Site selection cannot be convenience because usually generalization wanted, and purposive sample can be typical and representative of diversity and best and worst cases; number of cases depends on program diversity since generalization usually wanted; data rely on common instruments, published documents, and observation; reports are varied in theme, site, chronology, and narration
Sites should not be selected based on convenience.
There are no best and worst cases.
A man is sleeping.
Most detergents work well in cold water.
Women are selling things.
The children on the boat are blindfolded and can't see the yellow floor.
They must have really hurt these monsters.
It was by chance that the alpha males left.