Incidence of eating disorders in Navarra (Spain)

European Psychiatry 20 (2005) 179 185 http://france.elsevier.com/direct/eurpsy/ Original article Incidence of eating disorders in Navarra (Spain) Francisca Lahortiga-Ramos a, *, Jokin De Irala-Estévez b, Adrián Cano-Prous a, Pilar Gual-García c, Miguel Ángel Martínez-González b, Salvador Cervera-Enguix a a Department of Psychiatry and Medical Psychology, University Clinic, University of Navarra Medical School, Avda. Pío XII, 36. 31008, Pamplona, Spain b Department of Epidemiology and Public Health, University of Navarra Medical School, Pamplona, Spain c Department of Psychology and Psychiatry, International University of Catalonia, Barcelona, Spain Received 26 February 2004; accepted 15 July 2004 Available online 02 November 2004 Abstract Purpose. To estimate the overall annual incidence and age group distribution of eating disorders in a representative sample of adolescent female residents of Navarra, Spain. Methods. We studied a representative sample of 2734 adolescent Navarran females between 13 and 22 years of age who were free of any eating disorder at the start of our study. Eighteen months into the study, we visited the established centers and the eating attitudes test (EAT-40) and eating disorder inventory (EDI) Questionnaires were administered to the entire study population. We obtained a final response of 92%. All adolescents whose EAT score was over 21 points and a randomized sample of those who scored 21 or below, were interviewed. Any person meeting the DSM-IV diagnostic criteria for Anorexia Nervosa (AN), Bulimia Nervosa (BN) or eating disorder not otherwise specified (EDNOS) was considered a case. Results. We detected 90 new cases of eating disorders. Taking into consideration the randomly selected group whose EAT score was 21 points or below, we estimated the overall weighted incidence of eating disorders to be 4.8% (95% CI: 2.8 6.8), after 18 months of observation, in which EDNOS predominated with an incidence of 4.2% (95% CI: 2.0 6.3). The incidence of AN was 0.3% (95% CI: 0.2 0.5), while that of BN was also found to be 0.3% (95% CI: 0.2 0.5). The highest incidence was observed in the group of adolescents between 15 and 16 years of age. Conclusions. The overall incidence of ED in a cohort of 2509 adolescents after 18 months of follow-up was 4.8% (95% CI: 2.8 6.8), with EDNOS outweighing the other diagnoses. The majority of new cases of eating disorders were diagnosed between ages 15 and 16. 2004 Elsevier SAS. All rights reserved. Keywords: Eating disorders; Anorexia Nervosa; Bulimia Nervosa; Esting disorders not otherwise specified; Incidence; Eating attitudes test 1. Introduction Among the mental disorders, eating disorders (ED) have gained exceptional importance in recent decades, as evidenced by the numerous studies related to these diseases. This interest is stimulated by the need to prevent, to early detect and to effectively treat a group of disorders that affect a large population sector. A variety of factors including personality, genetic inheritance, neurobiological alterations and the mass media s portrayal of thinness as an attractive quality, all play a role. European and North American screening studies for * Corresponding author. E-mail address: flahortiga@unav.es (F. Lahortiga-Ramos). ED have found that between 10% and 25% of adolescents scored above the limit for ED in a variety of questionnaires aimed at detecting ED [1]. In addition, it is estimated that Anorexia Nervosa (AN) and Bulimia Nervosa (BN) affect approximately 1.2 million women in the US [10], occupying the third cause of illness in the young population after obesity and asthma [26]. These disorders present a chronic course, an elevated morbidity [25] and a mortality ranging from 6% to 15% [8,17,29]. Discrepancies are observed in data from incidence and prevalence studies on ED conducted over the recent years. This could be due to different methodological problems [9], such as the use of large-scaled psychiatric databases, the low positive predictive value and low validity and transcultural 0924-9338/$ - see front matter 2004 Elsevier SAS. All rights reserved. doi:10.1016/j.eurpsy.2004.07.008

