The most important aspect of a probability sample is that it represents the target population.

Bias resulting from respondents similar in meaningful ways from non-respondents is known as non-response bias.

It is important to ensure that your sampling frame is valid.

Mixed sampling is to use a combination of one discrete sample, using either probability or non-probability procedures.

Even after ineligible and unreachable respondents have been included, it is probable that you will still have some non-responses.

Probability sampling can be used generalise statistically about a target population.

When a sampling frame is not possible probability sampling is used.

Probability samples where you do not have a sampling frame.

Samples of larger absolute size are more likely to be representative of the target population from which they are drawn than smaller samples.

For all research questions where it would be impracticable for you to collect data from the entire population by interviews, you need to select a sample.