Language about evidence is often emotive. Consciously or subconsciously, writers may use language that reveals their own beliefs or hopes. This can creep into writing in many subtle ways:
The benefits of eating Vegemite sandwiches to reduce stress levels have not been studied.
The use of the positive word benefits suggests that eating Vegemite sandwiches is beneficial. The writer thinks that, when the research is in, it will confirm their belief in the benefit. But, if there have not been any studies, we do not know if it is beneficial, neutral or harmful. This is the most common sort of bias in scientific literature. Contrast it with an unbiased version:
We don’t know the effect of Vegemite sandwiches on stress levels.
Another pitfall is revealed here:
There is not enough evidence to favour red roses over white roses for those hoping for romantic success.
The use of the positive word favour influences the meaning of the sentence – because there is ‘not enough evidence’, favour red roses could just as easily be favour white roses. It is better to say:
It is not known whether sending red or white roses is more likely to help you to achieve romantic success.
Another example:
The available evidence suggests that advice to stay active has small beneficial effects for patients with acute simple low back pain, and little or no effect for patients with sciatica.
Available implies that there is ‘unavailable’ evidence that might say something different. Non-existing (or potential, possible, future, further …) evidence is just that, so do not imply that it exists and might be favourable for the issue under consideration.
