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1 University of Groningen The prevlene of sesonl ffetive disorder in the Netherlnds Mersh, PPA; Middendorp, HM; Bouhuys, Antoinette; Beersm, DGM; vn den Hoofdkker, RH; Middendorp, Hermine M. Pulished in: Biologil Psyhitry DOI: /S (98) IMPORTANT NOTE: You re dvised to onsult the pulisher's version (pulisher's PDF) if you wish to ite from it. Plese hek the doument version elow. Doument Version Pulisher's PDF, lso known s Version of reord Pulition dte: 1999 Link to pulition in University of Groningen/UMCG reserh dtse Cittion for pulished version (APA): Mersh, P. P. A., Middendorp, H. M., Bouhuys, A. L., Beersm, D. G. M., vn den Hoofdkker, R. H., & Middendorp, H. M. (1999). The prevlene of sesonl ffetive disorder in the Netherlnds: A prospetive nd retrospetive study of sesonl mood vrition in the generl popultion. Biologil Psyhitry, 45(8), DOI: /S (98) Copyright Other thn for stritly personl use, it is not permitted to downlod or to forwrd/distriute the text or prt of it without the onsent of the uthor(s) nd/or opyright holder(s), unless the work is under n open ontent liense (like Cretive Commons). Tke-down poliy If you elieve tht this doument rehes opyright plese ontt us providing detils, nd we will remove ess to the work immeditely nd investigte your lim. Downloded from the University of Groningen/UMCG reserh dtse (Pure): For tehnil resons the numer of uthors shown on this over pge is limited to 10 mximum. Downlod dte:

2 The Prevlene of Sesonl Affetive Disorder in The Netherlnds: A Prospetive nd Retrospetive Study of Sesonl Mood Vrition in the Generl Popultion Peter Pul A. Mersh, Hermine M. Middendorp, Antoinette L. Bouhuys, Domien G.M. Beersm, nd Rutger H. vn den Hoofdkker Bkground: The im of the present study ws to ssess the prevlene of sesonl ffetive disorder (SAD) in The Netherlnds. Methods: The sujets (n 5356), rndomly seleted from ommunity registers, were given the Sesonl Pttern Assessment Questionnire nd the Centre for Epidemiologil Studies Depression Sle over period of 13 months. The response rte ws 52.6%. Results: Three perent of the respondents met the riteri for winter SAD, 0.1% for summer SAD. The riteri for susyndroml SAD, milder form of SAD, were met y 8.5%, 0.3% of whom showed summer pttern. Younger women reeived dignosis of SAD more often thn men or older women. Conlusions: SAD sujets were signifintly more often unemployed or on sik leve thn other sujets. Respondents who met winter SAD riteri were signifintly more depressed thn helthy sujets, in oth winter nd summer. Finlly, month of ompletion hd no influene on the numer of sujets meeting the SAD riteri. Biol Psyhitry 1999 Soiety of Biologil Psyhitry Key Words: Sesonl ffetive disorder, prevlene, epidemiology, mood vrition Introdution Dt on the prevlene of sesonl ffetive disorder (SAD) hve umulted over the pst 5 yers. The use of the sme instrument in nerly ll studies, the Sesonl Pttern Assessment Questionnire (SPAQ; Rosenthl et l 1987) nd the pplition of (more or less) the sme riteri [formulted y Ksper et l (1989)] filittes the omprison of studies (Rosen et l 1990). Results from studies on smples from the generl popultion in the USA (Ksper et l 1989; Rosen et l 1990; From the Deprtment of Biologil Psyhitry, University Hospitl Groningen, Groningen, The Netherlnds. Address reprint requests to Dr. P.P.A. Mersh, Deprtment of Biologil Psyhitry, University Hospitl Groningen, P.O. Box 30001, 9700 RB Groningen, The Netherlnds. Reeived June 23, 1997; revised Ferury 10, 1998; revised April 29, 1998; epted My 11, Termn 1988; Booker nd Hellekson 1992) show prevlene rtes of %. This lrge rnge n prtly e explined y ltitude differenes in smples studied (27 N 64 N) (Potkin et l 1986; Lingjerde et l 1986). Differenes in prevlene rtes in Europen studies re smller thn in the USA. In Switzerlnd (47 N; Wirz- Justie et l 1992), 2.2% of the popultion ws estimted to suffer from SAD, while in Ielnd (62 N 67 N; Mgnusson nd Stefnsson 1993), the SAD riteri of the SPAQ were met y 3.8% of the responders. One study ws performed t the sme time in Sweden