Most meta-analysts in different fields would typically run both models, but prefer placing emphasis on random effects. For many GWA studies, however, only fixed effects are reported. Statistically significant associations in fixed or random effects calculations certainly need further documentation and replication. Random effects may sometimes yield spuriously large summary effects when selection biases operate differently in small versus larger studies. If a meta-analysis of GWA studies can ensure that there are no such biases within its confines (e.g. including all data from a well-circumscribed consortium), then this is no longer an issue. Conversely, when small studies have smaller effects than larger studies and results are heterogeneous, random effects calculations may give stronger overall statistical significance for the summary effect.
