Up Learn – A Level Psychology (AQA) – research methods (part 1)
Summary of Sampling Methods
Most of the studies that you’ll see in psychology use volunteer and opportunity sampling. This is because they take much less time and effort than the other three types, and we usually don’t have a list of the entire population that we’re studying!
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More videos on Research Methods (Part 1):
What is a Sample? (free trial)
Types of Sampling: Volunteer Sampling (free trial)
Volunteer Sampling: Pros and Cons (free trial)
Types of Sampling: Opportunity Sampling (free trial)
Opportunity Sampling: Pros and Cons
Volunteer vs Opportunity Sampling (free trial)
Types of Sampling: Systematic Sampling (free trial)
Systematic Sampling: Pros and Cons (free trial)
Types of Sampling: Random Sampling (free trial)
Research Methods (Part 1)
2. Cause and Effect (free trial)
3. The Scientific Process (free trial)
4. The Scientific Process: Aims (free trial)
5. The Scientific Process: Hypothesis (free trial)
6. Independent and Dependent Variables (free trial)
7. Levels of the Independent Variable (free trial)
8. Operationalisation (free trial)
9. The Scientific Process: Methods (free trial)
10. The Scientific Process: Results & Conclusions (free trial)
2. Features of Science: Hypothesis Testing (free trial)
3. Features of Science: Empirical Evidence (free trial)
4. Features of Science: Falsifiability (free trial)
5. Features of Science: Replicability (free trial)
6. Features of Science: Control (free trial)
7. Control: Extraneous Variables (free trial)
8. Control: Confounding Variables (free trial)
9. Article – Extraneous vs Confounding Variables (free trial)
10. Features of Science: Objectivity (free trial)
11. Features of science: Theory construction (free trial)
2. Validity – Part 1 (free trial)
3. Validity – Part 2 (free trial)
4. Assessing Validity (free trial)
5. Assessing Validity: Face Validity (free trial)
6. Assessing Validity: Concurrent Validity (free trial)
7. Reliability – Part 1 (free trial)
8. Reliability – Part 2 (free trial)
9. Internal and External Reliability (free trial)
10. The Split-half Method (free trial)
11. The Test-retest Method (free trial)
2. Extraneous Variables: Participant Variables (free trial)
3. Extraneous Variables: Investigator Effects (free trial)
4. Investigator Effects: Researcher Expectations (free trial)
5. Extraneous Variables: Situational Variables (free trial)
6. Introduction to Demand Characteristics (free trial)
7. Situational Variables Can Be Demand Characteristics (free trial)
8. Investigator Effects Can Be Demand Characteristics (free trial)
9. Demand Characteristics: Influence on Behaviour (free trial)
10. Effects of Extraneous Variables on Validity and Reliability (free trial)
11. Controlling for Extraneous Variables: Standardisation (free trial)
12. When Can We Use Standardisation? (free trial)
13. Controlling Extraneous Variables: Matching (free trial)
14. Controlling Extraneous Variables: Random Allocation (free trial)
15. Blinding (free trial)
16. Single and Double Blinding (free trial)
17. Extraneous Variables: Summary (free trial)
2. What is Sampling? (free trial)
3. Types of Sampling: Volunteer Sampling (free trial)
4. Volunteer Sampling: Pros and Cons (free trial)
5. Types of Sampling: Opportunity Sampling (free trial)
6. Opportunity Sampling: Pros and Cons (free trial)
7. Volunteer vs Opportunity Sampling (free trial)
8. Types of Sampling: Systematic Sampling (free trial)
9. Systematic Sampling: Pros and Cons (free trial)
10. Types of Sampling: Random Sampling (free trial)
11. Random Sampling: Pros and Cons (free trial)
12. Types of Sampling: Stratified Sampling (free trial)
13. Stratified Sampling: How? (free trial)
14. Stratified Sampling: Pros and Cons (free trial)
15. Sampling Summary (free trial)
2. What is an Experiment? (free trial)
3. Types of Experiment: Laboratory Experiments (free trial)
4. Pros and Cons of Laboratory Experiments (free trial)
5. Types of Experiment: Field Experiments (free trial)
6. Pros and Cons of Field Experiments (free trial)
7. Types of Experiment: Quasi Experiments (free trial)
8. Pros and Cons of Quasi Experiments (free trial)
9. Types of Experiment: Natural Experiments (free trial)
10. Pros and Cons of Natural Experiments (free trial)
11. Types of Experiment: Summary (free trial)
12. Types of Experimental Design (free trial)
13. Matched Pairs Design (free trial)
14. Independent Groups Design (free trial)
15. Repeated Measures Design (free trial)
16. Repeated Measures: Limitations (free trial)
17. Repeated Measures: Counterbalancing (free trial)
18. Experimental Designs: Comparison (free trial)
19. Experimental Designs for Quasi and Natural Experiments (free trial)
2. What are Non-Experimental Methods? (free trial)
3. Single Variable Studies (free trial)
4. Correlational Studies: What is a Correlation (free trial)
5. Correlational Studies: Positive and Negative Correlations (free trial)
6. What is a Correlational Study (free trial)
7. Correlational Studies: Correlation is not Causation (free trial)
8. Correlational Studies: Pros and Cons (free trial)
9. Case Studies (free trial)
10. Pros of Case Studies (free trial)
11. Cons of Case Studies (free trial)
2. Methods of Data Collection (free trial)
3. Self-Report Technique (free trial)
4. Open and Closed Questions (free trial)
5. Strengths of Closed Questions over Open Questions (free trial)
6. Strengths of Open Questions over Closed Questions (free trial)
7. Structured and Unstructured Interviews (free trial)
8. Strengths and Weaknesses of Structured and Unstructured Interviews (free trial)
9. Problems with Self-Report Methods: Objectivity (free trial)
10. Problems with Self-Report Methods: Social Desirability Bias (free trial)
11. Questionnaires vs Interviews: Speed of Data Collection (free trial)
12. Questionnaires vs Interviews: Investigator Effects (free trial)
13. Questionnaires vs Interviews: Quality of Data (free trial)
14. Questionnaires vs Interviews: Biased Sampling (free trial)
We’ve now seen the five different types of sampling.
