sampling

Random Sampling how

Obtain a complete list of all members of the target population.

Random Sampling how

select a random person using a computer-based randomiser

Random Sampling advantage

• Reduces investigator bias in sample selection.

Random Sampling advantage

• Use of chance makes the sample more likely to be representative of the target population than other methods.

Random Sampling disadvantage

• Time-consuming to gain a complete list of everyone in the target population.

Random Sampling Disadvantage

• Time-consuming to gain a complete list of everyone in the target population.

Systematic Sampling

Produced through time list

Systematic Sampling how

A sampling frame is produced (a list of people in the target population)

Systematic Sampling

The list is organised, e.g. alphabetically.

Systematic Sampling

Reduces investigator bias, especially if the system is randomly chosen.

Systematic Sampling

Relatively representative, e.g. unlikely to get an all-male sample.

Systematic Sampling

Less representative than other methods

Systematic Sampling

Time-consuming, and selected participants may not want to take part.

Stratified Sampling

Identify sub-groups (strata) within the population

Stratified Sampling

Work out proportions needed to make the sample representative.

Stratified Sampling

Most representative method because the population is targeted around sub-groups

Stratified Sampling

Avoids investigator bias.

Stratified Sampling

Identified strata may not reflect all differences between people, so it is not 100% representative.

Stratified Sampling

Time-consuming compared to other methods.

Opportunity Sampling

Select subjects who appear suitable, willing, and available at the time.

Opportunity Sampling

Ask them to take part until enough participants agree.

Opportunity Sampling

Quickest and easiest method.

Opportunity Sampling

Useful for researchers with fewer resources (e.g. students).

Opportunity Sampling

• Sample bias (often only from one area

Opportunity Sampling

Researcher bias in who is selected.

Opportunity Sampling

Some people may refuse to take part.

Volunteer Sampling

The researcher places an advert (e.g. newspaper or notice board).

Volunteer Sampling

The advert stays up until enough participants agree.

Volunteer Sampling

Minimal time and effort from the researcher.

Volunteer Sampling

Avoids investigator bias

Volunteer Sampling

Unrepresentative due to volunteer bias.

Volunteer sampling

Participants are often more helpful, keen, or curious, so they may perform better.