shows the characteristics of the 664 patients. The sample varied by age and was predominantly White. With the exception of race, sex, marital status and melancholia, older patients differed from younger patients on all characteristics. Older patients had on average fewer lifetime depression spells and later age of onset and a higher proportion that had ever received ECT. A lower proportion of older patients had a comorbid diagnosis of generalized anxiety and older patients had more MMSE errors. Older adults also had more mobility limitations and more health conditions, but had higher levels of subjective social support and had experienced on average fewer life events the past year. The mean CES-D score was significantly lower for older patients. The patients had on average 7.8 DIS symptoms. The number of current DIS symptoms did not differ by age.
Sample characteristics at enrollment by age group (n=664)
shows the mean score for each CES-D symptom. Ten of the twenty symptoms had mean scores above 2.0, suggesting frequency and some level of severity as expected for patients with major depression. The interpersonal symptoms, people were unfriendly and people disliked me, were the symptoms with the lowest mean scores. Older patients had lower mean scores for bothered by things, thought life had been a failure, felt fearful, felt people were unfriendly, crying spells, felt sad, and felt others disliked them and had higher mean scores for poor appetite. Older patients were less likely to report enjoying life and feeling as good as others.
Mean CES-D item scores by age group at study enrollment (n=664)
shows the proportion endorsing each of the DIS symptoms. The most frequently reported symptoms were feeling sad, insomnia and having trouble concentrating. The symptoms reported the least often were attempting suicide, sleeping too much and gaining weight. Older patients were less likely to report gaining weight, feeling worthless, sinful or guilty, wanting to die and thinking about committing suicide. Older patients were more likely to endorse losing appetite, losing weight and losing interest in sex.
Percent reporting DIS symptom within two weeks prior to the interview by age group at enrollment (n=664)
With the CES-D items as indicators, a three-cluster model best fit the data. Patients in Cluster 1 (48.5%) had the highest mean scores for all symptoms compared to the other two clusters, while those in Cluster 3 (15.7%) had the lowest mean symptom scores. The symptom profiles for the CES-D are shown in . These clusters appear to differ primarily by severity.
Latent class symptom profiles based on endorsement of CES-D and DIS symptoms (n=664)
With the DIS symptoms, a three-cluster model also best fit the data. As shown in , the symptom profiles appear to show more heterogeneity than those observed in the CES-D. Patients in clusters did not appear to differ in their endorsement of weight gain, sleeping too much and moving all the time. For the other symptoms, patients in Cluster 2 (31.9%) generally had lower mean symptom scores on average compared to those in Cluster 1 (42.2%) and Cluster 3 (25.9%). Patients in Clusters 1 and 3 had similar mean scores for the symptoms with the exception of thinking a lot about death, wanting to die, and thinking about committing suicide. That is, the presence of suicidal thoughts appeared to differentiate Cluster 3 from Cluster 1.
In , we show the distribution of the sample characteristics by assigned cluster for the CES-D and the DIS. For both instruments, we observed differences by age, number of lifetime depression spells, comorbid diagnosis of generalized anxiety, and subjective social support. We observed differences across clusters identified through the CES-D but not the DIS by race and lifetime receipt of ECT. The clusters identified through the DIS differed by marital status and age of onset in addition to those in common with the CES-D.
Distribution of sample characteristics by cluster (n=664)
presents the results of the multinomial logistic regression models. We first estimated models with demographic variables only. For the CES-D and DIS cluster models, age was a significant predictor of cluster membership when other demographic, health and social variables were controlled. For both measures, comorbid anxiety diagnosis and subjective social support differentiated the clusters and were the most significant predictors of cluster membership. For the CES-D, lifetime receipt of ECT differed across clusters, as did race and the presence of melancholic depression. The DIS derived clusters were differentiated by marital status in addition to anxiety and social support.
Odds ratios from multinomial logistic regression models predicting cluster membership (n=664)
It is important to note that patients were assigned to the cluster where they had the highest probability of membership. The separation of clusters appears to be sound for both measures. For the clusters defined from the CES-D, the average probability of membership for Cluster 1 was 0.96 (range 0.51-0.99), for Cluster 2 was 0.92 (range 0.51-0.99) and for Cluster 3 was 0.94 (range 0.52-1.00). For the DIS defined clusters the average probability of membership for Cluster 1 was 0.92 (range 0.51-0.99), for Cluster 2 was 0.94 (range 0.50-0.99) and for Cluster 3 was 0.97 (range 0.58-0.99).