nd Finlnd. In oth ountries the SPAQ ws sent to rndom smple of the popultion (Hgfors et l 1995). The prevlene rte in Sweden (55 N 69 N) ws 3.9%, wheres this figure ws lmost twie s high in Finlnd (60 N 70 N). This high SAD rte in Finlnd (7.1%) not only devites from the figures in Sweden nd Ielnd, ut lso from n erlier Finnish study (Hgfors et l 1992), whih reveled prevlene rte of 3.4%. In Itly (39 N 46 N; Musettol et l 1995). The prevlene rte for winter SAD ws 4.4% nd for summer SAD 2.1%. The reliility of these figures is, however, doutful, sine the response rte ws extremely low (13.6%). In most studies, more women thn men met SAD riteri, nd younger women more often thn older women. This study estimted the prevlene of SAD in The Netherlnds. In ddition, the role of demogrphi nd soil vriles in SAD is studied. A speil spet of the study is tht pproximtely 400 questionnires were sent eh month over period of 13 months. This wy, mood ws oth retrospetively s well s diretly ssessed t different points in time. The purpose of this design ws twofold: 1) to study the influene of month of ompletion of the questionnire on sesonlity nd on the prevlene rte of SAD; nd 2) to study the vrition of mood over the sesons. Methods nd Mterils Smple A totl numer of 5356 sujets ws seleted rndomly from the ommunity registers of 15 ommunities in the three northern 1999 Soiety of Biologil Psyhitry /99/$19.00 PII S (98)

3 1014 BIOL PSYCHIATRY P.P.A. Mersh et l provines of The Netherlnds. The ommunities nd the numers drwn from eh ommunity were hosen in suh wy tht the smple ws representtive for the urniztion level of The Netherlnds. The perentge of men nd women ws equl. The ge rnge ws hosen etween 18 nd 65 yers. Instruments The questionnire pkge sent out ontined three groups of vriles: DEMOGRAPHIC VARIABLES. In this setion informtion on ge, gender, mritl sttus, edution, work, sik leve, ody length, nd weight ws sked. SEASONAL VARIABLES. To ssess (different spets of) SAD, the SPAQ (Rosenthl et l 1987) ws inluded. The SPAQ riteri (self-report version) for SAD, formulted y Ksper et l (1989), onsist of three prts. The Glol Sesonlity (GS) sore is omposite mesure sking for hnge ross the sesons on six spets: mood, soil tivities, ppetite, sleep, weight, nd energy. Eh item hs Likert-type sles, rnging from (0) no hnge to (4) extremely mrked hnge. The totl sle rnges from 0 to 24, with suggested utoff sore of 11 for seness. The seond prt of the riteri for SAD is the question whether sesonl hnges re onsidered prolem. The response tegories re 0 no prolems, 1 mild, 2 moderte, 3 mrked, 4 severe prolems, nd 5 disling. A sore of t lest 2 is neessry to reh the SAD threshold. Finlly, the timing of the sesonl prolems (summer or winter) is determined y sking wht months sujets feel worst (the window ). This riterion differs from one study to the next. In the present study, window from Otoer through Mrh delinetes winter pttern nd window from April through Septemer summer pttern. Susyndroml SAD (S-SAD) is hrterized y indequte funtioning in ertin sesons, while the symptoms re not severe enough to llow for dignosis of SAD. The riteri of S-SAD re: 1) GS sore of t lest 11 nd no or mild prolems with the sesonl hnges; or 2) GS sore of 9 or 10 nd sesonl hnges re experiened s either prolem or not (Ksper et l 1989). The window for S-SAD is the sme s for SAD. In ddition to the items representing the riteri for SAD nd S-SAD, severl other relevnt vriles were inluded. Two items on the level of energy over the months were dded. Likert-type sles were used to sore hours of sleep in eh seson on sle rnging from 1 (3 hours or less) to 12 (14 hours or more); hours spent outside in eh seson on sle rnging from 1 (1 hour or less) to 10 (10 hours or more); nd weight hnge over the yer on sle rnging from 1 (less thn 2 kg) to 6 (more thn 10 kg). Finlly, the influene of limti onditions on mood ws ssessed y seven-point sles, rnging from 3 (very low spirits or mrkedly slowed down to 3 (mrkedly improved mood or energy level). Moreover, questions onerning the onsequenes of sesonl prolems, inluding onsumption of medition nd