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examBoard: AQA
examType: GCSE
lessonTitle: Target Populations and Samples
When psychologists conduct research, they rarely have the time or resources to study every single person they're interested in. Instead, they select a smaller group to represent the larger population. Understanding how this selection process works is crucial for evaluating psychological research.
Key Definitions:
Imagine trying to study all teenagers in the UK to understand their social media habits. There are about 4.3 million teenagers in the UK! It would take years and cost millions of pounds. Instead, psychologists study a smaller group (sample) and use their findings to make educated guesses about all teenagers (the target population).
Psychologists use different methods to select participants for their studies. Each method has its own strengths and weaknesses.
Every member of the target population has an equal chance of being selected. This is like putting everyone's name in a hat and picking out names randomly.
Example: Using a computer to randomly select 200 students from a school register of 1,000 students.
Strengths: Reduces bias, more likely to be representative of the population.
Weaknesses: Requires a complete list of the population, which is often difficult to obtain.
Selecting participants at regular intervals from a list. For example, selecting every 10th person from a list.
Example: From a list of 500 hospital patients, selecting patient #5, then #15, then #25 and so on.
Strengths: Simple to use, spreads the sample across the list.
Weaknesses: If there's a pattern in the list, it might create bias.
The population is divided into groups (strata) based on characteristics like age or gender, then participants are randomly selected from each group.
Example: If a school has 60% girls and 40% boys, a stratified sample of 100 students would include 60 girls and 40 boys.
Strengths: Ensures proportional representation of different groups.
Weaknesses: Requires knowledge of the proportion of each group in the population.
Selecting participants who are easily available or volunteer themselves.
Example: A psychologist asking people in a shopping centre to complete a questionnaire.
Strengths: Quick, easy and inexpensive.
Weaknesses: Likely to be biased, as certain types of people may be more willing to participate.
Participants recruit other participants for the study. This is useful for studying hard-to-reach groups.
Example: Studying former gang members by finding one participant who then introduces researchers to others.
Strengths: Helps access difficult-to-reach populations.
Weaknesses: Sample may be limited to people in the same social network.
Participants choose to take part in the study after seeing an advertisement or announcement.
Example: Posting a study advertisement on social media and accepting anyone who responds.
Strengths: Easy to gather participants, especially for sensitive topics.
Weaknesses: Volunteers may have specific motivations or characteristics that make them unrepresentative.
The choice of sampling method depends on several factors:
Random or systematic sampling is best when you want to make claims about the general population.
Stratified sampling works well when you need to ensure certain groups are represented.
Snowball or opportunity sampling may be the only practical options for studying hidden populations.
A key concern in sampling is whether your sample truly represents the target population. If it doesn't, your findings may not be valid.
Common Sources of Sampling Bias:
In 1936, the Literary Digest magazine predicted that Republican Alf Landon would win the US presidential election by a landslide. Instead, Democrat Franklin D. Roosevelt won by one of the largest margins in history.
What went wrong? The magazine sent surveys to people on subscription lists, telephone directories and car registration lists. This created a biased sample that over-represented wealthy Americans (who tended to vote Republican) during the Great Depression. This famous polling disaster shows how important proper sampling is!
The number of participants in your sample (sample size) affects how confident you can be in your results.
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Disadvantages:
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When reading about psychological research, always ask yourself these questions:
Imagine you're designing a study on teenage social media use. If you only sample students from one private school in London, can you generalise your findings to all UK teenagers? Probably not! Your sample wouldn't include teenagers from different socioeconomic backgrounds, rural areas, or those who don't attend school. This shows why careful consideration of sampling is crucial for valid research.
Sampling is a crucial aspect of psychological research. The way participants are selected can significantly impact the validity and reliability of findings. While random and stratified sampling methods tend to produce more representative samples, practical constraints often lead researchers to use more convenient methods. Understanding these different approaches helps us critically evaluate psychological research and its applicability to the wider population.
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