Skin discoloration can be due to changes in melanin. Melanin is a skin pigment that gives color to the skin. Changes in melanin can also cause skin to be patchy.
Probability sampling, or random sampling, is a sampling technique in which the probability of getting any particular sample may be calculated.Nonprobability sampling does not meet this criterion and, as any methodological decision, should adjust to the research question that one envisages to answer.ampling is the use of a subset of the population to represent the whole population or to inform about (social) processes that are meaningful beyond the particular cases, individuals or sites studied.
Purposeful Sampling for Qualitative Data Collection and Analysis in Mixed Method Implementation Research. Purposeful sampling is widely used in qualitative research for the identification and selection of information-rich cases related to the phenomenon of interest. Although there are several different purposeful sampling strategies, criterion sampling appears to be used most commonly in implementation research. However, combining sampling strategies may be more appropriate to the aims of implementation research and more consistent with recent developments in quantitative methods.