Methodology : Selection of Participants

Identification of Sample and Population

Population

• The entire group of interest to the research

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Sample

• A subset of the population

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Example

• A researcher is interested in studying the effects of a new medication on people with a particular medical condition. They recruit 100 participants aged between 18-40 who have the medical condition.

  • Population: all people who have that medical condition

  • Sample: the 100 people aged 18-40 with the medical condition

Convenience Sampling

Application

• Many studies use university students as this is where studies are conducted

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Method

• Convenience sampling is a sampling technique that involves selecting individuals who are easily accessible or available to participate in the study.

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Strengths

• Relatively quick and therefore inexpensive

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Limitations

• Higher potential for bias

• Lack of generalisability

Snowballing

Application

• Often used when population of interest is difficult to access or hidden

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Method

• Involves recruiting participants through referrals from other participants.

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Strengths

• Access hard-to-reach populations

• Cost-effective

• Potential for a diverse sample

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Weaknesses

• Higher potential for bias

• Limited generalisability

Random Sampling

Application

• Used so that every member of the population has an equal chance of being selected. Ideal method for many studies (but difficult to achieve).

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Method

• Involves selecting individuals or objects from the population at random

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Strengths

• Representative sample

• Reduced bias

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Limitations

• Relatively cost-and time-intensive

• Difficult to truly achieve

Stratified Sampling

Application

• Used when wanting to ensure categories are represented

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Method

• Stratified sampling is a sampling technique that involves dividing the population into subgroups, or strata's, based on certain characteristics, such as age or gender.

• A random sample is then selected from each stratum. 

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Strengths

• Representative sample

• Increased efficiency

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Limitations

• Need for prior knowledge

• Time-and cost-intensive

Allocation of Participants

Random Allocation

Application

• Random allocation is commonly used in experimental research, where participants are randomly assigned to either a treatment group or a control group.

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• Used to control for individual differences between participants and to ensure that the treatment and control groups are equivalent before the treatment is administered.

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• Can also be used in non-experimental research to assign participants to different conditions or groups, such as in observational studies.

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Method

• Assign participants to different groups using a random process (e.g. using a computer program, a random number table)

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• The key is that each participant has an equal chance of being assigned to any group, and the process is completely random.

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Strengths

• Reduced bias

• Increased internal validity

• Enhanced generalisability

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Limitations

• Greater potential for confounding variables

• May not be practical for all studies