Answer:
cross-sectional
Explanation:
cross-sectional research method -
It is the type of observation which analyze the data from the population for a specific period of time , is referred to as cross-sectional research method .
In the medical research , they are used to some feature of the population , such as the prevalence of any disease , age related changes for young and old peoples .
Hence , according to the question , the best research method is the cross-sectional research method .
