Question: is this a 2) strong advice, 1) weak advice 0) no advice?

We suggest that, if possible, attempts to investigate additional phenotypes that may be associated with a variant should not use individuals that have been ascertained on the basis of the phenotype of interest; instead, they should be drawn from independent cohorts and selected solely on the basis of being a carrier of the variant under study. 
user
This is no advice
assistant