Research Methods RE: Sampling

Sampling
Once you have decided who you want to study this would be your target population.
It would be hard to test an entire population so you need to find a representative sample.

If the sample is not representative then it is considered biased.

Random Sampling
Everyone in the population has an equal chance of being selected.
To do this everyone in the target must be identified and you draw the names at random e.g. out of a hat or using a computer.
This is considered to be representative and have higher population validity.

Opportunity Sample
A sample that consists of those people available to the researcher.
The researcher asks people to take part and anybody who agrees or is available takes part.
There is a high chance that the population will be biased.

Volunteer Sampling
This is a sample of participants that self select by volunteering to take part in the study.
The researcher would advertise their research and people who respond would be the sample.
High chance of bias, as the people who decide to take part are a particular type
e.g. a study on gardening may attract more gardeners.