I am conducting a secondary, quantitative study. The cohort was identified from newspaper articles and then data were gathered from public court records. The population includes all people convicted of murder in the state and the cohort includes those whose articles were located in three major newspapers in that state. Additional data were also obtained from public criminal records.
How should I define the sample? Purposeful? Criterion? Convenient?
If identifying the cohort from newspaper reports was simply a way to gather a group of murderers, then it could be argued that the sample is convenient.
If having one’s name mentioned in the newspaper is essential to belonging to the cohort (i.e., you want to evaluate the effects of being mentioned in a newspaper on a particular outcome), then it could be argued that the sampling is criterion.
I admit I am not familiar with criterion sampling, but sampling based on a specific criterion does not seem to rule out that it is also a convenience sample. It is certainly not random sampling. If I understood you correctly, it would be the analysis of the entire population if all people convicted of murder were also mentioned in the newspaper? But since cannot check this assumption, I guess, it is a sample; and it is unlikely to be a random sample because the people mentioned in the major newspaper are not systematically different from people mentioned in smaller newspapers (e.g., because the crimes differ).