No single study can be considered to be strong evidence – it is merely indicative.
Some claims are based on only one study. Even when the study involved a fair comparison, no single study can be considered to be strong evidence – it is merely indicative.
Single studies of the same intervention can have very different results. This can happen because they were small studies with few people, the organizations and/or the populations in which the intervention took place were different, or because different measurement methods were used.
Claims that are trustworthy are often supported by meta-analyses or systematic reviews – a type of study in which statistical techniques are used to combine the results of single studies in order to achieve a more accurate estimate of the effect.
Claims based on a single study are not trustworthy