RM- sampling methods

If a sample is representative, the results can be generalised to the whole population

General population

Everyone in the world

Target population

Total group of individuals which may be picked

Why you need a sample of the target population

Not everyone will consent

Takes a long time to test everyone

5 Sampling methods

Opportunity

Volunteer

Random

Systematic

Stratified

Opportunity sampling

Sampling whoever is convenient, available and willing to take part in the study

Pro of opportunity sampling

Convenient- quick, easy and cheap

Cons of opportunity sampling

Extremely biased- might unconsciously approach people who will support your hypothesis (so is unrepresentative)

Time consuming

Volunteer sampling/ self-selection

Participants are self selecting by responding to an advert

Pros of volunteer sampling

Less time consuming than other methods

People are willing to participate- drop out/attrition rate is low

Cons of volunteer sampling

Prone to volunteer bias- lowers the validity of the study

Prone to demand characteristics

Sampling that uses random mechanisms (equal chance of being picked)

Random

Systematic

Stratified

Random sampling

Everyone in the target population has an equal chance of being selected

How to do random sampling

1) Write all the names of the target population onto separate pieces of paper and put them into a hat

2) Pick out 25 names and ask the individuals if they want to participate in the research

3) Keep doing this until 25 individuals have accepted to be apart of your study

Pro of random sampling

No researcher bias- so representative if done right

Con of random sampling

Time consuming- need the whole list of target population and you then need to ask if they want to be in your research

Systematic sampling

Having a list of the target population and picking people off it in a systematic manner

How to do systematic sampling

1) Roll a dice for a number

2) Go through the list and pick the nth name you come across

3) Repeat until you have the desired sample number

Pros of systematic sampling

Reduced researcher bias

Representative of the population

Cons of systematic sampling

Time consuming- have to wait for responses from individuals whether they want to participate

Might systematically miss certain characteristics

Stratified sampling

Dividing the target population into strata’s based on key characteristics then sampling them in proportion to the sample population

Pro of stratified sampling

Representative- findings can be generalised to the population

Con of stratified sampling

Time consuming and difficult to group people