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.
The same sampling fraction is used for each stratum regardless of the differences in population size of the strata. Disproportionate Stratified Random Sample. In disproportionate stratified random sampling, the different strata do not have the same sampling fractions as each other.roportionate Stratified Random Sample. In proportional stratified random sampling, the size of each strata is proportionate to the population size of the strata when looked at across the entire population. This means that each stratum has the same sampling fraction.