These studies are very crude. They are used to indicate areas that might bear more detailed study. That s it. Cross-sectional studies are the weakest of all epidemiological studies. Some studies aren t original research but rather a review of all previous studies on the topic.
Researchers draw on all the findings and try to reach some overall conclusion.
Meta-analyses are controversial because they attempt to draw comparisons between studies of different designs. Other science studies. Scientific research in other disciplines biology, ecology, chemistry, etc. tend to deal with testing a single hypothesis in a single, limited problem. By themselves, they aren t news. What makes them news is the context and implications of the study.