Observational studies like this could conceivably be useful under different circumstances. I think the chances of distinguishing meaningful from meaningless cor

Observational studies like this could conceivably be useful under different circumstances. I think the chances of distinguishing meaningful from meaningless correlations would probably be higher if the variable being studied wasn't as ubiquitous as eating nuts and the causes of death weren't ordinary diseases of aging. For instance, an observational study could help determine the risk of disease from living in a specific area that was contaminated with a specific toxic substance. In order to make a very convincing case that the toxin had caused the diseases, you'd want to support it with stronger kinds of studies, that, say, demonstrated that that chemical was capable of causing the diseases that were observed. nuts do seem to have some desirable nutritional properties (high on unsaturated fats, protein and minerals) The problem is that none of those other components of food have been shown to prevent death, either, except in weak studies like this one. It's all very circular.