180 F. Lahortiga-Ramos et al. / European Psychiatry 20 (2005) 179 185 reliability of self-reported questionnaires for screening ED, the shortage of confirmatory interviews and the limitations of the standardised diagnostic criteria. Despite some authors claims [9,32] that there is no clear evidence of a growing incidence of AN, the majority of incidence studies on ED suggest high numbers of new AN cases among the female adolescent population [18,27,31,39]. Currently, the incidence of AN in recent studies of general populations is around 100 cases/100,000/year in women aged 20 32 years [15]. The incidence of Bulimia Nervosa appears to be surpassing that of AN [26,30]. In the last decade, the incidence of BN has been 10 cases/100,000/year for all ages [19], and close to 500 cases/100,000/year in women between 20 and 32. This latter age group usually presents the highest number of cases of BN [15]. In recent years there has also been a growing interest in the study of disorders classified as Eating Disorders Not Otherwise Specified (EDNOS), whose frequency surpasses that of the full-syndrome eating disorders (AN and BN) [7,36], being even more common in the general population than among psychiatric patients [34]. Currently, the incidence of these disorders almost reaches 1000 cases/100,000/year in a sample of 826 Swedish women aged 20 32 years [15]; despite this fact, the relationship between these partialsyndrome eating disorders (PS-ED) and the full-syndrome eating disorders (FS-ED) is still unclear [4,25,40]. The objective of our study was to estimate the incidence of ED in a representative female adolescent population residing in the Autonomous Community of Navarra (Spain), after 18 months of follow-up. We also aimed to specifically estimate the incidence of EDNOS and to find the ages at which these disorders present with the highest frequency. 2. Methods Our study was conducted at the Department of Psychiatry and Medical Psychology of the University Clinic of the University of Navarra Medical School with the collaboration of the Department of Epidemiology and Public Health of the same university. We first conducted a prevalence study, the results of which have been published elsewhere [3]. Briefly, in the initial prevalence study, a weighted, random, multistage sampling scheme was used to select a representative sample of the female adolescent population (12 21 years of age) of Navarra (an autonomous region in the north of Spain with approximately 550,000 inhabitants). Informed consent forms to be signed by the parents were sent to the homes of the adolescents in the study. After the consent process, a specific date and time was set up for the participants to self-administer the ED screening tests (EAT-40 [13] and EDI [14]) at the school. Among 3472 girls aged 12 21 years who were invited, 2862 accepted to complete the baseline questionnaire (participation: 82.4%). After completing the initial screening questionnaire, participants with scores indicative of a possible ED were interviewed using a semi-structured interview performed by a psychiatrist experienced in ED and who applied DSM-IV criteria to diagnose Anorexia Nervosa (AN), Bulimia Nervosa (BN) or Eating Disorder Not Otherwise Specified (EDNOS). Only psychiatrist-confirmed diagnoses according to DSM-IV criteria were considered as prevalent cases. In this initial screening, 119 prevalent cases of ED (AN: nine cases; BN: 22 cases; EDNOS: 88 cases). Prevalent cases were then excluded for the subsequent follow-up analyses of this cohort in order to estimate the incidence of ED [3]. The results we are reporting in this paper are from the 18-month follow-up of this representative sample of female residents of the Autonomous Region of Navarra (Spain) where we excluded prevalent cases of ED. Since a psychiatric interview of all our sample was not possible nor efficient, and given our purpose was to detect the largest possible number of adolescents with ED and thus obtain as close to the true incidence as possible in our sample, the psychiatrists interviewed three groups of participants: all adolescents scoring above the cut-off value established by the creators of the questionnaire (EAT>30; where most cases were likely to be yielded) [12], those scoring over 21 points (to account for cases with borderline EAT scores), and a randomized sample of those scoring 21 points or below (to account for the very few possible cases with low EAT scores) [2]. The psychiatric assessment was blind with respect to screening status. The time and date were decided with the school directors for the administration of interviews at their respective schools. In the case of an adolescent s absence from school on the day chosen for interview, the interview took place at the Department of Psychiatry and Medical Psychology of the University Clinic. The adolescents who refused to be interviewed or did not show up for their appointment, were interviewed by telephone, and their responses were affirmed by those of close family members. Finally, on the adolescents who met the criteria to undergo an interview but explicitly refused to be interviewed, a presumptive diagnosis was made by psychiatrists based on the responses of these girls on the ED-specific questions of the EAT and EDI questionnaires. Frequency and central tendency measures were used to describe the sociodemographic characteristics of our sample. The estimation of incidences were performed taking into account the sampling scheme (only a sample of participants with EAT scores below 21 were interviewed by a psychiatrist), and therefore using a weighted analysis with weights equal to the sampling proportion. The statistical analysis was performed using the SPSS program version 10.1 and the Stata program 6.0. 3. Results The initial representative sample of adolescent participants in this study consisted of 2734 females between 12 and

