Investigating links between diet and health – amalgamation, synthesis and decision making
The idea of aggregating together clinical studies to try to give a more comprehensive judgement about effectiveness goes back over a hundred years. The term meta-analysis was coined in the 1970s and the technique was refined by researchers working in the field of education. In an idealised situation, studies lower down in the hierarchies would generate hypotheses that are ultimately tested in high-quality placebo-controlled trials (RCTs) with perhaps a meta-analysis to give a consensus from these RCTs. Large studies with several thousand subjects are more likely to produce true results than smaller studies. Drugs have a minimum effective dose and all are toxic in excess so the selection of the dose for a drug or dietary supplement may affect the trial outcome; this probably applies to any intervention. One of the arguments against the traditional so-called narrative review is that these are very dependent on the individual reviewer’s choice of which studies to include or reject and which to emphasise.