Prevalence and Correlates of Erectile Dysfunction in a Population-based Study in Belgium

European Urology European Urology 41 2002) 132±138 Prevalence and Correlates of Erectile Dysfunction in a Population-based Study in Belgium Rudolf Mak a,*, Guy De Backer a, Marcel Kornitzer b, Jean Marie De Meyer c a Department of Public Health, Ghent University, De Pintelaan 185, 9000 Ghent, Belgium b School of Public Health, Universite Libre de Bruxelles, Brussels, Belgium c Department of Urology, Jan Pal jn Hospital, Ghent, Belgium Accepted 12 September 2001 Abstract Objectives: This study aims to estimate the prevalence of erectile dysfunction ED) in the male population of Belgium, and to study its correlation with education, the international prostate symptom scale IPSS), sexual activity, depression, body mass index, alcohol, smoking, easiness to discuss ED with a doctor, current health index, physical activity, hypertension, diabetes, cardiovascular disease, professional status, residence and whether or not the respondent lives alone. Methods: An age-strati ed random sample of the male population aged 40±70 years of Ghent and Charleroi was interviewed in the home by a trained, experienced male nurse, using a structured interview that included the international index of erectile function IIEF) and the IPSS. ED was classi ed by the subjects' self-reported con dence to achieve and maintain an erection. Results: In total, 799 men were interviewed, with a participation rate of 38.0%. The overall age-adjusted prevalence of ED was 10.1% severe, 24.7% moderate, 26.6% mild, and 38.7% reported no ED. Age and the absence of sexual activity over the last 4 weeks were the strongest correlates of ED. Other strong correlates were four or more health complaints, depression, a high score for the IPSS and absence of physical activity. Discussion: The prevalence of ED in Belgium is comparable with the results of other population-based studies for severe and moderate ED. Sexual inactivity over the last four weeks is a strong correlate of ED, and should make the clinician think of a possible problem of ED. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Erectile dysfunction; Prevalence; Correlates; Belgium 1. Introduction Estimating the prevalence of erectile dysfunction ED) is important for doctors and patients to decide whether it is a rare or a common condition. If common, doctors may be more motivated to discuss ED with elderly men, and patients may be comforted by the idea not to be alone with the problem. However, this estimation creates several methodological problems. Results of studies in clinical populations cannot be extrapolated to the general population. Population * Corresponding author. Tel. 32-9-2403616; Fax: 32-9-2404994. E-mail address: rudolf.mak@rug.ac.be R. Mak). studies are rare, and in many populations ED still is a taboo subject. Many men will not easily reveal problems with sexual performance. Biased selection of participants in a population-based study is therefore dif cult to avoid. However, if we assume that men with sexual problems are less likely to participate in surveys, the likelihood is that these surveys will underestimate the true prevalence. This study will add data to prevalence studies in other geographic areas [1±3]. Knowledge of the correlates of ED may be helpful in detecting ED in an early phase. It will also give the clinician a better idea of which concurrent conditions such as diabetes and cardiovascular disease) may accompany ED. 0302-2838/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S0302-2838 01)00029-X

R. Mak et al. / European Urology 41 2002) 132±138 133 2. Methods In order to obtain a sample representative of the cultural diversity of Belgium, we used a randomly selected age-strati ed 40±49, 50± 59, 60±69 years) sample from the of cial register of the male population of Ghent Flemish community) and Charleroi French community), two comparable middle-sized Belgian urban areas with approximately 250,000 inhabitants each. The study was conducted from April 1999 to December 1999. Potential subjects were sent an invitation letter and asked to return a postage-paid reply form. Those who did not reply within three weeks were contacted via telephone by an interviewer, or sent a mailed reminder if they had no telephone. Sampling was continued till we reached the target of 800 participants. Having arranged an appointment, the interviewers four male nurses in Ghent, and one male nurse with experience in previous studies in Charleroi) conducted a personal interview