senteeism, were dded to the questionnire. DEPRESSIVE COMPLAINTS, INDEPENDENT OF SEASON. Severl questions on episodes of depressed mood independent of seson were inluded: on the numer of episodes during the lst 5 yers (rnging from 0 to 4 times or more), on the symptoms ssoited with these episodes, nd on the extent to whih sujets were othered y these symptoms (rnge: 0 not t ll othered to 4 very muh othered ). To mesure depression, the Centre for Epidemiologil Studies Depression Sle (CES-D; Ensel 1986) ws inluded. The CES-D mesures the frequeny of depressive feelings nd ehviors over the pst week. It onsists of 20 Likert-type sles, rnging from 0 (rrely to never) to 3 (mostly or ll the time). The rnge of the totl sle is A totl sle sore of 16 or higher is rough inditor of depression nd reflets possile seness (Ensel 1986). Proedure To ontrol for urniztion in The Netherlnds, the urniztion level ws divided in five lsses (from ommunities with fewer thn 10,000 inhitnts to ommunities with more thn 100,000 inhitnts). Fifteen ommunities were rndomly seleted in suh wy tht the smple ws representtive of the urniztion level in The Netherlnds. The questionnires were miled in 13 onseutive months to investigte the influene of the month in whih prevlene studies re performed on results nd to study mood vrition over the sesons. The first week of Mrh questionnires were sent out. To ontrol for nonresponse used y hnge of ddress, the numer of questionnires sent ws rised y two every first week of eh following month: in April questionnires were sent, in My , et. In the lst month, Mrh 1994, 424 questionnires were sent. This wy totl of 5356 questionnires ws rehed. To mke sure tht eh smple ws representtive with respet to urniztion level, eh month rndom smple ws drwn from the remining sujets of the reserh popultion of ll 15 ommunities. Results Responses The response rte per month vried from 49.0% to 56.8%. The totl response ws 2819 questionnires (52.6%). Signifintly more women thn men responded (54.0% versus 45.8%; 0.2% of the dt on gender were missing) ( , p.0001). Sesonl Affetive Disorder SAD riteri were met y 3.1% of the respondents (n 88), with 3% (n 85) showing winter pttern. Using 95% onfidene intervl (2 SD), % of the Duth popultion etween 18 nd 65 yers of ge suffers from

4 SAD in The Netherlnds BIOL PSYCHIATRY 1015 Tle 1. Demogrphi Vriles of the Three Groups SADW (n 85) (3.0%) S-SADW (n 230) (8.2%) NSAD (n 2054) (88.8%) Anlyses p Gender Femle 67 (78.8%) 155 (67.4%) 1299 (51.9%) 2 (2) Mle 18 (21.2%) 74 (32.2%) 1200 (47.9%) Men ge (SD) 36.5 (11.45%) 35.6 (12.43) 39.7 (13.18) F (2,2784) Level of edution Low 24 (28.2%) 51 (22.2%) 709 (28.3%) 2 (6) 6.08 ns Medium 30 (35.3%) 84 (36.5%) 883 (35.3%) High 22 (25.9%) 67 (29.1%) 609 (24.3%) Very high 6 (7.1%) 25 (10.9%) 273 (10.9%) Civil sttus Mrried 45 (52.9%) 125 (54.3%) 1520 (60.7%) 2 (2) 3.13 ns Living together 14 (16.5%) 26 (11.3%) 263 (10.5%) Living lone 19 (22.4%) 65 (28.3%) 566 (22.6%) Divored 4 (4.7%) 8 (3.5%) 81 (3.2%) Widow/widower 3 (3.5%) 5 (2.2%) 67 (2.7%) This lultion ws performed etween the omined tegories 1 nd 2 nd the omined tegories 3, 4, nd 5. winter SAD. Criteri for S-SAD were met y 239 respondents (8.5%), of whom nerly ll (n 230) met riteri for winter S-SAD (95% onfidene intervl: %). Chrteristis of SAD To study the symptomti, demogrphi, nd soil hrteristis of SAD sujets, respondents were divided into three groups: winter SAD (SADW), winter S-SAD (S- SADW), nd group tht did not meet the SAD/S-SAD riteri (NSAD). Nerly four times s mny women reeived dignosis of winter SAD s men (3.7:1); for S-SADW the proportion ws 2.1:1 (Tle 1). The differene etween the three groups ws highly signifint. Both SADW nd S-SADW groups were younger thn the NSAD group, ut no etween-group differenes in edution level or ivil sttus were found. Civil sttus onerned those sujets who were mrried or were living together with prtner nd those who lived lone, sine smll numers of divored/widowed sujets preluded nlysis. WORK AND ABSENTEEISM. More people in the SADW group were unemployed thn in the S-SADW or NSAD group (Tle 2). The sme pplies