Sampling techniques

IB Psychology· Research methodology· 11 min read

1. Core concept

A sampling technique is the method used to select participants from a target population, and each has trade-offs. Random sampling gives every member an equal chance and reduces bias but is hard to achieve; opportunity (convenience) sampling is quick but often unrepresentative; volunteer (self-selected) sampling is easy but attracts a particular kind of person; stratified sampling divides the population into subgroups and samples each in proportion, improving representativeness; snowball sampling reaches hard-to-find groups through participant referrals at the cost of representativeness. The technique affects how far findings can be generalized, because it determines who ends up in the sample.

2. Key studies

IB Psychology answers must be supported by named studies. Learn these to cite as evidence:

📘 Definition

Chang et al. (2023)

In a sample of Chinese college students, trait mindfulness was negatively associated with social-media addiction, partly via attention control and reduced FOMO. — A convenience/volunteer sample of students — fast to recruit, but its narrowness (one age group, one country, self-selected) is exactly the sampling limit that bounds generalization.

3. Evaluation (AO3)

Strength — controls a key source of bias — Choosing an appropriate technique — ideally random — reduces sampling bias and strengthens the case for generalization.

Limitation — practicality wins in reality — True random sampling is rarely feasible, so most psychology relies on convenience or volunteer samples, building in a bias that must be acknowledged.

4. Scope

5. Common Pitfalls

Wrong move:

Describing the sample (who took part) is the same as describing the sampling method (how they were chosen).

Why:

A frequently penalised misconception in IB Psychology exams.

Correct move:

The sampling METHOD is the selection procedure — self-selected (volunteer), opportunity, stratified, random, snowball — with its characteristics; listing participants' age or number describes the SAMPLE, not the technique. Name and describe the procedure.

Going deeper

Generalizing findingsthe sample's representativeness drives generalizability (RM_7).
Reflexivitysampling bias is distinct from the researcher bias reflexivity targets (RM_8).