with a standardised questionnaire, containing sets of questions regarding the possible correlates of ED and prostate problems, including questions regarding: age, marital status, education, occupational status, smoking, consumption of alcohol and coffee, physical activity, height, weight, blood pressure, diabetes, cholesterol, history of hospitalisation for cardiovascular diseases, neurologic disorders, cancer, surgical procedures, use of medication, depression, healthðwell being scale, life events and coping. To evaluate lower urinary tract symptoms, we used the international prostate symptom scale IPSS) [4]. Information regarding erectile function was obtained using the international index of erectile function IIEF) [5]. Comfort when talking about sensitive problems and access to appropriate health care were assessed as well by the nurse-interviewer. All data were reported by the respondent, no clinical examination was performed. Since a high proportion of men, especially in the higher age groups, were not sexually active in the last 4 weeks, giving a score of less than 6 in the erectile function domain scale EFDS) of the IIEF, we used question 15 how do you rate your con dence that you could get and keep an erection?) of the IIEF, as a surrogate measure of ED. Very high con dence was considered always achieving/maintaining an erection no ED), high con dence most times able to achieve/maintain an erection mild ED), moderate and low con dence sometimes achieving/maintaining an erection moderate ED) and very low con dence never achieving/maintaining an erection complete ED). In order to make the study more comparable to other studies, we also introduced an additional question, asking men to categorise themselves in four classes: always able to get and maintain an erection, usually, sometimes and never [6]. Since this question was only introduced after the beginning of the study, only 291 men gave an answer. In order to study the correlates of ED, we operationalised the variables as follows: ED: For the dependent variable, we considered no and mild ED as a negative history of ED score 0), and moderate and severe ED as a positive history of ED score 1). IPSS: The cut-off value of 7 was used to dichotomise the IPSS. A value 1 was given to the men with a score of more than 7 and 0 to those with 7 or less. Sexual activity: A score of 1 is attributed to those not active over the last 4 weeks, and 0 to the active. Education: Men with a low education <11 years) scored 2, men with further education 11±15 years) 1, and men with higher education >15 years) 0. Depression: On the depression scale based on modi ed CES-D) [7,8] with a range of possible scores 18±54, the upper quartile of men p75-score ˆ 28) scored 1. For the lower three quartiles a value of 0 was given. Body mass index: The body mass index is de ned as the weight in kilogram divided by the square length in meters. We used the cut-off of 27 to split the sample. A value of 0 was given to those with a BMI of 27 or lower, and of 1 for those who have a higher index. Alcohol: Alcohol consumption was measured in gram per day. Less than 20 g per day two drinks a day) scored as 0, 20±40 g per day scored 1, and more than 40 g per day scored 2. Cigarette smoking: Those who never smoked score 0, those who ever smoked but stopped scored 1 and current smokers 2. Willingness to discuss ED with the doctor: Answer to the question: if the doctor does not ask for it, would you tell him if you had problems with erectile function? If yes, a score of 0 was attributed, and if maybe or no, a score of 1. Current health index: The current health index is the result of a set of 13 questions [9] regarding health complaints. An index of 3 or less median) scored as 0, and more than 3 as 1. Physical activity: If the physical activity is high more than once a week 20 min of exercise), the score is 0. A low activity level scored 1. Hypertension: If a health care worker ever told the respondent, he had high blood pressure, the score is 1, if not, 0. Diabetes: If a health care worker ever told the respondent, he had diabetes, the score is 1, if not, 0. History of cardiovascular diseases: Hospitalisation for cardiovascular reasons or a positive questionnaire for angina [10] scored 1, if not 0. Professional activities: Current employment scored 0, and all other categories 1. In statistical analysis, prevalence estimates for the total population of men from 40±70 years were age standardised direct standardisation) to the current male population of Belgium population data as of 1 January 1999). Logistic regression was used to calculate the odds ratios OR) for each potential correlate with ED as the dependent variable no or mild ED versus moderate or severe ED). 