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.
Since there are several different types of purposive sampling (e.g. homogenous sampling, expert sampling, critical case sampling, etc.), one of the key benefits of this sampling method is the ability to gather large amounts of information by using a range of different techniques.his being the case, purposive sampling is useful to a researcher because they can use the variety of methods available to build and increase their research data. For example, you could start with critical case sampling, and then using the information gathered, progress to expert sampling in stage two.