Only responders who had answered all questions relevant to the analyses were included. We calculated the prevalence of adverse social factors and compared frequent attenders and infrequent attenders by calculating the prevalence difference and the prevalence ratio. The prevalence ratio was preferred to the odds ratio because the prevalences of the social factors were high (>20%); the odds ratio thus overestimated the associations.23,24 For each social factor, the prevalence difference between frequent and infrequent attenders was calculated using a binomial generalised linear model with identity link, and the prevalence ratio was calculated using a binomial generalised linear model with log link.
How this fits in
Social inequality in health is well-documented. The social conditions of frequent attenders in general practice are poorer than those of other patients. As for men, social conditions may in themselves determine frequent use of general practice after adjustment for social inequalities in health. The likelihood of female frequent attendance tends to increase with adverse social conditions. GPs should be aware of the role social factors may play as reasons for encounter and should try to show patients ways to improve their social conditions in order to prevent inappropriate attendance and iatrogenic illness.
To adjust the prevalence ratio for the patients' health status, each social factor was adjusted by means of scores on ‘Physical Functioning’ and ‘Mental Health’ and the Whiteley-7 index (that is, only a single social factor was included in each regression model). ‘Physical Functioning’ and ‘Mental Health’ scores were divided into quartiles based on data of the general Danish population. The Whiteley index was dichotomised with a cut-off between 0 and 1. The adjusted prevalence ratio of a social factor was calculated using Poisson regression25 with robust error estimate. Robust error estimate was used to correct for variance overestimation when applying Poisson regression to binary data.26 The analyses were performed separately for women and men, but for all age strata collectively, adjusting for sampling probabilities within each age stratum.24,27 To prevent incorrect claims of statistical significance due to multiple tests, the significance level was lowered according to the Bonferroni method (α divided by the number of outcome measures). Therefore, probabilities of ≤0.006 were regarded as statistically significant. STATA 8.0 was used for the analyses.