In general, target population is another name for survey population.
In quantitative research, sample units are chosen in a systematic manner and are easily identifiable and clearly defined; in qualitative research they are not.
In probability sampling, every unit of the target population has an equal, calculable and non zero probability of being included in the sample.
A sampling procedure including a sequence of samples, each drawn from one previously selected for this purpose, and where only the last sample is studied, is called multi-phase sampling procedure.
A multi-stage sampling that takes samples from within geographical areas (for example, states, regions, cities, streets, and so on), and where the final sample is fully studied is called spatial sampling.
A trend study is a longitudinal procedure which studies different people at different times, using the same methods and instruments.
A study is said to have reached a point of saturation when studying additional respondents does not produce any new information.
Qualitative researchers are more likely to employ non-probability sampling procedures than quantitative researchers.
In snowball sampling respondents are chosen continuously during the research process, after parts of data have been collected.
The more homogeneous the target population, the more likely it is that a large sample will be required.
In multi-stage sampling, a series of samples are drawn from the same original sample. Each sample is studied adequately, before further samples are drawn.
Quantitative researchers employ sampling procedures, qualitative researchers do not.