Because they are an accessible population, undergraduate students are sometimes used in sociological research. in relation to the concept of generalizability, this tendency could represent a potential defect in research because:

Selection bias

Explanation:

Selection bias occurs because the sample that is taken is not representative of the general population.

If a sample is taken from the undergraduate students you can only generalize to undergraduate students.

Say that you want to know which is the most popular baseball team in the country and you take a sample from New York, and that give a result that 60% of the sample supports the Yankees. If you say "60% of americans support the Yankees" you will be commiting an error because your sample is not representative, and Californians may not share that result (for example).