The most significant challenge is ensuring the secondary data truly fits your specific research question.
Variable Mismatch: The variables available in the data set might not perfectly align with the constructs you wish to measure. You might have to use proxy variables, which can weaken the validity of your conclusions.
Conceptual Differences: The original collectors may have defined concepts or categories differently than you would, potentially leading to misinterpretations if not carefully accounted for.
Scope and Population: The original data's geographic scope, population surveyed, or time frame might not precisely match your desired research parameters, requiring careful justification or limiting the generalizability of your findings.