Distinguishing transient versus stable aspects of depression in New Zealand Pacific Island children using Generalizability Theory.

Background: The distinction between temporary versus enduring or state/trait aspects of depression is important. More precise distinction would improve understanding of the aetiology of depression and those aspects most amenable to intervention thus identifying more homogeneous, dynamic targets for clinical trials. Generalizability Theory has been proposed as useful for disentangling state and trait components of psychopathology.

Methods: We applied Generalizability Theory to determine the relative contributions of temporary and enduring aspects of depression in a widely used screening measure of depression the - 10-item Children's Depression Inventory (CDI-10; Kovacs, 1985). Participants were children of Pacific Island descent living in New Zealand (n = 668). Data were collected at ages - 9, 11, and 14 years.

Results: The CDI-10 demonstrated acceptable generalizability across occasions (G = 0.79) with about one third of variance in total scores attributed to temporary and two thirds to more enduring aspects of depression. There were no other significant sources of error variance. Two items were identified as more sensitive than the remaining eight to more dynamic symptoms.

Limitations: Studies with briefer test-retest intervals are warranted. Use of this Pacific Island cohort limits generalizability of findings to other cultures and ethnicities. No data were collected on whether participants had received intervention for depression.

Conclusions: While the CDI-10 reliably measures both stable and transient aspects of depression in children, the scale does not permit clear distinction between them. We advocate application of Generalizability Theory for developing state/trait depression measures and determining which existing measures are most suitable for capturing modifiable features of depression.