We’ve seen that volunteer and opportunity sampling are…
In volunteer sampling, the researcher posts an ad, and then people approach the researcher volunteering to be participants.
Whereas in opportunity sampling, the researcher directly approaches the participants, going for whoever is available and willing at the time.
They’re both quick and easy ways to sample! But, in both cases, the sample will not be very representative of the population. However, we know that…
However, we know that volunteer sampling is a bit easier than opportunity sampling.
And opportunity sampling is a bit more representative than volunteer sampling.
So, these two guys end up all the way down in this corner, like this
On the other hand, if we have a list of all the people in the population, we can do these other types of sampling:
Systematic sampling, where…
Systematic sampling is where the researcher picks every nth person from a list.
Or random sampling, where…
Random sampling is when a researcher chooses participants at random from a list of the entire population. This means that every member of the population has an equal chance of being a participant.
Now, in both cases, we’re picking from the whole population, so the samples are going to be far more representative than with volunteer and opportunity sampling.
But, with systematic sampling, if the list has a pattern that varies systematically, then the sample may not be totally representative. So the sample is less representative than with random sampling.
On the other hand…sometimes it’s more difficultto do random sampling, because…
Sometimes it’s more difficult to do random sampling, because you need to a way to randomise the list, either by putting names into a hat, or having a computer select random numbers. For instance, if you just have a hefty telephone book that’s not digitised, you’d need to assign a number to each entry which would take forever.
Whereas with systematic sampling, you could just pick every nth name, which is easier.
So, systematic sampling is a bit easier than random sampling.
Fifth and finally, we have stratified sampling, which is…
Stratified sampling is when researchers sample so that their sample has the same proportion of each subgroup as the total population.
Here we don’t necessarily need a list of the entire population, but we do need to know the proportion of each subgroup in the population.
With stratified sampling¸ the sample will represent all subgroups proportionately. So it’s the most representative type of sampling.
However, we need to know a lot about our population, making this more difficult than volunteer and opportunity sampling. And, because we need to divide our population into the important subgroups, there aremore steps involved than in random sampling…so it’s even more difficult. So it goes here.
And, there’s always a chance that we miss out an important subgroup by mistake, so, again, it’s still not totally representative.
For all these 3, we are sampling from the entire population, so our sample is going to be more representative.
However, they require knowledge of the whole population, like a list of everyone. So unfortunately, we often can’t use these types of sampling.
In psychology, we often just don’t have access to a list of the entire population that we’re studying.
For instance, Patty’s population is ‘depressed people’….there’s no way she can get a list of all depressed people!
Whereas other psychology studies might have a population like ‘children’…or ‘men’… or ‘Canadians’.
For these studies, it’s not possible to have a list of the whole population, so researchers can’t use systematic, random or stratified sampling.
So, most of the studies that you’ll see in psychology either use volunteer or opportunity sampling.
So, in summary, the five types of sampling are…
The five types of sampling are:
1. Volunteer sampling
2. Opportunity sampling
3. Systematic sampling
4. Random sampling
5. Stratified sampling
Where…
Volunteer sampling leads to the least representative sample. As we go in this direction, samples get more representative, until we get to stratified sampling, which is the most representative type of sampling.
However, in terms of difficulty…
Stratified sampling is the most difficult type of sampling to conduct – you need to decide on the most important subgroups in the population, and make sure your sample has the same proportion as the population!
As we go down, the types of sampling get easier, until we get to volunteer sampling, which is the easiest type of sampling.
So, most of the studies that you’ll see in psychology use…
Most of the studies that you’ll see in psychology use volunteer and opportunity sampling. This is because they take much less time and effort than the other three types.
And, we usually don’t have a list of the entire population that we’re studying!