sampling - populations and samples

Question 1

what is a population

Answer 1

a population is a large group of individuals that a particular research may be interested in studying, e.g. students attending colleges in the North West, children under six with autism, women in their thirties

this is called the target population

however for practical and economical reasons it is not possible to include all members of a target population in an investigation

Question 2

why do researchers select samples rather than investigation the whole target population

Answer 2

it is not practical and economical to include all members of a target population in an investigation.

to solve this, researchers selects a smaller group known as the sample

Question 3

what is an ideal sample

Answer 3

ideally, a sample that is drawn will be representative of the target population so that generalisation of findings becomes possible

This is very difficult to represent populations within a given sample.Therefore, a majority of sample contain some degree of bias

Question 4

what is generalisation

Answer 4

generalisation is the extent of which findings and conclusions from a particular investigation can be broadly applied to the population

This is only made possible if the sample is representative of the population

Question 5

how are samples selected

Answer 5

samples are selected using a sampling technique

the aim is to produce a representative sample

Question 6

what is random sampling

Answer 6

a sophisticated form of sampling

all members of the of the target population have an equal chance of being selected

Question 7

how do we select a random sample

Answer 7

Method:

1. complete list of all members of the target population is obtained
2. secondly, all of the names on the list are assigned a number
3. sample is generated through the use of some lottery method ( computer - based randomiser/ picking numbers from a hat)

Question 8

what is a systematic sample

Answer 8

in a systematic sample every nth numbs of the target population is selected
e.g. 3rd house on a street

Question 9

how is a systematic sample selected

Answer 9

a sampling frame is produced, which is a list of people in the target population organised into, for instance, alphabetical order

a sampling system is nominated (every nth number). This interval may be determined randomly to reduce researcher bias

the researcher works through the sapling frame until the sample is complete

Question 10

what is a stratified sample

Answer 10

a sophisticated form of sampling

it involves a composition of the sample which reflects the proportions of people in certain sub- groups (strata) within the target population/ wider population

Question 11

how is a stratified sample selected

Answer 11

1. the researcher first identifies the different strata that make up the population
2. proportions needed for the sample to be representative are worked out
3. participants that make up each stratum are selected using random sampling

Question 12

what is a opportunity sample

Answer 12

given that representative samples of the target population are so difficult to obtain, many researchers simply decide to select anyone who happens to be willing and available

Question 13

what is a volunteer sample

Answer 13

participants select themselves to be part of the sample (also referred to as self - selection)

in a volunteer sample, the researcher may place an advert in a newspaper or on a common room notice board

willing participates simply raise their hand when the researcher asks

Question 14

what is a strength of random sampling

Answer 14

free from research bias
- this is because the researcher has no influence over who is selected and this prevents the form choosing people they may support their hypothesis

Question 15

what are some limitations of random sampling

Answer 15

• difficult and time consuming to conduct
  e. g. a complete list of a target population may be extremely difficult to obtain
• the sample may be unrepresentative of the entire target population. However, due to the laws of probability, random sampling is still more Representative than opportunity sampling
• the participants may refuse to take part ( this may mean the researcher ends up with more of an volunteer sample

Question 16

what us a strength of systematic sample

Answer 16

it avoids researcher bias -once the system for selection has been established the researcher has no influence over who is chosen ( more so if the system is randomly selected)

Question 17

what is a limitation of a systematic sample

Answer 17

systematic sampling is fairly representative, however, it is possible to get e.g. an all male sample through systematic sampling ( if unlucky)

Question 18

what is a strength of a stratified sample

Answer 18

• avoids researcher bias
• produces a representative sample because it is designed to accurately reflect the composition of the population. This means generalistaion of the finding becomes possible

Question 19

what is a limitation of a stratified sample

Answer 19

• not perfect as the identified strata cannot reflect all the ways that people are different, so complete representation of the target population is not possible

Question 20

what are some strengths of a opportunity sample

Answer 20

• is convenient
• saves the researcher a good deal of time and effort and is much less costly in terms of time and money than, say, random sampling

Question 21

what is a limitation of a opportunity sample

Answer 21

random sampling suffers form two forms of bias:

• the sample is unrepresentative of the target population as it is drawn from a specific area. Therefore, the findings cannot be generalised to the target population
• the researcher has complete control over the selection of participants and , for instance, may avoid people they don’t like the look of (researcher bias)

Question 22

what is a strength of a volunteer sample

Answer 22

it is very easy as it requires minimum input from the researcher (“ they come to you”) and so is less time - consuming

Question 23

what is a limitation of t volunteer sample

Answer 23

volunteer bias is a problem as asking for volunteers may attract a certain “profile” of a person, that is, one who is helpful, keen and curious. This might affect how far findings can be generalised