3. Results In total, 2508 invitation letters were sent out. A total of 1615 men were contacted, of whom 799 agreed to be interviewed. Those who could not be contacted had moved from the area, were deceased, or incapable of being interviewed 428), or did not reply to the reminder and could not be contacted by telephone 465). Thus, the response rate was 1615/2080 ˆ 77:6% and the participation rate among the respondents was 799/ 1615 ˆ 49:5%. The overall participation rate was 38%. Participation was highest in the age group 60±69 years: 44.0%, in both other strata it was 35.6%. The characteristics of the population are summarised in Table 1. The majority of the men live with their partner. More than 50% were no longer actively employed, mostly because of retirement. Ghent and Charleroi provided an equal number of participants. In Table 2, we present the EFDS of the IIEF. For 14 men, data were missing. There was a very strong relation between age and EFDS-score. No sexual

134 R. Mak et al. / European Urology 41 2002) 132±138 Table 1 Characteristics of the study population of 799 men in Belgium Number % Age group 40±49 years 247 30.9 50±59 years 247 30.9 60±69 years 305 38.2 Marital status Married 607 76.0 Divorced 112 14.0 Single 56 7.0 Widowed 24 3.0 Living conditions Lives together with partner 645 80.7 Lives with other than partner 25 3.1 Lives alone 129 16.1 Professional status Employed 338 42.3 Unemployed 50 6.3 Retired 267 33.4 Other a 144 18.0 Residence Ghent 406 50.8 Charleroi 393 49.2 a Early retirement, sick leave, temporary unemployment. activity in the last 4 weeks was reported in 8.3% of men in the age group 40±49 years, in 21.7% of men 50±59 years and 47.8% in the men in the age group 60±69 years. A high score of >25 on the EFDS, indicating no ED according to the IIEF, was observed in 80.9% of the younger men, 60.2% of the men in the middle group, and in 34.1% of the men 60±69 years. In the youngest age groups, the likelihood of being sexually active was signi cantly lower in men living alone. This difference was still present in the oldest group, but without reaching statistical signi cance. In total, 291 men answered to the extra question categorising men in four classes of ED, according to their own opinion. If we correlate the new question with the IIEF 15 question con dence in getting and maintaining an erection), the weighted kappa statistic is 0.61 0.54±0.68) 95% CI con dence intervals)). In Table 3, we give the percentages with the 95% con dence intervals of ED, de ned as lack of con- dence in getting and maintaining an erection, in three age groups. Data were missing for 9 men. Severe ED was reported by 24.5% of the men 60±69 years, 9.4% of those 50-59 years and only 1.2% in the men between 40 and 49 years. Severe ED was reported by 12.7% of all men between 40 and 70 years in our study. Moderate ED was reported by 34.1% of the men 60±69 years, 33.1% of those 50±59 years and 11.9% in the man between 40 and 49 years. Moderate ED was reported by 27.6% of all men between 40 and 70 years in our study. Mild ED was reported by 22.9% of the men 60± 69 years, 26.9% of those 50±59 years and 29.6% in the man between 40 and 49 years. Mild ED was reported Table 2 EFDS of the IIEF in the study population of 799 men in Belgium EFDS 40±49 years 50±59 years 60±69 years Total <6 No sexual activity) 20 8.3%) 53 21.7%) 143 47.8%) 216 27.5%) 6±10 Severe ED) 1 0.4%) 5 2.0%) 8 2.7%) 14 1.8%) 11±17 Moderate ED 5 2.1%) 6 2.5%) 12 4.0%) 23 2.9%) 17-25 Mild ED) 21 8.7%) 33 13.5%) 34 11.4%) 88 11.2%) >25 No ED) 195 80.6%) 147 60.2%) 102 34.1%) 444 56.6%) Total 242 244 299 785 Table 3 Prevalence with 95%CI of ED defined as lack of confidence in getting and maintaining an erection) in three age groups of the study population of 799 men in Belgium Age group years) Total No ED Mild ED Moderate ED Severe ED Number % 95%CI) Number % 95%CI) Number % 95%CI) Number % 95%CI) 40±49 243 139 57.2 50.7±63.5) 72 29.6 24.0±35.8) 29 11.9 8.1±16.7) 3 1.2 0.3±3.6) 50±59 245 75 30.6 24.9±36.8) 66 26.9 21.5±33.0) 81 33.1 27.2±39.3) 23 9.4 6.0±13.8) 60±69 302 59 19.5 15.3±24.6) 66 22.9 17.4±27.0) 103 34.1 28.8±39.8) 74 24.5 19.8±29.8) Crude rate 790 273 34.6 31.3±38.0) 204 25.8 22.8±29.1) 213 27.6 23.9±30.2) 100 12.7 10.5±15.2) Age adjusted a 38.7 35.3±42.1) 26.6 23.5±29.7) 24.7 21.7±27.7) 10.1 8.0±12.2) a Population Belgium 1 January 1999.

