Models from Leidong Zhang
The sample is randomly selected and is representative of the general group
Quantity of the sample, are the respondents representative, changing scope
To point out that the current sample is not randomly selected and could not represent the general group or that the survey only special groups of subjects while many people have been ignored
The author implies that the sample studied in the survey could present the general group, but the author consider only (the selective sub-group)
Although the sub-group studied do constitute a significant part of the general group, many other sub-groups are excluded from the study.
The conditions situation of other sub-group might be quite different.
Without ruling out the above possibility, the author could not make any general conclusion about that the general population (do something) merely based on the selective sub-group.