Sample selection and techniques

Question 1

What is a random sample?

Answer 1

A sample of ppts produced using a random technique such that every member of the target population has an qual chance of being selected

Question 2

How do you carry out a random sampling technique?

Answer 2

Examples of random techniques include giving everyone in the target population a number, putting the numbers in a hat and drawing out the required number of ppts, or using a random number generator. Random number generators are pseudorandom techniques

Question 3

What are some positives of using random sampling techniques?

Answer 3

• Unbiased, all members of the target population, have an equal chance of selection. However, the researcher may end up with a biased sample because not all of the ppts who are identified agree to participate
• It is possible to choose a specific subgroup in the target population first, which makes it easier to randomly select ppts

Question 4

What are some negatives of using a random sampling technique?

Answer 4

• Takes more time and effort than other techniques because you need to obtain a list of all the member of your target population, then identify a sample and then contact the people identified and ask if they will take part.
• Random samples are often not random because not all the ppts identified can be accessed or agree to take part. Therefore, the final sample may be more like a volunteer or opportunity sample.

Question 5

What is a stratified sample?

Answer 5

Ppts are selected from different subgroups (strata) in the target population in proportion to the subgroup’s frequency in that population

Question 6

How do you carry out a stratified sampling technique?

Answer 6

Subggroups, such as age groups, are identified and the number in each subgroup in the target population is identified. This is represented as a percentage total of the whole population. For example, 30% of the target population might be 10-12 years old. Then 30% of ppts in the study should be in that age group. The researcher uses random selection to identify the right number of 10-12 year olds.

Question 7

What are some positives of using a stratified sample?

Answer 7

• This is the most representative of all sampling techniques because all subgroups are represented and these subgroups are represented in proportion to the numbers in the target population
• Specific subgroups can be chosen according to the variables considered to be important by the researcher. This increases control over possible extraneous variables

Question 8

What are some negatives of using stratified sample?

Answer 8

• The decision about which subgroups to use be biased, thus reducing the representativeness of the sample
• This method involves a very lengthy process and those ppts selected may not always agree to take part. This means that it is not a technique that is used much in psychological research. It is used when conducting opinion polls.

Question 9

What is a volunteer sample?

Answer 9

A sample of ppts produced by asking for people willing to take part.H

Question 10

How do you carry out a volunteer sample?

Answer 10

For example, advertise in a newspaper or a noticeboard

Question 11

What are some positives of using a volunteer sample?

Answer 11

• A convenient way to find willing ppts. Researchers need committed ppts for time consuming studies and ppts are less likely to drop out as they volunteered
• May be a good way to get a specialised group of ppts. This is called purposive sampling. For example, if you wanted to study the behaviour of medical students it would make sense to put an ad on the noticeboard of a medical school rather than standing around in a shopping centre hoping to find some medical students

Question 12

What are some negatives of using volunteer sample?

Answer 12

• Sample is biased because volunteer ppts are likely to be more highly motivated and with extra time on their hands than the population in general- volunteer bias
• Volunteers may also be more willing to be helpful and thus may be more prone to guessing the aim of the study and responding to demand characteristics

Question 13

What is an opportunity sample?

Answer 13

A sample of ppts produced by selecting people who are most easily available at the time of the study?

Question 14

How do you acquire an opportunity sample?

Answer 14

For example, ask people walking by you in the street or in your common room at school

Question 15

What are some positives of using an opportunity sample?

Answer 15

• The most convenient technique because it takes little preparation. You just use the first ppts you can find. This means it takes less time to locate your sample than if using one of the other techniques.
• It may be the only technique available because the whole target population cannot be listed (needed for random and stratified sampling)`

Question 16

What are some negatives of using an opportunity sample?

Answer 16

• Inevitably biased because the sample is drawn from a specific part of the target population which has unique characteristics and is not likely to be representative. For example, shoppers in a city centre on a Monday morning from a small part of the population, e.g. they are largely not people at work
• Ppts may refuse to take part so the final sample also has the weaknesses of a volunteer sample such as being more likely to response to demand characteristics.