R. Mak et al. / European Urology 41 2002) 132±138 135 Table 4 ORs for ED defined as lack of confidence in getting and maintaining an erection) and potential correlates in three age groups of 799 men in Belgium Correlate Value Age 40±49 years Age 50±59 years Age 60±69 years Score moderate, low or very low confidence %) Score moderate, low or very low confidence %) Score moderate, low or very low confidence %) Education High 10.5 11/105) 36.8 28/76) 52.8 28/53) Middle 10.9 7/64) 1.05 0.38±2.86) 41.3 19/46) 1.21 0.57±2.55) 53.6 45/84) 1.03 0.52±2.05) Low 18.9 14/74) 1.99 0.85±4.7) 46.3 57/123) 1.48 0.82±2.66) 63.0 104/165) 1.52 0.81±2.84) IPSS 7 12.4 27/218) 39.3 81/206) 53.7 122/227) >7 14.3 3/21) 1.18 0.33±4.27) 59.5 22/37) 2.26 1.11±4.62) 77.1 54/70) 2.90 1.57±5.38) Sexually active in last 4 weeks Yes 11.7 26/223) 32.3 62/192) 35.8 58/162) No 30.0 6/20) 3.25 1.15±9.19) 79.2 42/53) 8.01 3.86±16.61) 85.0 119/140) 10.12 5.78±17.86) Depression Low 3 quartiles 12.8 22/172) 38.0 70/184) 52.3 115/220) Highest quartile 14.3 10/70) 1.14 0.51±2.54) 55.9 33/59) 2.07 1.14±3.74) 75.3 58/77) 2.79 1.56±4.99) Body mass index <27 12.2 19/156) 42.7 61/143) 58.3 95/163) 27 14.5 12/83) 1.22 0.56±2.65) 42.0 42:100) 0.97 0.58±1.63) 57.9 77/133) 0.98 0.62±1.57) Alcohol <20 g per day 12.9 16/124) 41.5 49/118) 63.3 112/177) 20±40 g per day 11.5 7/61) 0.88 0.34±2.25) 27.5 14/51) 0.53 0.26±1.1) 45.6 31/68) 0.49 0.28±0.86) 40 g per day 15.5 9/58) 1.24 0.51±3.0) 53.9 41/76) 1.65 0.92±2.95) 59.6 34/57) 0.86 0.47±1.58) Smoking Non 18.5 12/65) 38.5 25/65) 57.6 38/66) Ex versus non) 8.2 7/85) 0.40 0.14±1.07) 30.9 25/81) 0.71 0.36±1.42) 59.9 85/142) 1.10 0.61±1.99) Current versus non) 14.6 13/89) 0.76 0.32±1.78) 54.2 52/96) 1.90 1.00±3.59) 57.8 52/90) 1.01 0.53±1.92) Information to doctor Yes 15.8 9/57) 36.3 61/168) 56.7 106/187) May be or no 12.0 22/184) 1.38 0.60±3.20) 56.6 43/76) 2.29 1.32±3.97) 61.6 69/112) 1.23 0.76±1.98) Current health index 3 4.9 6/122) 38.3 44/115) 44.6 70/157) >3 23.0 26/113) 5.78 2.28±14.65) 45.7 58/127) 1.36 0.81±2.27) 74.1 106/143) 3.56 2.18±5.80) Physical activity High 13.3 13/98) 29.7 22/74) 43.5 40/92) Low 13.1 19/145) 0.99 0.46±2.10) 48.0 82/171) 2.18 1.22±3.90) 65.1 136/209) 2.42 1.47±4.00) Ever told hypertension No 13.6 26/191) 39.5 64:162) 50.8 93/183) Yes 12.2 6/49) 0.89 0.34±2.29) 48.8 40/82) 1.46 0.85±2.49) 70.9 83/117) 2.36 1.44±3.87) Ever told diabetes No 12.6 30/239) 40.7 87/214) 58.1 151/260) Yes 50.0 2/4) 6.97 0.95±51.32) 54.8 17/31) 1.77 0.83±3.78) 61.9 26/42) 1.17 0.60±2.29) History cardiovascular disease No 13.7 28/204) 38.2 71/186) 50.8 93/183) Yes 10.3 4/39) 0.72 0.24±2.18) 55.9 33/59) 2.06 1.14±3.72) 70.6 84/119) 2.32 1.42±3.79) Professionally active Yes 9.1 18/197) 40.5 49/121) 37.5 6/16) No 30.4 14/46) 4.35 1.97±9.62) 44.4 55/124) 1.17 0.71±1.95) 59.8 171/286) 2.48 0.88±7.01) Residence Ghent 9.0 12/133) 42.3 44:112) 49.3 75/152) Charleroi 18.2 20/110) 2.24 1.04±4.82) 54.3 60/133) 1.27 0.77±2.12) 68.0 102/150) 2.18 1.37±3.48) Home Partner 12.4 25/201) 41.0 87/212) 59.0 148/251) Alone 16.7 7/42) 1.41 1.04±4.82) 51.5 17/33) 1.53 0.73±3.19) 56.9 29/51) 0.92 0.50±1.69) by 25.8% of all men between 40 and 70 years in our study. After direct standardisation to the population of Belgium in 1999, the prevalence of ED, according to our de nition, among men in Belgium was estimated as 10.1% of all men between 40 and 70 years with severe ED, 24.7% with moderate, 26.6% with mild and 38.7% with no ED. The bivariate association between ED and the possible correlates available in this study are presented in Table 4, strati ed by age. In Table 5, associations are given for all ages. All variables except for body mass index, smoking and living alone, were related to ED. Alcohol use showed a U-shaped relationship with ED, without reaching statistical signi cance. Age, sexual activity over the last 4 weeks, current health index, depression, a high IPSS-score and physical activity were the strongest correlates to ED. 4. Discussion This study was based on a random sample of 799 men from two cities in Belgium, representing the French and Flemish speaking communities. The response rate of 38.0% is comparable to what is achieved in other epidemiological studies in Belgium

