I want to perform a meta-analysis but the included studies use different models to analyze the data. There are Pearson correlation (3 studies), Spearman correlation (1 study) and several studies (~7-10) with regression coefficients (linear regression, weighted least squares regression, multivariate regression, and so on).
What would be preferable (and possible): a) to use the correlation coefficients. In this case should I ask for data to authors of the remaining articles that didn't use correlation and calculate it, or is there any way of extracting it from the beta coefficient? b) perform a meta-analysis of beta coefficients. Is this possible? How can I analyze such different models?
What can you suggest me?