to periods of sik leve. Of the employed SADW sujets 42.2% sried short periods of senteeism to their sesonl prolems, ompred to 14.2% of the S-SADW nd 4.1% of the NSAD groups. These differenes were highly signifint. The men period of senteeism ws numerilly longer in the SADW groups, ut this differene ws not signifint. Nerly two thirds (65.9%) of the SADW group sought tretment for their sesonl prolems (Tle 3), whih ws higher thn the S-SADW nd NSAD groups ( 2 (2) 14.51, p.001). Notly, 63.2% of sujets who hd sought tretment for their sesonl prolems reeived medition, in most ses presried y their generl prtitioner. Of SADW sujets 41.1% hd onsulted psyhologist, while 8.9% onsulted medil speilist. Tle 4 summrizes the results on different spets of SAD in the SADW, S-SADW, nd NSAD groups for men Tle 2. Employment nd Asenteeism SADW S-SADW NSAD Anlyses p Unemployed 38 (44.7%) 74 (32.3%) 854 (34.1%) On sik leve 12 (14.1%) 19 (8.3%) 212 (8.5%) 2 (4) Employed 35 (41.2%) 136 (59.4%) 1437 (57.4%) If employed, sene euse of sesonl prolems No sene 19 (57.6%) 115 (85.8%) 1374 (95.9%) Asene 14 (42.4%) 19 (14.2%) 58 (4.1%) 2 (2) Men numer of dys F (2) ns

5 1016 BIOL PSYCHIATRY P.P.A. Mersh et l Tle 3. Help Reeived for Sesonl Prolems Sesonl prolems [n (% of smple)] Help reeived [n (% of sesonl prolems)] Kind of help reeived Medition Generl prtitioner Speilist Psyhologist Other SADW 85 (100%) 56 (65.9%) 34 (60.7%) 34 (60.7%) 5 (8.9%) 23 (41.1%) 11 (19.6%) S-SADW 103 (44.8%) 42 (40.8%) 20 (45.5%) 31 (70.5%) 9 (20.5%) 10 (22.7%) 9 (20.5%) NSAD 358 (14.3%) 160 (44.7%) 109 (66.1%) 112 (67.9%) 32 (19.4%) 36 (21.8%) 21 (12.7%) All sujets who reported hving sesonl prolems were sked whether they reeived help for these prolems. nd women seprtely. Differenes etween groups on GS sore nd perentge of sesonl prolems were highly signifint, whih is not surprising sine oth these vriles were seletion riteri. Women in the SADW nd the S-SADW group slept signifintly more in the utumn nd winter ompred to the NSAD group. They lso slept longer in winter thn in summer. Moreover, women showed more weight hnge over the yer. For men these results re only true for the S-SADW group. Exlusively in women, the tul weight t the moment of ompletion of the questionnires ws higher in the SADW group thn in the other groups. As expeted, this result is minly due to the dt of the women who ompleted the questionnires in winter. Both men nd women in the SADW group spent more time outside in summer ompred to those in the NSAD group. This differene ws lso found in the S-SADW group, ut only for women. Moreover, women lso spent more time outside in summer thn in winter. There were no signifint differenes etween groups on ny of these vriles for men. The results on limti onditions re presented in Tle 5. On the right the men nd stndrd devition of the three groups re presented, s well s the results of n nlysis of vrine nd post ho test. The sle rnges from 3 (negtive influene) to 3 (positive influene). There were signifint differenes (t lest p.01) etween the groups on ll vriles ut high pollen ount. In most ses the sores of the two SAD groups were more extreme thn those of the NSAD group. This is lso demonstrted y the perentge of sujets who stted tht Tle 4. Symptoms nd Chrteristis of the Different Groups for Men nd Women Women SADW S-SADW NSAD Men SD Men SD Men SD p SNK Men SD Men SD Men SD p SNK Glol sesonlity Sesonl prolems [n (%)] 67 (100%) 64 (41.8%) 198 (15.5%), 18 (100%) 40 (54.1%) 164 (13.8%), Men severity , ,3 Hours of sleep Winter d 2 3 Spring ns ns Summer ns ns Autumn Winter summer Weight hnge (kg) Weight (kg/m) , ns Winter d 1 2,3 e Summer ns e Hours spent outside Winter ns ns Sping ns ns Summer d ns Autumn ns ns Summer winter ns Men SADW S-SADW NSAD SNK, Student Newmn-Keuls post ho omprisons t the lph.05 level; 1, 2, nd 3 refer to the groups SADW, S-SADW, nd NSAD, respetively. All nlyses re ANOVAs unless otherwise indited. Overll signifine p Differenes in frequeny re lulted y hi-squre. Overll signifine p.05. d Overll signifine p.01. e The numer of SADW nd S-SADW sujets is too smll to llow omprisons.

