Misleading description

Few people or events

Look out for effects of nutrition interventions that are based on small studies with few people.

Sometimes, in studies on the effects of nutrition interventions, only a few people were included (“small studies”), or there were few events. The results of studies like these are sometimes described as though we can be sure about the results. However, in such studies, it is likely that effects occur purely by chance, rather than as a consequence of the nutrition intervention. Thus, what seems to be real effects, may well have just occurred by chance.

In other words, some people would have got better or worse anyway, regardless of the nutrition intervention they received. And it is possible that there just happened to be more of those people in one group than the other.

The fewer people included in a study, or the fewer the events, the bigger the risk of results occurring purely by chance. It is like tossing coins. The chance of getting “heads” when you flip the coin is 50%, as is the chance of getting “tails”. But if you flip the coin just 10 times, you may get 8 “heads” and 2 “tails”, or any other combination, but you are unlikely to get exactly 5 “heads” and 5 “tails”. If you increase the number of times you flip the coin, for example, 1000 times, you will end up being closer to getting 500 “heads” and 500 “tails”.

REMEMBER: You can’t be sure about the effects of nutrition intervention that are based on small studies with few people or few events.