Sampling Methods

What is opportunity sampling?

When researchers decide to select anyone who is available or willing to take part

What is the process of opportunity sampling?

While doing their study, the researcher asks whoever is around to participate

Advantages of random sampling

Convenient. Saves time and effort, it is less costly

Disadvantages of random sampling

Unrepresentative of the target population, only from a specific area. The findings can’t be generalised. Inevitably biased bias, researcher has complete control over the selection of participants

What is random sampling?

All of the members of the target population have an equal chance of being selected

What is the process of random sampling?

A complete list of all members of the target population, all the names are assigned a number, a sample is ternate using a computer based randomiser

Another way to do random sampling

Use manual selection. Researcher puts each name on a separate piece of paper and places them into a container. Selects X slips from the container. Controlled : container should be shaken, slips of paper the same size, folded, selector draws blind

Advantages of random sampling

Potentially unbiased, researcher has no influence over who is selected. Every member of the target population has the same chance of selection

Disadvantages of random sampling

Hard to obtain a random sample, may not be possible to identify the members and some may refuse to take part. May end up with an unrepresentative sample

What is volunteer sampling?

Participants select themselves to be apart of a sample

What is the process of volunteer sampling?

Researcher may place an advert in a newspaper or noticeboard

Advantages of volunteer sampling

Requires minimal input from the researcher. Less time consuming, advertising allows access to a wide variety of participants, coud lead to more representative data

Disadvantages of volunteer sampling

Unlikely to be representative due to bias, makes generalisation of results difficult. Could get a biased sample from asking for volunteers, participants are likely to be motivated and helpful = volunteer bias

What is systematic sampling?

When every nth member of the target population is selected

What is the process of systematic sampling?

A sampling frame is made, a sampling system is nominated every nth member, researcher works through the sampling frame until the sample is complete

Advantages of systematic sampling

Avoids researcher bias, when the selection system is chosen, the researcher had no influence over who is chose. Fairly representative

Disadvantages of systematic sampling

Not truly unbiased, unless you select a number using a random method, start with this person then select every nth person. Unbiased selection doesn’t guarantee an unbiased sample

What is stratified sampling?

Reflects the proportion of people in certain subgroups (strata) within the target population

What is the process of stratified sampling?

Researcher identifies the different strata that makes up the population. The proportions needed for the sample to be representative are worked out. The participants that make up each stratum are selected using random sampling

Advantages of stratified sampling

Each subsection of the target population is proportionally represented. When representative, the results can be generalised

Disadvantages of stratified sampling

Compete representation of the target population isn’t possible. Time consuming to identify subgroups , then randomly select participants