connor E, Austin M (1978): Differenes etween respondents nd non-respondents in popultion-sed rdiovsulr disese study. Am J Epidemiol 108: Doll R, Hill AB (1964): Mortlity in reltion to smoking: ten yers oservtions of British dotors. Br Med J 1: Edgerton HA, Britt SH, Norml RD (1943): Ojetive differenes mong vrious types of respondents to miled questionnire. Am Soiol Rev 8: Heilrun LK, Nomur A, Stemmermnn GN (1991): The effets of non-response in prospetive study of ner: 15-yer follow-up. Int J Epidemiol 20: Hor SK, Blir A, Holmes FF, Boysen CD, Roel RJ, Hoover R, Frumeni JF JR (1986): Agriulturl heriide use nd risk of lymphom nd soft-tissue srom. JAMA 256: Mer CA, Jkson KL, Dvis DR, Kronenfeld JJ, Blir SN (1990): Ptterns of non-response to mil survey. J Clin Epidemiol 43: Melton LJ, Dyk PJ, Krnes JL, O Brien PC, Servie FJ (1993): Nonresponse is in studies of dieti omplitions: The Rohester Dieti Neuropthy Study. J Clin Epidemiol 46: Miller RG (1981): Simultneous Sttistil Inferene. New York: Springer-Verlg. Okes TW, Friedmn GD, Seltzer CC (1973): Mil survey response y helth sttus of smokers, nonsmokers, nd ex-smokers. Am J Epidemiol 98: Pnser LA, Chute CG, Guess HA, Lrsonkeller JJ, Girmn CJ, Oesterling JE, Lieer MM, Josen SJ (1994): The nturl history of prosttism: The effets of non-response is. Int J Epidemiol 23: Potter JD, Sellers TA, Folsom AR, MGovern PG (1992): Alohol, eer, nd lung ner in postmenopusl women: The Women s Helth Study. Ann Epidemiol 2: Seltzer CC, Bosse R, Grvey AJ (1975): Mil survey response y smoking sttus. Am J Epidemiol 100: Sheikh K, Mttingly S (1981): Investigting non-response is in mil surveys. J Epidemiol Community Helth 35: Suhmn EA, MCndless B (1940): Who nswers questionnires? J Appl Psyhol 24: Thoms DG, Grt JJ (1983): Strtified trend nd homogeneity nlysis of proportions nd life tle dt. Comp Biomed Res 16: Wholder S, MLughlin JK, Silvermn DT, Mndel JS (1992): Seletion of ontrols in se-ontrol studies. I. Priniples. Am J Epidemiol 135: Wlle D (1947): Mil questionnires n produe good smples of homogeneous groups. J Mrketing 12: Wlker M, Shper AG, Cook DG (1987): Non-prtiiption nd mortlity in prospetive study of rdiovsulr disese. J Epidemiol Community Helth 41: Wilhelmsen L, Ljungerg S, Wedel H, Werko L (1976): A omprison etween prtiipnts nd non-prtiipnts in primry preventive tril. J Chron Dis 29: Zhm SH, Weisenerger DD, Bitt PA, Sl RC, Vught JB, Cntor KP, Blir A (1990): A se-ontrol study of non-hodgkin s lymphom nd the heriide 2,4-dihlorophenoxyeti id (2,4-D) in estern Nersk. Epidemiology 1: