This post is largely cannibalized from something I posted on a message board, but I think it fits well here, too.
When you read about scientific studies in the newspaper, it can be hard to assess their merit. Here are a few questions to keep in mind for critical reading of science 101:
1. Where was the study published? Was it in a peer-reviewed journal, or was it just presented at a conference? (Findings presented at conferences are not subjected to peer review). In the biological sciences, journals like Science, Nature, and Cell are considered "top-tier." Medical journals, like JAMA, The Lancet, and The New England Journal of Medicine, are considered slightly more suspect, but still respectable. If you don't know the journals, it can be hard to judge, but if it sounds obscure, it probably is. One caveat to this method is that big-name people can sometimes get shitty papers into good journals on the strength of their reputations.
2. Who sponsored the study? Peer-reviewed journals require authors to disclose who financed the research, so this is easier to find out than a lot of people think. Any time a drug company publishes a study showing that its new drug cures cancer, baldness and ennui, I would reserve judgement until the results are verified by an outside party.
3. Are the results of the paper supported by other work in the field pointing in the same direction? That information is usually found in the Introduction section of the paper, where researchers discuss the foundation for the work to be presented. This is particularly important for anything you read about in the mainstream media, as they tend to have a "sensationalism bias" in what gets reported, i.e. if a study's results are unexpected, it's more likely to make the papers.
4. Did the authors draw the appropriate conclusions from the data presented? Does their explanation make sense? Does it account for all of their findings? Is there an alternative explanation, and if so, do they consider it in the Discussion section of the paper? Interpretation of the findings is the most subjective aspect of a scientific paper, but it's also the thing people are most likely to take away from reading it.