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A Level Mathematics > Sampling > Flashcards

Sampling Flashcards

1
Q

Sample

A

A selection of observations taken from a subset of the population which is used to find out more information about the population as a whole.

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2
Q

Population

A

The set of all the items that are of interest.

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3
Q

Census

A

A census measures or observes every member of a population.

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4
Q

Advantages of a census

A

Should give a completely accurate result.

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5
Q

Disadvantages of a census

A
  • time consuming and expensive
  • cannot be used when the testing process destroys the item
  • hard to process large quantity of data
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6
Q

Advantages of a sample

A
  • less time consuming and expensive than a census
  • fewer people have to respond
  • less data than a census
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7
Q

Disadvantages of a sample

A
  • the data may not be as accurate
  • the sample may not be large enough to give information about small sub groups of the population
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8
Q

Individual units of a population are known as…

A

Sampling units

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9
Q

Often, sampling units of a population are individually numbered to form a list called a…

A

Sampling frame

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10
Q

What happens in lottery sampling?

A

The members of the sampling frame could be written on tickets and placed into a ‘hat’. The required number of tickets would then be drawn out.

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11
Q

Simple random sampling

A

Every member of the population has an equal probability of being selected for the sample.

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12
Q

Systematic sampling

A

The required elements are chosen at regular intervals from an ordered list, but the first one has to be chosen at random.

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13
Q

Stratified sampling

A

The population is divided into mutually exclusive strata. Proportional representation is used to make each subgroup proportional with the size of the subgroup.

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14
Q

Formula for number of people we should use from each stratum

A

Number in stratum/ number in population x overall sample size

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15
Q

Simple random sampling: random number generator

A

Number each member 1-100. Use a random number generator to generate x random numbers between 1-100. Select the members who correspond to the numbers.

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16
Q

Advantages of simple random sampling

A
  • free of bias
  • easy and cheap for small samples and populations
  • each sampling unit has an equal chance of selection
17
Q

Disadvantages of simple random sampling

A
  • not suitable for large samples and populations
  • sampling frame needed
18
Q

Systematic sampling

A

The required elements are chosen at regular intervals from an ordered list, the first interval is chosen at random.

19
Q

Advantages of systematic sampling

A
  • simple and quick to use
  • suitable for large samples and large populations
20
Q

Disadvantage of systematic sampling

A
  • a sampling frame is needed
  • bias introduced if sampling frame is not random
21
Q

Stratified sampling

A

The population is divided into mutually exclusive strata and a random sample is taken from each

  • number sampled in a stratum= number in stratum/ number in population x overall sample size
22
Q

Advantages of stratified sampling

A
  • sample accurately reflects population structure
  • proportional representation of group within population
23
Q

Disadvantages of stratified sampling

A
  • population must be clearly classified into distinct strata
  • same disadvantages as simple random sampling within each stratum
24
Q

Quota sampling

A

Similar to stratified, but the quota of items to be included from the different subgroups isn’t necessarily proportional. It also doesn’t require a random sample within the subgroup, so bias is extremely likely.

25
Q

Opportunity sampling

A
  • also known as convenience sampling
  • can be used even if the size of the population isn’t known
26
Q

Cluster sampling

A
  • population is divided into subgroups which are each reasonably representative
  • cluster sampling means taking a sample from just a few of these subgroups
  • e.g. if you wanted a sample of year 11 students, you might take a sample from 2/3 different schools
  • may only be appropriate if you were investigating something that is unlikely yo be affected by the school a student attends

A Level Mathematics (6 decks)

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