136 R. Mak et al. / European Urology 41 2002) 132±138 Table 5 ORs for ED defined as lack of confidence in getting and maintaining an erection) and potential correlates in 799 men in Belgium, age adjusted Correlate Value Age 40±69 years Score moderate, low or very low confidence %), age adjusted Education High 28.6 67/234) Middle 36.6 71/194) 1.44 0.96±2.16) 1.05 0.68±1.64) Low 48.3 175/362) 2.33 1.64±3.3) 1.52 1.04±2.23) IPSS 7 35.3 230/651) >7 61.7 79/128) 2.95 2.0±4.36) 2.25 1.48±3.45) Sexually active in last 4 weeks Yes 25.3 146/577) No 78.4 167/213) 10.72 7.35±15.62) 7.26 4.89±10.78) Depression Low three quartiles 35.9 207/576) Highest quartile 49.0 101/206) 1.71 1.24±2.37) 2.05 1.43±2.93) Body mass index <27 37.9 175/462) 27 41.5 131/316) 1.16 0.88±1.56) 1.02 0.74±1.40) Alcohol <20 g per day 42.2 177/419) 20±40 g per day 28.9 52/180) 0.56 0.38±0.81) 0.56 0.37±0.84) 20 g per day 44.0 84/191) 1.07 0.76±1.52) 1.29 0.88±1.88) Smoking Non 38.3 75/196) Ex versus non) 38.0 117/308) 0.99 0.68±1.43) 0.76 0.51±1.15) Current versus non) 42.5 117/275) 1.19 0.82±1.74) 1.26 0.83±1.89) Information to doctor Yes 35.1 189/539) May be or no 49.4 121/245) 1.81 1.33±2.46) 1.55 1.11±2.16) Current Health Index 3 30.5 120/394) >3 49.6 190/383) 2.25 1.68±3.01) 2.68 1.94±3.72) Physical activity High 28.4 75/264) Low 45.1 237/525) 2.07 1.51±2.85) 1.98 1.41±2.80) Ever told hypertension No 34.2 184/538) Yes 52.0 129/248) 2.09 1.53±2.83) 1.67 1.20±2.33) Ever told diabetes No 37.6 268/713) Yes 58.4 45/77) 2.34 1.45±3.77) 1.62 0.97±2.69) History cardiovascular disease No 33.5 192/573) Yes 55.8 121/217) 2.50 1.82±3.44) 1.79 1.27±2.54) Professionally active Yes 21.9 73/334) No 52.6 240/456) 3.97 2.89±5.46) 1.55 1.03±2.34) Residence Ghent 33.0 131/397) Charleroi 46.3 182/393) 1.75 1.31±2.34) 1.79 1.30±2.44) Home Partner 39.2 260/664) Alone 42.1 53/126) 1.13 0.77±1.66) 1.18 0.77±1.80) e.g. the MONICA study 37±53%) [11], which sampled in the same cities, or the BIRNH-study 36%) [12]. We acknowledge that 38% is low, but it is the highest possible. Individuals in Belgium cannot be reached through their general practitioners, since there is no formal link between them. So we have to use the methodology as described. For legal reasons, we cannot directly contact individuals for an interview, but we have to ask for their consent. Those who did not reply to the invitation letter could not be contacted in another way. Other methods, such as mailed self-administered questionnaires, may yield a better participation 70±73%), as in a recent Dutch survey [3], but have less control on the interviewing process. The interviewers in our study were experienced nurses from relevant hospital departments urology, rehabilitation), used to deal with dif cult subjects such as sexuality. The questions about sexuality were at the end of the interview, and a relation of trust had developed between the respondent and the interviewer when arriving at this section. Although no data exist to prove

