Sampling

Question 1

target population

Answer 1

population is the group of individuals that a researcher wishes to study. For example, if a researcher was investigating “attitudes of Worcester Sixth Form College students to smoking”, then the target population would be all Worcester Sixth Form College students.

In most studies, it is not possible to study all members of the target population, so researchers select a sample. This is a group taken from the target population that should be representative so that generalisations can be made.

Question 2

5 sampling techniques

Answer 2

random, systematic, stratified, opportunity and volunteer sampling

Question 3

implications associated with using each of these sampling techniques

Answer 3

*Bias – whereby the sample selected is distorted in some way and does not represent the target population.

*Generalisation – results from the sample can be applied to the target population. This is usually only possible if an unbiased sample has been selected.

Question 4

random sampling

Answer 4

In random sampling, every member of the target population has an equal chance of being selected for the sample. If you have a fairly small number of individuals in your target population, then this could be done easily by writing the name of each member of the population on a piece of paper and putting the names into a hat (or assigning numbers to each name and writing the numbers on pieces of paper). Without looking, you then draw names from the hat until your sample has been selected.

For example, if your target population was a class of 20 A’ Level History students and you wanted 6 students in your sample, then you would assign numbers 1 to 20 for each of the History students, put the numbers 1 to 20 in a hat and then pick out 6 numbers. Your sample would include the students who were assigned the numbers you picked

Question 5

random sampling strength

Answer 5

There is no bias in the selection of this sample therefore increasing the chances that the sample will be representative of the target population.

As the sample should be fairly representative, results will be generalisable to the target population.

Question 6

random sampling weakness

Answer 6

The sample could still be biased - an unbiased selection process does not mean an unbiased sample. During random sampling, only females may be selected making the sample unrepresentative of the target population.

It is not always practical to use this technique. For example, when the target population is large or when a small sample is required.

Question 7

systematic sampling

Answer 7

This technique involves taking every nth member of the target population to form the sample. This could be every 10th person on a school register or every 3rd house on a street.

For example, suppose you need 20 participants from your college and the college has 1000 students. 1000 divided by 20 is 50 - therefore you select every 50th name from an alphabetical list of students in your college.

Question 8

systematic sampling strengths

Answer 8

There is no bias in the selection of this sample therefore increasing the chances that the sample will be representative of the target population.

As the sample should be fairly representative, results will be generalisable to the target population.

Question 9

systematic sampling weakness

Answer 9

Not truly unbiased unless you select your starting point randomly and then select every nth person from this point.

Question 10

stratified sampling

Answer 10

This is a small-scale reproduction of the target population. Taking a sample involves dividing the target population into ‘strata’ or categories important for the study (e.g., age, gender, religious background, etc.). Using random selection, participants are selected within each category in the proportions that they exist in the target population.

For example, suppose your college student population is 55% female and 45% male and you need to select a stratified sample of 20 students. You could place names of all the female students in one hat and randomly select 11 names; you would then place the names of all the male students in another hat and randomly select 9 names. These 20 participants would form your sample.

Question 11

stratified sampling strengths

Answer 11

There is no bias in the selection of this sample. Random selection is used on the relevant categories within a target population. This therefore increases the chance of the sample being representative of the target population.

The sample should be fairly representative as selection is taken from the main categories or strata within the target population. This would allow generalisations to be made.

Question 12

stratified sampling weaknesses

Answer 12

This type of sampling requires a detailed knowledge of the target population, and this knowledge may not be available.

Dividing the target population into categories and then randomly selecting the sample is a time-consuming technique.

Question 13

opportunity sampling

Answer 13

In opportunity sampling, the researcher decides on the type of participant needed and approaches anyone who appears suitable until sufficient numbers have been obtained.

For example, you might ask students present in the college canteen during one lunchtime to take part in your study. Those who form your sample are those who happen to be around and available at the time.

Question 14

opportunity sampling strength

Answer 14

It is relatively quick and convenient to collect an opportunity sample as the researcher is not required to identify all the members of the target population, as would be needed in a random sample.

Question 15

opportunity sampling weaknesses

Answer 15

The sample is likely to be biased as it excludes certain types of participants (e.g., those who are not around when the researcher is selecting the sample). This makes it unrepresentative of the target population.

If the sample is biased, then it is not possible to make generalisations to the target population.

Question 16

volunteer sampling

Answer 16

In volunteer sampling, the researcher advertises for participants. In this sampling method participants choose themselves by replying to the advert.

For example, you might place an advert in a newspaper, doctor’s surgery or leisure centre. Those who respond to your advert form your sample.

Question 17

Volunteer Sampling strengths

Answer 17

Creating a sample is fairly easy in comparison to other techniques, as the participants volunteer themselves.

As the participants volunteer themselves, there is less chance of them deliberately sabotaging the study.

Question 18

Volunteer Sampling weaknesses

Answer 18

The sample is likely to be biased as volunteers tend to be a certain type of individual (e.g., those who are interested in psychology or those who need the money offered for taking part in the study). This makes it likely to be unrepresentative of the target population.

If the sample is biased, then it is not possible to make generalisations to the target population.