F. Lahortiga-Ramos et al. / European Psychiatry 20 (2005) 179 185 181 21 years of age whose ages ranged 13 22 after the 18-month follow-up. Despite repeated attempts by telephone and by certified mail requesting their participation in the incidence study, 225 adolescents refused to participate, resulting in a final sample size of 2509 adolescents, and representing a 92% response rate. To evaluate the extent of a possible selection bias due to these non-participants we examined their EAT scores in the previous prevalence study. Indeed the non-participants had higher EAT scores than the participants. Twenty-three (10.2%) non-participants had EAT scores above 30 in the prevalence phase compared to 8.4% in this incidence study, 42 (18.7%) presented initial EAT scores between 22 and 30 compared to 9.3% in the incidence study and 160 (71.1%) had EAT scores below 22 in the prevalence study compared to 82.3% in the incidence study. We interviewed all adolescents whose EAT scores were above 21, in addition to a randomized sample of 64 adolescents (3%) scoring 21 points or lower. The total number of interviews to be administered was 508 (Fig. 1). All interviews were performed at least after 18 months of follow-up and there were no significant differences in follow-up warranting the use of person-time rates. The large majority (89.7%) accepted to be personally interviewed by a physician specialized in Psychiatry, 383 adolescents at their respective schools or at the Department of Psychiatry and Medical Psychology of the University Clinic, and 73 adolescents by telephone. The responses of the latter were confirmed by those of other family members. Among the 508 planned interviews, 52 adolescents (10.2%) could not be interviewed by the research physicians (34 who could not be located and 18 who explicitly refused to continue in the study). We chose not to exclude these girls to avoid a selection bias and rather chose to perform a sensitivity analysis with their presumptive diagnoses. The majority of adolescents (2065; 82.3%) scored 21 points or below on the EAT questionnaire. Two hundred and thirty three participants (9.3%) scored between 22 and 30 points, while slightly fewer adolescents (n = 211; 8.4%) scored above 30 points on the questionnaire (Fig. 1). The average age of the adolescents studied was 16.4 years (standard error: 0.05). The majority of them were the youngest of siblings, lived with their parents in an urban environment and considered the socioeconomic status of their family to be middle-high. Only 2% of the adolescents referred having a history of a parent or sibling presenting an ED (Table 1). The average Body Mass Index (BMI) was 21.6 kg/m 2 (95% CI: 21.5 21.7), the minimum weight over the last month being slightly higher than the weight considered to be ideal by the adolescents (Table 1). The average total score obtained on the EAT was 14.5 points, with values ranging between 0 and 88 points. On average, the adolescents scored lowest on the Bulimia and Interpersonal Distrust subscales of the EDI, and highest on the Body Dissatisfaction and Maturity Fears subscales (Table 2). In our study, 90 new cases of ED were detected out of 2509 adolescents. As mentioned in Section 2, the following incidence rate estimates are weighted incidences taking into account the sampling scheme used to confirm the diagnoses. The overall 18-month incidence was therefore 4.8% (95% CI: 2.84 6.82) in other words 3200 cases/100,000/year, with EDNOS leading with an 18-month incidence of 4.2% (95% CI: 2.04 6.34) or 2800 cases/100,000/year. The 18-month incidence of AN was 0.3% (95% CI: 0.16 0.48) or 200 cases/100,000/year, all of them belonging to the restrictive subtype. The incidence of BN was also 0.3% (95% CI: 0.15 0.49) or 200 cases/100,000/year, and only one case belonged to the non-purging subtype (Table 3). Subtype 4 of EDNOS (inappropriate compensatory behaviours), was the most frequent diagnosis, with 39 cases, and an incidence of 2.8% (95% CI: 0.15 5.75) or 1867 cases/100,000/year. Fewer cases (n = 14) during the 18-month follow-up (0.6%, 95% CI: 0.16 0 96) or 400 cases/100,000/year were found for subtype 6 (binge-eating disorders). No cases for subtype 5 (chewing and expulsion of food) were detected (data not shown). Fig. 1. Distribution of Eating Attitudes Test scores and diagnoses of representative sample of adolescent residents of Navarra.

