Background: Studies examining the way in which cognitive impairment is associated with depression have produced inconsistent findings. Different severity of depressed mood across studies may account for such conflicting reports. However, inconsistent results have also been reported in relation to the specific association of depression severity with cognitive performance.
Methods: A meta-analysis was conducted to examine the relationship between severity of depression and cognitive function, using the correlation (Pearson's r) between depression severity scores and neuropsychological test performance. Individual meta-analyses were conducted for composite measures of cognitive functional domains (episodic memory, executive function, processing speed, semantic memory, and visuo-spatial memory). Analyses were also done across functional domains for timed and un-timed tests.
Results: Significant correlations between depression severity and cognitive performance were found in the domains of episodic memory, executive function, and processing speed, but not for semantic memory or visuo-spatial memory. For both timed and un-timed cognitive measures there were equally significant correlations with depression severity.
Limitations: There were few studies meeting inclusion criteria in some cognitive domains, papers had to be excluded due to insufficient data reporting, and there are limitations associated with the cross-sectional design.
Conclusions: The results suggest that previous inconsistent findings of the relationship between the severity of depression and cognitive function may be attributed to random variations and lack of power within studies.