6 SAD in The Netherlnds BIOL PSYCHIATRY 1017 Tle 5. Wether Conditions nd Mood in the Three Groups Sle mens Perentge no effet on mood SAD S-SAD NSAD SADW (%) S-SAD (%) NSAD (%) p Men SD Men SD Men SD F p SNK Cold wether Hot wether d Humid wether Sunny dys Dry dys e 2 3 Gry, loudy dys Long dys d 2 1,3 High pollen ount f Foggy, smoggy dys Short dys SNK, Student Newmn Keuls post ho omprisons t the lph.05 level; 1, 2, nd 3 refer to the groups SADW, S-SADW, nd NSAD, respetively. Sle rnge: 3 to 3. Signifint hi-squre (df 2) t p Signifint F t p d Signifint F t p.001. e Signifint F t p.01. f Signifint hi-squre (df 2) t p.01. the wether does not ffet their mood. In oth SAD groups this perentge ws signifintly lower when ompred to the perentge of the NSAD group. The onlusion is tht the mood of sujets who met the riteri of winter SAD or winter S-SAD depends more on the wether thn tht of sujets who did not meet these riteri. This dependene would seem to onern the wether in generl, not speifi types of wether. Comprison of the three groups showed reltionship etween SAD nd depression t the moment the questionnires were ompleted (Tle 6). The SADW group sored signifintly higher thn the two other groups on the CES-D, nd the S-SADW group sored signifintly higher thn the NSAD group. By definition, winter SAD nd winter S-SAD ptients re expeted to e depressed in winter nd not in summer. To investigte this, the CES-D sores of the sujets who ompleted the questionnires in winter were ompred with the sores of the sujets who did so in summer. To rete groups tht re s extreme s possile winter nd summer were restrited to 3 months eh (Deemer, Jnury, nd Ferury versus June, July, nd August). As expeted, in the winter months oth SADW groups sored signifintly higher on the CES-D thn the NSAD group. Unexpetedly, however, the three groups lso differed signifintly in the summer months. As shown efore, there were nnul differenes in level of depression in the totl popultion. Therefore, smll derese in CES-D sore for the NSAD group in the summer months ws to e expeted. The redution ws signifint t the lph.001 level. The signifintly deresed summer level of depression in the S-SADW group ws something to e expeted s well. A surprising finding, however, ws tht the derese of men CES-D sore for the summer Tle 6. Depression SADW S-SADW NSAD Men SD Men SD Men SD Between group nlysis p SNK Depression t ompletion (CES-D) F (2,2765) CES-D winter (De, Jn, Fer) F (2,636) CES-D summer (June, July, Aug) F (2,627) ,3 Between-group ANOVA F (1,38) 0.42 F (1,89) F (1,1136) (summer versus winter) ns p.005 p.001 Reurrent depressive mood [n (%)] 85 (100%) 192 (83.5%) 1187 (47.4%) 2 (2) Frequeny F (2,1461) 9.53 Men numer of symptoms F (2,1460) Symptoms re prolem F (2,1451) ,3 SNK, Student Newmn Keuls post ho omprisons t the lph.05 level; 1, 2, nd 3 refer to the groups SADW, S-SADW, nd NSAD, respetively. p.001. Reurrent depressive mood depressive episodes independent of seson. p.0001.