182 F. Lahortiga-Ramos et al. / European Psychiatry 20 (2005) 179 185 Table 1 Sociodemographic and anthropometric characteristics of the study population at the beginning of the study Sociodemographic variables N % Birth place Navarra 2053 81.8 Other 449 17.9 No response 7 0.3 Location of residence Urban 1278 51.0 Rural 1216 48.5 No response 15 0.5 With whom the adolescent lived Family 2169 86.4 Other 336 13.4 No response 4 0.2 Civil status of parents Married 2272 90.6 Separated-divorced 137 5.5 Other 93 3.7 No response 6 0.2 Socioeconomic status of parents Middle-high 2349 93.6 Midde-low 98 3.9 No response 62 2.5 Adolescent s place in sibling order Eldest 988 39.4 Middle 375 14.9 Youngest 1045 41.7 No response 101 4.0 Parents or siblings in psychiatric treatment No 2368 94.4 Yes 114 4.5 No response 27 1.1 Parents or siblings with ED No 2417 96.3 Yes 50 2.0 No response 42 1.7 Anthropometric variables Mean 95% CI Range BMI 21.6 21.5 21.7 11.7 42.1 Kg lost by dieting 4.1 3.9 4.3 0 22 Minimum weight 51.0 50.7 51.4 24.0 85.5 Maximum weight 55.5 55.2 55.9 27 100 Ideal weight 50.8 50.6 51.1 28 72 CI: Confidence interval. Table 2 Mean scores on each factors of the Eating Attitudes Test and each subscales of the Eating Disorder Inventory Questionnaires found in girls of the Incidence study Mean scores 95% CI a Range b EAT factors Factor 1 (dieting) 5.2 5.0 5.4 0 36 Factor 2 (bulimia) 0.4 0.3 0.4 0 22 Factor 3 (oral control) 2.5 2.3 2.6 0 21 Total EAT Score 14.5 14.1 14.9 0 88 EDI subscales Drive for thinness 4.4 4.2 4.6 0 21 Bulimia 1.0 0.9 1.1 0 22 Body dissatisfaction 7.9 7.6 8.2 0 27 Ineffectiveness 3.0 2.8 3.1 0 29 Perfectionism 4.6 4.4 4.7 0 38 Interpersonal distrust 2.6 2.5 2.7 0 20 Interoceptive awareness 3.5 3.4 3.7 0 27 Maturity fears 4.7 4.6 4.9 0 24 a CI: Confidence interval. Ranges in study sample. We observed a rather homogeneous distribution with respect to age of presentation of ED, although there were two peaks in incidence: one at 15 and 16 years of age (9.4%; 95% Table 3 Incidence of Eating Disorders during the 18 months of follow-up Diagnosis (DSM-IV) Cases 18-month incidence% (95% CI) Anorexia Nervosa 8 0.3 (0.16 0.48) Bulimia Nervosa 8 0.3 (0.15 0.49) EDNOS 74 4.2 (2.04 6.34) Total (AN, BN, EDNOS) 90 4.8 (2.84 6.82) CI: Confidence interval. CI: 0.3 18.5) and another peak at >18 years of age (4.5%; 95% CI: 0.6 8.4) (Table 4). An analysis of the age distribution of the different ED subtypes (Table 4) shows that the highest incidence was observed for EDNOS corresponding to the age group between 15 and 16 years (8.7%; 95% CI: 0.0 17.7). No marked differences were observed in the incidence values for AN between the different age groups. For BN however, there were no cases among the older adolescents, which is not consistent with the general belief, in clinical practice, that these disorders usually present during or after late adolescence (Table 4).

