Psychological Medicine, 1997, 27, 875–883. Copyright # 1997 Cambridge University Press Fifteen years on : evolving ideas in researching sex differences in depression K. WILHELM," G. PARKER  D. HADZI-PAVLOVIC From the Mood Disorders Unit, Prince Henry Hospital, Sydney, NSW, Australia. ABSTRACT Background. A cohort study of a socially homogeneous group of teachers was commenced in 1978 to pursue possible risk factors contributing to the recognized female preponderance of depression. Methods. Multiple measures of depressive experience included : (i) lifetime rates, duration and number of depressive episodes using two caseness definitions, DSM-III-R major depression and ‘ all depression ’ (which included a category of minor depression) ; (ii) self-report measures of state and trait depression, neuroticism, and self-esteem. DSM-III-R anxiety disorder rates are also reported and co-morbidity with major depression examined. Results. At the 15-year review in 1993, the sample had a mean age of 39 years, there was a trend for a female preponderance in lifetime rates of major depression and ‘ all depression ’ (and which was more pronounced with the inclusion of data for anxiety disorders), with statistically significant differences in rates of social and simple phobias and combined anxiety disorders. Mean neuroticism scores were consistently higher for women. Conclusions. The strong association between anxiety and depressive disorders suggests that greater reporting of anxiety and higher neuroticism scores in women may be a key determinant that con- tributes to any female preponderance in depression rates. INTRODUCTION Depression is a common disorder with significant impact in terms of symptoms and disabilities, and with substantial social and economic costs. Since Weissman & Klerman’s comprehensive review (1977) of gender differences in depression, there has been a continuing interest in depression rates between the sexes, since similarities as well as differences can provide insights into risk factors to both the development and continu- ation of depressive episodes. In 1978, we commenced a longitudinal study of a socially homogeneous group where a number of potential psychosocial risk factors (such as education and job opportunities) were similar for both sexes, anticipating comparable depressive experience for men and women as equivalent depression levels are generally re- ported in college and university samples (Jorm, " Address for correspondence : Professor K. Wilhelm, Caritas Centre, 299 Forbes Street, Darlinghurst, Sydney, NSW 2010, Australia. 1987). In following that young adult cohort (whose mean age at baseline was 23 years) over time, we anticipated the subsequent appearance of a female preponderance in depression rates and, by having baseline and prospective data, we hoped to identify likely determinants. Depressive experience is not a single construct and may be measured in a number of ways. For example, one may be interested in the subjective experience of depressive symptoms rated in terms of ‘ caseness ’ (a categorical state) or severity (a dimensional concept). Again, measures may assess patient or non-patient status (a categorical state), or assess functioning (a dimensional rating). We examine various methods of defining depression to consider whether sex differences are more evident across some constructs than others. Lifetime case rates using two different symptom thresholds are reported in this account of our 15-year review : major depression (where subjects reported 5}9 or more symptoms from DSM-III-R criteria) and minor depression (using the criteria of 875