This paper summarizes how the partisan influence literature assesses the relationship between the left-right party composition of government and policy outputs through a meta-analysis of 693 parameter estimates of the party-policy relationship published in 43 empirical studies. Based on a simplified `combined tests' meta-analytic technique, we show that the average correlation between the party composition of government and policy outputs is not significantly different from zero. A mutivariate logistic regression analysis examines how support for partisan theory is affected by a subset of mediating factors that can be applied to all the estimates under review. The analysis demonstrates that there are clearly identifiable conditions under which the probability of support for partisan theory can be substantially increased. We conclude that further research is needed on institutional and socio-economic determinants of public policy.