How can I tell whether a sample was selected randomly or just happened to be easy to reach?

Start with the selection process, not the survey’s size or the word “random” in its description. Ask: Who was eligible, how were people chosen, and could someone explain the chance-based selection rule? A random method gives population members an equal chance of selection. For example, if the target group is all members of one club, selecting names by chance from a complete list of those members is a random approach. Asking the members who happened to be in the room after school is convenience sampling. [S1]

The key clue is whether selection depended on being available or easy to reach. A large group of nearby respondents does not, just by being large, show that members who were absent or harder to reach had a chance to be included.

Ask for a plain-language account of the steps. For instance: Was the roster the full list of the group they wanted to describe? Were names chosen by chance from that list, or did someone choose names they recognized, could contact quickly, or expected would answer? A complete list followed by chance-based selection supports describing the method as random; choosing whoever was easy to reach supports calling it convenience sampling. [S1]

You don’t need to demand technical jargon. A useful explanation names the eligible group, the list or source used to find people, and the rule for choosing them. If those details are missing, say that the method is unclear rather than guessing. Also distinguish selection from response: ask whether the description explains who was invited or who actually answered. If the account only describes answers collected from people already present, that is a clear sign of convenience sampling.

Be cautious. If the survey was offered to whoever happened to attend, it is a convenience sample: access depended on being at that meeting. The answers describe the respondents, but the selection method alone does not establish that they represent every club member. Convenience samples may be biased, and conclusions about a wider group depend on how the sample was collected. [S1]

For example, suppose the attendees who answered prefer Tuesday. You can report, “Among the members who answered at this meeting, Tuesday was the preferred choice.” Don’t turn that into “The club prefers Tuesday” unless you have a sound basis for applying the result to all members. This example is hypothetical; no actual survey results are being asserted. If the organizer wants to describe all club members, ask how absent members were included or whether names were selected by chance from a complete club list. Even a chance-based selection describes its defined group; it does not automatically say what students outside that group prefer.

Use this fill-in template:

“Target group: [who the survey aims to describe]. People were selected by [specific steps]. This is [random sampling / convenience sampling / unclear] because [reason tied to the selection process]. The responses describe [who actually responded]. They do not, by themselves, establish what [broader group] thinks.”

Example, assuming the survey was offered only to students present at a club meeting: “Target group: all members of the [Club]. The survey was offered to whoever attended the [meeting]. This is convenience sampling because availability at that meeting determined who could take part. The responses describe the members who answered; they do not, by themselves, establish what all club members prefer.” Keep the group and the wording as placeholders unless you know the actual details. The label should follow the process you can describe, not the conclusion someone hopes to make. [S1]