F. Lahortiga-Ramos et al. / European Psychiatry 20 (2005) 179 185 183 Table 4 Incidence of Eating Disorders by age Diagnosis (DSM-IV) AGE % 95% CI Anorexia Nervosa 13 14 0.2 0.0 0.4 15 16 0.4 0.0 0.9 17 18 0.5 0.0 1.1 >18 0.4 0.0 1.4 Bulimia nervosa 13 14 0.3 0.0 0.7 15 16 0.3 0.0 7.0 17 18 0.5 0.0 1.1 >18 0.0 0.0 0.0 EDNOS 13 14 2.2 1.1 3.2 15 16 8.7 0.0 17.7 17 18 2.5 0.6 4.4 >18 4.0 0.4 7.7 Total (AN, BN, EDNOS) 13 14 2.7 1.4 3.9 15 16 9.4 0.3 18.5 17 18 3.4 1.1 5.8 >18 4.5 0.6 8.4 CI: Confidence interval. 4. Discussion As affirmed by Garfinkel [11], the main objective of epidemiological studies is to collect the necessary data for rational and effective health care programming. Our investigation is the first in Spain to study the incidence of ED in a representative sample of a target adolescent population of a whole region. A weighted, random, multistage sampling scheme was used to select a representative sample from a school-aged population of Navarra during the 1997 98 academic year. The schooling rate was high, since those between 3 and 18 years of age not attending school represented only 5% of this population. We used a screening questionnaire (EAT-40) and a confirmatory diagnostic interview to ascertain our ED cases. Interviews and diagnoses were performed only by two physician psychiatrists to reduce diagnostic variability as much as possible. Both psychiatrists were specifically trained to perform the interviews by one same senior psychiatrist with experience in ED and during the six-month period previous to the beginning of the study. The training focused mainly in making the interview method and procedure homogeneous and, at the end of their training, both interviewers were evaluated by a second senior psychiatrist. Finally, the interviews were performed individually with each adolescent, most interviews in their own educational center and clearly informing on confidentiality. The range of ages of the female participants in this incidence study (13 22 years of age), was appropriate to our goals since the age of onset for ED is generally accepted to be between ages 10 and 19 [25,33], and because ED are 10 times more frequent in women than in men [20,35,38]. The incidence of AN from our study (200 new cases/100,000/year) was higher than the majority of values cited in preceding studies; this incidence is very different from what is observed in the epidemiological studies on ED first conducted in the 1970 s using case registries from a specific area of the countries studied and including all ages [23,37]. These figures are not so different from the late 1980s and especially the 90s in studies conducted using local hospital and primary health care case registries [5,16,24, 27,28,30]. The incidence of AN during these decades was 10 times lower than what was found in our population. An exception to this statement can be observed in the Swedish study by Ghaderi and Scott [15], in which after 2 years of following 826 women between 20 and 32 years of age, incidence values for AN were higher (100 new cases/ 100,000/year) than those found in earlier studies, but were rather close to ours. Perhaps the similarity in study methods used in both the Swedish study and in ours, is the reason for these similar findings of incidence. The lower values obtained by Ghaderi and Scott could be related to several issues such as their smaller sample size, the longer follow-up period, the lower response rate, and the age range of their sample. Despite the data by Garner and Fairburn [13] using data from the general population, which showed an increase in diagnoses of BN after it was considered a real disease, the incidence values for BN described until now have been very low in studies conducted using all ages and mainly hospital case registries, compared to those of our study [5,35,38]. Our incidence rate for BN (200 new cases/100,000/year) is similar to what we found for AN. Ghaderi and Scott [15] found values higher than ours, describing an incidence of BN close to 500 new cases/100,000/year. This difference can most likely be attributed to the age range studied by these authors (20 32 years); most authors agree that an increase in BN is seen in later ages. This would explain the higher incidence of BN found in Ghaderi and Scott s study in comparison to ours. Comparing our results to those of previous studies is somewhat more difficult for EDNOS. Despite various authors claims that EDNOS are more common than the classic ED, many of the former even remaining undiagnosed [36] and that EDNOS are more frequent in the general population than in the psychiatric population [34], further studies are necessary to confirm these statements. In our study, we found 2800 new cases/100,000/year, a value higher than the one obtained for AN and BN, and than figures of studies performed with samples of patients with ED [16,22]. Patton et al. [31] found an incidence for EDNOS similar to ours (2180 new cases/100,000/year) after studying a school-aged population of 14 15 years of age over a 3-year period. Ghaderi and Scott [15] found the incidence to be 960 new cases/100,000/year. Again, these differences can be due to the age range studied by the authors (20 32 years) and to the longer follow-up period (2 years), which probably enabled EDNOS cases to become cases of BN. If EDNOS indeed are previous stages of more specific ED, a longer follow-up period of the patients that are at the moment classified as presenting ED of an unspecified type could very well end-up becoming more specific cases of ED such as AN and BN. The fact that the only incidence value higher than ours in this Swedish study was for BN, supports this belief. As seen in other psychiatric disorders, the onset of ED is subtle,