R. Mak et al. / European Urology 41 2002) 132±138 137 this, the interviewers were con dent about the quality of data they gathered. As the analysis was based on cross sectional survey results, the effects found must be interpreted as associations and not as causal relations. It was not possible to use the erectile function domain score of the IIEF to assess ED, since more than a third of the sample had no sexual activity over the last 4 weeks. In the age group 60±69 years, 47.8% had not been sexually active the last 4 weeks. Since ED and sexual activity are strongly related, those without sexual activity need to be considered when estimating the prevalence of ED in the population. All men did answer the question about con dence in getting and maintaining an erection, and this question correlated well with the extra question introduced during the study, in which men were asked to categorise themselves as having always an erection, mostly an erection, sometimes an erection or never an erection. The results of this study 10.1% severe ED, 24.7% for moderate ED) are very close to the MMAS [1], reporting 9.6% for severe, and 25.2% for moderate ED, in the age group 40±70 years. Minimal ED, however, scored higher in Belgium, but the way ED was de ned differed in both studies. Also, the relevance of minimal ED in a clinical setting is unclear. In a recent Italian study [2], the prevalence of overall ED in the age group 40±70 years was 14.0%. Again, the de nition of ED was different. It does not seem appropriate to report one rate for men between 40±70 years, when taking into account the enormous differences in prevalence of ED between the youngest and the oldest age groups. The prevalence of severe ED ranged from 1.2% in 40± 49 years group, 9.4% in the 50±59 years group to 24.5% in the 60±69 years group. For MMAS, the ranges were from 5.1 to 15%. In the Italian study, ED was prevalent in the three age groups in 4.8, 15.7 and 26.8%. In a recent Dutch study concerning men 40±79 years, the overall percentage of men answering positive to the question whether they had problems getting an erection was 13% 6% in the 40±49 years, 9% in the 50±59 years, 22% in the 60±69 years, and 38% in the 70±79 years groups) [3]. In conclusion, ED is a common disorder in Belgium, and its prevalence is comparable with what was found in other countries, although there are differences in methodology of assessment. Further analysis in this study was performed in three strata for age, the same as used for sampling. Sexual activity was most strongly related to ED. It may be easier to ask a patient whether they have recently had any sexual activity, than to immediately ask for EDs. Apart from individual circumstances, such as not having a partner, or being ill, or having an ill partner, an ED is very likely to explain sexual inactivity. The men who would have more dif culties in discussing ED with their doctor, are more likely to have ED. Finding ways to raise the subject in different ways may lower the barrier for them to discuss their sexual functioning. Obesity did not show a correlation with ED, supporting earlier studies [13]. Other conditions, such as prostate problems, hypertension, diabetes, other cardiovascular diseases, and more general complaints should make the clinician think of the possible association with ED, especially in men 60±69 years, where the background prevalence of ED is already high. As for other health conditions, leading an active life is associated with less problems with ED [13,14], as is illustrated in the results for physical activity, where in the age group 60±69 years, the OR is 2.4. It is also illustrated for professional activity, where in the age group 40±49 years, an OR of 4.4 to report ED is found for professionally inactive versus active men. Acknowledgements The authors would like to thank Ronny Pieters, Eddy De Ruyck, John Baert, Guy Vandevelde and Alfred ScarnieÁre, who did the interviews, and Christine Ghysbrechts who gave secretarial support. This study was supported by an educational grant from P zer Belgium. 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