Random sampliing helps to remove various biases that come with selection of subjects. In statistics, random sampling, is considered the best way to obtain a representative sample of a population.
You have to be 16 to get your drivers license. No younger no older
First one He hoped winning in the north would gain Europe support for the south
After a public policy has been implemented it is being evaluated. The evaluation step of public policy (last of 4, and implementation is the 3rd) checks whether the policy achieved its goal and whether it does not have unwanted side effects.