7 1018 BIOL PSYCHIATRY P.P.A. Mersh et l months s ompred to the winter months for the SADW sujets ws smll nd not signifint. The sores in summer were still more thn two times s high in the SADW group thn in the other two groups. There ws signifint differene etween the groups in numers of sujets reporting t lest one episode of depressed mood over the lst 5 yers, independent of sesonl prolems. All sujets who met winter SAD riteri reported suh episodes. In the S-SADW nd NSAD groups, these perentges re 83.5% nd 47.4%, respetively. Also, the SADW group reported signifintly higher men frequeny of these episodes (more thn three over the pst 5 yers), more symptoms, nd more prolems euse of these symptoms thn the other groups. Mood Vrition over the Yer Mrh 1994 ws ontrol month for Mrh Sine no signifint differenes etween these two months were found on ny of the vriles, Mrh dt were pooled. There were onsiderle differenes etween months in the men sore on the CES-D [F (11,2756) 3.51, p.0001]. The lowest sore ws rehed in July (men 8.5, SD 8.33), the highest in Deemer (men 12.4, SD 10.34; see Figure 3). The differene etween the winter nd the summer months ws signifint [F (1,2766) 3.99, p.046]. The signifine ws inresed if the winter months were limited to Deemer, Jnury, nd Ferury, nd the summer months to June, July, nd August [F (1,1267) 18.76, p.0001]. Influene of Month of Completion on the SAD Criteri On the GS sore there ws signifint differene in the months of the yer [nlysis of vrine (ANOVA): F (11,2782) 2.104, p.017]. A post ho test (Student Newmn Keuls; SNK) showed tht the men sores in Ferury nd April were signifintly higher thn in Novemer (lph.05, Figure 1). To test whether there ws reltionship with mood, the GS sores were orrelted with the CES-D sores. Although signifint (Person r.36, p.001; two tiled), the orreltion ounted for only 13% of the vrine. To test whether mood t the moment of ompletion of the questionnire influened the GS sore, the ANOVA over the months ws repeted with the CES-D s ovrite. Apprently, mood flutution does not explin the differenes on the GS sore over the months; on the ontrry, inlusion of the CES-D in the model inreses the signifine level of the differene [F (11,2731) 2.544, p.003]. Figure 1. The influene of month of ompletion of the questionnire on the men GS sore (doule plot). The horizontl line shows the overll men. Comprison etween winter window (Otoer Mrh) nd summer window (April Septemer) reveled no signifint differenes etween GS sores. Figure 1 suggests tht the GS sores were higher when the SPAQ ws ompleted etween Deemer nd My thn etween June nd Novemer. Comprison showed tht this ws in ft the se [F (1,2792) 7.96, p.005]. The month of ompletion did not ffet whether or not sesonl hnges were experiened s prolem [ 2 (11) 7.911, p.721]. Also, the tul numer of sujets meeting the SAD riteri eh month did not differ from the expeted numer of sujets [ 2 (11) 12.54, p.325]. The sme result ws found if the sesons were ompred. Thus, lthough GS sore ws influened y month of ompletion, the omined SAD riteri of the self-report version of the SPAQ were hrdly sensitive to the month or seson in whih the SPAQ ws ompleted. Sesonlity The men GS sore for the totl popultion ws 4.79 (SD 3.51, medin 4.00), with 6.3% of the popultion sored 11. Women (men 5.26, SD 3.68) were signifintly [F (1,2786) 60.19, p.0001] more sensitive to sesonl hnges thn men (men 4.24, SD 3.21). For women, nd to lesser extent for men, sensitivity to sesonl hnges deresed with ge [F (4,1486) 17.99, p.0001 nd F (4,1264) 4.28, p.002, respetively] (Figure 2A). The Window More thn hlf of respondents (53.3%) hd one or more months of the yer in whih they felt worst. As expeted,

