Engaging with the existing literature would be a good start. If you were interested in studying the relationship between bias and funding you might do a survey

Engaging with the existing literature would be a good start. If you were interested in studying the relationship between bias and funding you might do a survey of published papers and articles on the subject. If you can identify some measurable criteria that can be used to rate how "green" a paper's funding is then you can use that as an axis and compare the surveyed papers to reveal trends.