sampling - populations and samples Flashcards

1
Q

what is a population

A

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

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2
Q

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

A

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

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3
Q

what is an ideal sample

A

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

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4
Q

what is generalisation

A

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

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5
Q

how are samples selected

A

samples are selected using a sampling technique

the aim is to produce a representative sample

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6
Q

what is random sampling

A

a sophisticated form of sampling

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

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7
Q

how do we select a random sample

A

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)
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8
Q

what is a systematic sample

A

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

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9
Q

how is a systematic sample selected

A

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

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10
Q

what is a stratified sample

A

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

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11
Q

how is a stratified sample selected

A
  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
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12
Q

what is a opportunity sample

A

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

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13
Q

what is a volunteer sample

A

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

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14
Q

what is a strength of random sampling

A

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

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15
Q

what are some limitations of random sampling

A
  • 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
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16
Q

what us a strength of systematic sample

A

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)

17
Q

what is a limitation of a systematic sample

A

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

18
Q

what is a strength of a stratified sample

A
  • 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
19
Q

what is a limitation of a stratified sample

A
  • 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
20
Q

what are some strengths of a opportunity sample

A
  • 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
21
Q

what is a limitation of a opportunity sample

A

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)
22
Q

what is a strength of a volunteer sample

A

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

23
Q

what is a limitation of t volunteer sample

A

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