And how would you define evidence, would that only be scientific evidence, or would you include personal experience ?
The problem with personal experience is just that - it is personal, and unique, it often does not represent the "full picture".
Scientific evidence is more robust usually as it has a larger number of cases and therefore more likely to be valid in a decision making process.
You can of course use personal experience as evidence if it is formally assessed in a controlled and systematic way
For instance:
Take a bike and paint it pink. Then try and sell it ...
The first random customer is a boy
The personal experience is that you cannot sell a pink bike.
If the first random customer is a girl then the personal experience is that pink bikes are easy to sell
However if you tried selling it to two random children the personal experience would be totally different - the outcome is more valid as you now know you can sell pink bikes to girls, but not to boys.
Of course the girl may be a tom boy and the personal experience is that you cannot sell pink bikes to either girls or boys.
Now take a hundred random children and personal experience is nearer the truth - that you can sell pink bikes to girls, but not boys
The case of facial injury is a prime example. The statement was that the personal experience was that a helmet is wide enough to protect from facial injuries so a full face helmet was not needed.
The combined personal experiences of a cohort of cyclist showed that this is clearly not the case.