Choice-based sampling is one of the stratified sampling strategies. In choice-based sampling,  the data are stratified on the target and a sample is taken from each stratum so that the rare target class will be more represented in the sample. The model is then built on this biased sample . The effects of the input variables on the target are often estimated with more precision with the choice-based sample even when a smaller overall sample size is taken, compared to a random sample. The results usually must be adjusted to correct for the oversampling.
The sampling strategy that you select in your dissertation should naturally flow from your chosen research design and research methods , as well as taking into account issues of research ethics . To set the sampling strategy that you will use in your dissertation, you need to follow three steps: (a) understand the key terms and basic principles ; (b) determine which sampling technique you will use to select the units that will make up your sample; and (c) consider the practicalities of choosing such a sampling strategy for your dissertation (., what time you have available, what access you have, etc.).