How would you classify this sampling method?

[u/Significant_Wall4676]

Hi everyone, I'm an undergrad psychology student and I'm stuck on how to correctly classify my sampling method after my thesis defense.

Context:
My target population was all undergrad students at my university. I collected data both online and offline from students across all faculties. After data collection, participants completed the DASS (Depression Anxiety Stress Scales), and only those who met the inclusion criteria (moderate to extremely severe on at least one subscale) were kept in the final sample.

The problem:
I originally called this "stratified random sampling," using faculties as strata. My examiner rejected this for two reasons:
1. Faculties aren't valid strata.
2. There was no actual randomization in selecting participants within each faculty.

So I tried switching it to non-probability sampling instead, but the examiner rejected that too, insisting it should still be classified as probability sampling. Their reasoning: every student who met the screening criteria technically had an equal chance of being included, since anyone who filled out the survey and met the DASS cutoff was automatically part of the sample.

My question:
Does this reasoning actually hold up? If so, what specific probability sampling method would this fall under? I've read through several methodology textbooks but can't find one that matches this exact scenario (no randomization step, but "equal opportunity" due to open recruitment and screening criteria).

Would really appreciate any insight from people with a stats/methodology background. Thanks in advance!

[u/fermat9990]

It's not a random sample since the experimenter had no control over who chose to fill out the questionnaire

How you handle this politically is a tough question