8 SAD in The Netherlnds BIOL PSYCHIATRY 1019 Figure 3. Retrospetive mood nd tul mood, ssessed t the moment of ompletion of the questionnire (doule plot). Figure 2. The reltionship etween GS sore nd ge (A) nd etween sesonl prolems nd ge (B), for mle nd femle sujets seprtely. the winter months (Otoer Mrh) were mentioned signifintly [ 2 (1) , p.0001] more often (79.3%) thn the summer months (April Septemer) (20.7%). Figure 3 shows the perentges of sujets who retrospetively indited tht they felt worst t the respetive time of the yer. In ddition, the monthly CES-D sores over the yer re depited, stte mesure of mood. The synhroniity etween the two urves n e onsidered s support of the onvergent vlidity. Prolems with Sesonl Chnges Prolems with the sesons were reported y 551 respondents (19.6%). More women (59.7%) thn men experiened these prolems [ 2 (1) 9.21, p.003] (Figure 2B). No differenes etween men nd women in the severity of sesonl prolems were found, nd experiening prolems with sesons did not depend on ge. In Figure 4, the seprte spets of sesonlity over the yer re distinguished. The dt were lulted ording to methods used in other studies (Wirz-Justie et l 1992; Thompson et l 1988). Eh point represents the perentge of the mximum otinle sore (4) on speifi sesonlity item, multiplied y the differene etween the months in whih people felt worse nd those in whih they felt est; the months in whih they slept most nd slept lest, et. Results re presented seprtely for respondents with nd those without sesonl prolems. At visul inspetion there is onsiderle differene etween sujets with nd those without sesonl prolems with respet to the ontriution of eh spet to the totl sesonlity sore, ut not with respet to the reltive ontriution of eh spet. To test whether this visul impression is vlid, the solute distnes from eh point to the x-xis were summed to otin mesure of the re under eh urve. The order of the mgnitude of the res under the urve is the sme in oth groups. Mood shows the lrgest vriility over the yer nd weight nd ppetite the smllest. Anlysis of vrine showed tht on ll six items the differenes etween the groups re signifint t the p.0001 level. Disussion In numer of respets the prevlene rte of SAD (3.1%) in the present study is in line with the expettions. In the first ple, this figure strengthens the positive reltionship etween prevlene nd ltitude. In the USA this orrel-

9 1020 BIOL PSYCHIATRY P.P.A. Mersh et l Figure 4. Perentge of the mximum otinle sore of eh GS item for the months sujets feel worst nd est over the yer (doule plot). (A) Sujets with sesonl prolems. (B) Sujets without sesonl prolems. tion (Spermn r s, one tiled) is r.90, p.003 (Mersh et l in press). When we exlude the unrelile Itlin dt (Musettol et l 1995), the prevlene rte of the present study rises the orreltion in Europe from r.45, p.225 to r.70, p.061. Seond, our dt re in line with the lrge differenes etween the prevlene rtes in Europe nd in the USA. A potentil risk to ll prevlene studies is the influene of nonresponders. Although the nonresponse in this study (47.4%) is higher thn in surveys employing telephone interviews, in whih nonresponse is redued y rediling, the ove results indite tht the study hs not suffered more from this soure of is thn other prevlene studies. Sesonl Vrition nd Influene of Month of Completion Severl uthors hve emphsized tht mood flutution over the sesons is not only present in SAD, ut is with smller mplitude lso present in norml sujets s well (Termn 1988; Thompson et l 1988; Wirz-Justie et l 1992). The present study onfirms these findings. Sujets with sesonl prolems differed from sujets without in the higher level of hnge they experiened over the yer on the six sesonlity items, ut not in the order of severity with whih the vrious items ontriute to the sesonlity sore (Figure 4). These dt re, like the dt from other studies, retrospetive in nture. As fr s we know, this is the first study in whih the influene of seson on mood is mesured diretly eh month in the generl popultion. Results show tht there is ler sesonl pttern, with pek in Deemer. The mximum differene of 4 points implies n inrese of lmost 50% of the men in Deemer ompred to July. This result onfirms the notion tht sesonl sensitivity is norml phenomenon, whih is experiened in n extreme wy y SAD sujets (f. Estwood et l 1985; Loste nd Wirz-Justie 1989). An importnt methodologil spet is tht in prevlene studies on depression in the generl popultion the seson in whih the study is performed is importnt nd should e tken into ount when interpreting the results. The CES-D dt strongly suggest tht the prevlene of depression in The Netherlnds is higher in winter thn in summer. Mood my influene sores on questionnires (f.

