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.
Purposive sampling. Purposive sampling, also known as judgmental, selective or subjective sampling, is a type of non-probability sampling technique.urposive sampling. Purposive sampling, also known as judgmental, selective or subjective sampling, is a type of non-probability sampling technique.