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POPULATIONS, SAMPLES, AND SAMPLING TECHNIQUES

The Research Challenge

Generalizing Findings

In psychological research, the goal often extends beyond the individuals directly studied to generalize findings to a larger group or population. Understanding populations, samples, and how samples are chosen is crucial for this generalizability and the validity of research results.

Study Outline

1

Target Population & Sample

The defined group of interest versus the participants studied.
2

Sampling Techniques

Methods used to select participants (Random, Snowball, Opportunity, Self-Selected).
3

Validity and Bias

How sample size and representativeness affect conclusions.

Core Definitions

These definitions are crucial for ensuring findings can be applied beyond the participants studied.

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Target Population

Target Population refers to the entire group of people the researcher wants to learn about. For example, "all adults aged 18-35 in the UK" might be a target population.
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Sample

Sample is the smaller group of participants actually studied. This group is selected to represent the target population and enables researchers to make inferences about the population as a whole.

Random Sampling

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Strengths It minimizes bias and increases the representativeness of the sample, enabling legitimate generalization.
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Weaknesses It can be difficult and time-consuming to access an entire population list, and may not be practical for very large populations.

Snowball Sampling

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Strengths Useful when the target population is small or hard to identify.
❌
Weaknesses Sample can be biased and unrepresentative because it relies on social networks.

Opportunity Sampling

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Strengths Quick and easy, cost-effective.
❌
Weaknesses Likely to be biased due to lack of randomness and representativeness, limiting generalizability.

Self-Selected Sampling

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Strengths Easy to collect participants, especially for online or large-scale studies.
❌
Weaknesses Biased because people who volunteer may differ systematically from non-volunteers in ways relevant to the study (e.g., more motivated or interested).

Validity Check

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The Representativeness Rule: Sample size affects the power of the research—the ability to detect real effects. Larger samples reduce random errors and increase confidence. Sampling bias occurs when samples systematically differ from the population, reducing the validity of conclusions. Proper planning and justification of sampling methods are vital, as poor sampling undermines the research's scientific credibility.

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Sampling in Psychological Research
Term
Target Population

What is a target population in psychological research?

Answer
Definition

The entire group of people the researcher wants to learn about.

Term
Sample

What is a sample in psychological research?

Answer
Definition

A smaller group of participants selected to represent the target population.

Term
Representativeness

Why is representativeness important in sampling?

Answer
Importance

It ensures the sample accurately reflects the target population, allowing generalization of results.

Term
Random Sampling

What is random sampling?

Answer
Definition

A sampling method where every member of the target population has an equal chance of selection.

Term
Strength of Random Sampling

Name a strength of random sampling.

Answer
Strength

Minimizes bias and increases sample representativeness.

Term
Snowball Sampling

What is snowball sampling?

Answer
Definition

Participants recruit further participants from their social network, often used for hard-to-reach groups.

Term
Bias in Snowball Sampling

Why might snowball sampling be biased?

Answer
Weakness

It relies on social networks, which may not represent the entire population.

Term
Opportunity Sampling

Describe opportunity (convenience) sampling.

Answer
Definition

Researchers select participants who are readily available to them.

Term
Self-selected Sampling Weakness

What is a key weakness of self-selected sampling?

Answer
Weakness

It is biased because volunteers may differ systematically from non-volunteers.

Term
Sample Size

How does sample size affect research?

Answer
Effect

Larger samples increase reliability and the ability to detect real effects.

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📊 Sampling Techniques Quiz

1. What is the target population?

The target population is the whole group of interest for the research, not just the sample.

2. Which sampling technique gives every member an equal chance of selection?

Random sampling ensures all members have an equal probability of being chosen, reducing bias.

3. What is a main drawback of snowball sampling?

Snowball sampling relies on participants’ social connections, which may not reflect the wider population.

4. Why is sample size important?

Larger samples reduce random error, increasing the confidence in findings.

5. Which sampling method is most likely biased due to voluntary participation?

Volunteers may differ in key ways from those who do not volunteer, introducing bias.

📊 Results

  • Notes and Quiz
  • Psychology
  • A Level
  • Research Methods
  • OCR