ABSTRACT

This PhD dissertation is based on four scientific papers. The research was carried out at Psychiatric Research Unit, Frederiksborg General Hospital in Hilleroed.

The studies include a validation of the Major Depression Inventory (MDI), a scale fulfilling the ICD-10 as well as DSM-IV depression criteria. The validation study included 91 persons suffering from depression in various degrees. The main investigation was performed in the general population: 2000 Danish residents were randomly selected, the sample including an equal amount of men and women in the age range 20 to 80 years. Questionnaire booklets including the MDI, the SCL-92 (to measure mental distress) and a number of bio-psycho-social variables were mailed to the sample population.

The results showed that the MDI is a useful self-rating depression scale, tested amongst others by IRT. The MDI can be used for the diagnosis and measurement of the severity of depression. The prevalence of depression in the Danish general population was found to be 4.1%. Norms for gender and age were estimated. The well-known gender difference of twice as many women as men suffering from depression was not replicated, especially not among the most severely depressed respondents. At the time of the investigation, only 13% of those suffering from depression were treated by a medical doctor for a nervous disorder. None of these were male. Traumatic events in the family during the last year as well as overconsumption of alcohol were seen to be associated to the prevalence of depression.

The SCL-92 was tested by IRT. A scale consisting of 63 non-psychotic or neurotic items was accepted as a unidimensional scale, and the six underlying subscales were all individually accepted. Norms for gender and age were estimated. Comparisons with distress scores from other countries were performed, cut-off scores for caseness were estimated and the importance of comparing with relevant data was demonstrated. Cut-off scores for depression were estimated, using the MDI as gold standard. Traumatic events during the past year in the family or at work, a somatic disorder, and social status were all seen to have an impact on the degree of distress.

The MDI is a useful instrument for measuring prevalence and severity of depression. In the Danish general population, the prevalence of depression was in accordance with other studies, but the female:male ratio was lower than found in most studies. Many depressed are untreated, especially in the male population.

The SCL is an important instrument for measuring the degree of mental distress and has shown to be sensitive to long-term as well as to short-term variables.

Normative data have been obtained for both the MDI and the SCL, which is of great importance for future research in the area.