184 F. Lahortiga-Ramos et al. / European Psychiatry 20 (2005) 179 185 symptoms appear gradually, and all criteria for AN or BN are met only after a certain period of time during which the illness has progressed [21]. During a short follow-up period, like the one in our study, we would more easily detect those eating disorders of lesser severity that may not meet all the diagnostic criteria but that might later develop into a fullsyndrome ED. The excessively strict and somewhat arbitrary diagnostic criteria for AN and BN [21] may also be a factor for yielding more EDNOS type ED in studies with shorter follow-up periods. The relatively high incidences of ED found in this investigation as well as in other studies conducted at the end of the last century, could be due to the increase in health services with clinics specially designed for the study, diagnosis and treatment of these disorders. In addition, there is a larger social awareness to confront these types of eating disorders, probably due to the high morbi-mortality rates associated to them (5 15% [29]). Finally, a decrease in the stigma associated with psychiatric disease in general, and the better access to mental health centers also contribute to an earlier detection of these cases. Another important fact to take into account when considering the generalizability of our data is the age range of our study participants. They were in general younger than other studies reviewed and thus presented incidences reflecting the higher rates usually found in these ages compared to rates in older subjects. In spite of all of these uncertainties, we believe that an early detection of these problems is in itself beneficial. The predominance of new cases in the mid-adolescent period detected in our study reveals the precocious appearance of this disease. This would challenge Pawluck and Gorey s [32] affirmation that while there was an increase in frequency of this disease in the later years (20 30 years), the incidence of the disease in the early adolescent period remained constant. As for BN, the elevated incidence found in our study in the age group of 17 18 years could be explained by the difficulty in following-up our group of university students (females over 18 years of age). It is also possible that we observed more subtle symptoms which only partially fulfilled the diagnostic criteria, thus generating an EDNOS as the diagnosis. In any event, the age of onset of the new cases in our sample, being earlier than in other studies, as well as the predominance of EDNOS as the diagnosis, lead us to believe that both AN and BN actually might begin presenting themselves as incomplete syndromes, and after an undetermined period of time, develop into full disease. Although the follow-up rate in our study (92%) was higher than that of other studies [6,15,31], we conducted a small comparative analysis between the group of adolescents that had answered the questionnaire and who agreed to carry on with the incidence study, and the group of those who refused to continue in the study we are now reporting. The adolescents who had not answered the questionnaire, weighed more and had a higher minimum and maximum weight and BMI than those in the group that did answer, according to the prevalence study conducted 18 months earlier. This challenges the likelihood of the presence of at least AN cases in these non-responders. By age groups, the follow-up was 95.1% (age group 13 14), 94.6% (age group 15 16), 89.2% (age group 17 18), 86.5% (age group >18). Indeed the lowest proportion was in the >18 age group as expected due to frequent address changes in this group mostly comprising university students. However, proportions can be considered consistently high over all groups. In addition, we compared the EAT scores from the previous prevalence study [3] with the scores obtained on the same questionnaire in this incidence study to rule out a selection bias due to the non-participation of some adolescents. We observed that the adolescents who did not participate in this incidence study scored higher. As mentioned above, EAT scores were higher in non-participants than in participants and the largest difference in EAT scores between nonparticipants and participants was in the group with EAT scores between 22 and 30 (18.7% of non-participants versus 9.3% in participants were in this EAT scoring group). There is therefore some evidence that non-participants might have presented proportionally higher incidence rates of ED than participants, had they participated. If we apply the rates expected in each of the three EAT groups studied (<22, 22 30 and >30), to the three EAT groups of non-participants we could hypothesize that we would have found around 12 additional cases, had there been a 100% participation rate. This would have probably increased our 18-month estimate of ED incidence from 4.8% to 5% (i.e. from 3200 cases/ 100,000/year to 3333 cases/100,000/year). This possible participation selection bias, in any case, results in a slight underestimation of an incidence rate that in itself warrants public health attention. Ten out of the 52 adolescents who refused to be interviewed, were diagnosed with ED after psychiatrists analyzed their responses to the questionnaires and tried to apply DSM-IV diagnostic criteria to reach a presumptive diagnosis. Had these cases not diagnosed using the semistructured interview with a psychiatrist been excluded from the analysis, the overall incidence of ED would have been 4.4% (95% CI: 2.02 6.88), slightly lower than the overall incidence (4.8%) obtained when included. There is therefore no evidence of bias when performing this sensitivity-type analysis. Both incidence rates are important enough to deserve special public health attention and do not have values far away from each other. Conversely, had these adolescents without an interview experienced a higher incidence rate of ED, we would be underestimating an incidence rate that is important as it is, without the correction. In this research study we have tried to overcome some of the methodologic problems observed in other incidence studies regarding ED [20,22,23,27,30,32] in order to obtain incidence rates of ED in our population as close to the real value as possible. There are authors who support an increased incidence of ED among older female adults [32], and others that even

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