1 a variable other than the explanatory variable considered that could be partly responsible for the relationship observed. 4 a trend that appears in different groups of data but reverses when these groups are combined disappears or. 6 to choose a sample representative of the population. 8 population ge employees sampling frame entry level employees sample selected 150 employees. 10 simple random sampling everyone in the populationhas an equal chance of getting selected. Ex out of the whole population pick a few randomly stratified sampling divide the population in groups and then randomly choose. Ex divide population in groups and pick a few fromevery a few from each group group cluster sampling divide a population in large clusters and pick a few selected clusters. Multistage sampling combo of two or more methods. 11 convenience sampling selects whichever units of the to reach population are easiest.