You should not generalise statistically beyond your sampling frame.

Mixed sampling is to use a combination of two or more discrete samples, each selected using either probability or non-probability procedures.

Your sample will need to be larger to ensure sufficient responses for the margin of error you require.

If your research question or objective is concerned with members of a student society, your sampling frame will be the complete membership list for that society.

Convenience sampling involves selecting haphazardly those cases that are easiest to obtain for your sample.

Whatever your research question, an understanding of techniques for selecting samples is likely to be very important.

Non-probability sampling is often associated with survey and experiment research strategies.

The majority of non-probability sampling procedures include an element of subjective judgement.

Choice of sampling techniques depends upon the research objectives.

you will be drawing conclusions from these analyses about the target population from which your sample was not selected.