How do you combine probability to non probability sampling?

Answer 1

There are many methods: stratified random sampling and cluster sampling are two examples.

Suppose you have a school with 1000 pupil: 400 in the Junior school and 600 in the Senior school. You may wish to keep the sampling proportions in the two parts of the school the same. So if you wanted a sample of 5% = 50 pupils, you would take a probability or random sample of 5% = 20 from the Juniors and 5% = 30 from the Seniors.

For the second example, imagine you want to sample 5% of all schools in the country. This could result in you spending lots of time and money travelling from place to place. Instead, you divide up the country into 100 regions - each containing the same number of schools. You then take a probability sample of 5% of these regions. In each of the regions you visit every school.