We have quite a lot of questions tagged reference-request; with 92 questions at the time of writing, it's one of our most popular tags. However, not every study that is cited in an answer to such questions is equally valid.
Wikipedia introduces the concept of validity as follows:
Validity of an assessment is the degree to which it measures what it is supposed to measure.
It is to be distinguished from reliability (continuing from the previous quote):
This is not the same as reliability, which is the extent to which a measurement gives results that are very consistent. Within validity, the measurement does not always have to be similar, as it does in reliability. However, just because a measure is reliable, it is not necessarily valid. E.g. a scale that is 5 pounds off is reliable but not valid.
Since we have so many questions that ask for answers backed up by studies, I would like to know if questions asking about the validity of a specific study on language learning or teaching would also be on topic here.