10 SAD in The Netherlnds BIOL PSYCHIATRY 1021 Hirshfeld et l 1983). Although GS sores seemingly were influened y ompletion in the different sesons, mood did not explin this vrine. The influene of month of ompletion on prevlene ws negligile, however, due to the other riterion of SAD, prolems with the sesons, whih ws not ffeted y month of ompletion. This finding supports this spet of the reliility of the SPAQ riteri for SAD. Epidemiologil Chrteristis Younger women re more sensitive to sesonl hnges thn older women nd men. Forty-one perent of the women who met the SAD riteri were etween 26 nd 35 yers of ge, whih is in line with other prevlene studies. Level of edution nd ivil sttus were unrelted to SAD. Winter depression is disling ondition, s shown y the higher perentge of sujets who re unemployed or on sik leve for long period of time. Of sujets with pying jo, onsiderle proportion reported sene from work. Sine these figures re sed on self-report only nd rely hevily on the reolletion of the respondents, they n merely e interpreted s inditive for the possile soioeonomi onsequenes of SAD. Some interesting findings emerged from the dt on the help sujets reeived for their sesonl prolems. A smll minority of the responders in the SAD group reeived help from medil speilists. Medition lrgely presried y generl prtitioners ws the tretment of hoie in 60.7% of SAD sujets. Remrkly, 41.1% of sujets with winter depression reeived help from linil psyhologists, lthough this profession rrely pplies light tretment in The Netherlnds, or presries medition. As expeted, the results show tht sujets meeting the SAD nd S-SAD riteri sleep more in utumn nd winter nd show more weight flutution during the ourse of the yer. In winter, women who meet the SAD riteri weigh more thn women who do not meet these riteri. The sme result ws found when SAD ptients were ompred to ulimi ptients nd norml ontrol sujets (Lm et l 1991). Mesured in the winter, SAD ptients reported weighing signifintly more thn the other two groups. In the present study, women of the SAD group who ompleted the questionnire in the summer were still slightly hevier thn women in the other groups, ut the differene did not reh signifine. Environmentl Ftors In study y Wirz-Justie et l (1990), omprison etween light tretment nd 1-hour outdoor wlk in the morning showed oth interventions to e eqully effetive. The uthors onluded tht sesonl prolems my e influened y tul exposure to outdoor light. The present study investigted whether the numer of hours spent outdoors in the different sesons ws onneted with SAD. It ws hypothesized tht winter depressives spend less time outside in the winter. Surprisingly, women in the SAD nd the S-SAD group did not differ in this respet from those in the NSAD group in winter, ut insted spent more time outdoors in summer. If time spent outdoors hs ny influene in SAD, the ontrst etween summer nd winter exposure to light my e ritil, rther thn the solute mount of light reeived in winter. Sujets meeting the riteri of SAD or S-SAD re more sensitive to wether onditions thn sujets in the NSAD group. This is the se for ll wether onditions exept high pollen ount. SAD nd Depression Aording to depression sores when ompleting the questionnires, sujets with winter depression were more depressed, with 63.4% of winter depressives meeting the riteri for possile seness (CES-D 16). This is not only the se in the winter months. An unexpeted finding ws tht winter depressives who filled out the questionnire in summer months (June, July, August), the time of yer they ought to feel good, hd high CES-D sores. Sixty perent of these 16 sujets met riteri for possile sesness. Moreover, 88.7% of sujets who reported hving sesonl prolems, nd 100% of sujets meeting riteri for winter SAD, stted tht they hd hd t lest one depressive episode in the lst 5 yers, independent of the sesons. Severl longitudinl studies (Leonhrdt et l 1994; Skmoto et l 1995; Shwrtz et l 1996; Thompson et l 1995; Wiki et l 1992) hve shown tht sujets with dignosis of SAD hve hnging pttern of depressive episodes in the ourse of their illness. Between 59.8% nd 74% of ptients with n initil dignosis of SAD in these studies did not fulfill the riteri of this disorder severl yers lter. SAD hd either fully remitted, or the pttern of depressive mood ws not sesonl nymore. Although these longitudinl studies my e influened y tretments sujets reeived (in most ses ntidepressive medition nd/or light tretment), results suggest tht the dignosis of SAD is not very stle over time. This onlusion is lso suggested y two studies (Murry et l 1993; Wirz- Justie et l 1993) of test retest reliility of the SAD dignosis using the SPAQ. Of sujets who met the SAD riteri, 41.4% nd 50%, respetively, were not dignosed s suh t the seond ssessment. In view of the long period etween ssessments, this result my e explined y the stility of the dignosis rther thn y the reliility of (the riteri of) the SPAQ. It is possile tht sujets suffering from SAD re lwys more vulnerle

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