Results when Googling "problem-solving therapy meta-analysis" (as of Nov 2018:

Alissa Bell (Jun 2009) Problem-solving therapy for depression: a meta-analysis. [Full Text]

• Ph.D. in clinical psychology at Stony Brook University (Long Island)
• Two authors to study
• Involved 21 independent studies
• Showed significantly more effective than controls

Julia Kirkham (May 2016) Meta-analysis of problem solving therapy for the treatment of major depressive disorder in older adults.

• Psychiatrist and fellow at Division of Geriatric Psychiatry at Queen's University in Kingston, Ontario
• Significant (6.94) effect size for alleviating major depressive disorder symptoms