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A - level Maths > STATISTICS - Data collection > Flashcards

STATISTICS - Data collection Flashcards

1
Q

Definition of a population

A

The whole set of items that are of interest

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2
Q

Definition of a sample

A

Some subset of the population intended to represent the population

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3
Q

Definition of a sampling unit

A

Each individual thing in the population that can be sampled

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4
Q

Definition of a sampling frame

A

A list of all the sampling units

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5
Q

Definition of a census

A

Data collected from the entire population

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6
Q

Advantages of a census

A
  • Should give completely accurate results
  • More reliable
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7
Q

Disadvantages of a census

A
  • More time consuming
  • More expensive
  • Cannot be used when testing involves destruction
  • Large volume of data to process
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8
Q

Advantages of a sample

A
  • Cheaper
  • Quicker
  • Less data to process
  • Possible when data involves destruction
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9
Q

Disadvantages of a sample

A
  • Data may not be accurate
  • Data may not be large enough to represent small sub-groups
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10
Q

What is qualitative data?

A

Non - numerical values

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11
Q

What is quantitative data?

A

Numerical values

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12
Q

What is discrete data?

A

Can only take specific values

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13
Q

What is continuous data?

A

Can take any decimal values

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14
Q

What are the types of sampling?

A

Random vs Non-random sampling

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15
Q

What are the 3 types of random sampling?

A
  • Simple random sample
  • Systematic sampling
  • Stratified sampling
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16
Q

What are the 2 types of non-random sampling?

A
  • Quota sampling
  • Opportunity sampling
17
Q

How would you carry out a simple random sample?

A
  • List all members of the population and assign them a number from 1-‘n’ to each member
  • Use a random number generator to select ‘k’ unique numbers (ignore repeats)
  • Select the corresponding members of the population which match the numbers generated to form the sample
18
Q

Advantages of simple random sampling?

A
  • Bias free
  • Easy and cheap to implement
  • Each number has a known equal chance of being selected
19
Q

Disadvantages of simple random sampling?

A
  • Not really suitable when population size is really large
  • Sampling frame needed
20
Q

How would you carry out a systematic sample?

A
  • Take every Kth element where:
    > K = population size/sample size
  • List all the members of the population and assign a number from 1-‘n’ to each
  • Use a random number generator to select and number between 1 and K (starting point)
  • Then select every Kth person to form the sample
21
Q

Advantages of systematic sampling?

A
  • Simple and quick to use
  • Suitable for large samples/population
22
Q

Disadvantages of systematic sampling?

A
  • Sampling frame needed
  • Can introduce bias if sampling frame is not random
23
Q

How would you carry out a stratified sample?

A

For each strata, calculate:
- size of strata/population size x sample size
- Carry out a simple random sample for each strata

24
Q

Advantages of stratified sampling?

A
  • Reflects population structure
  • Guarantees proportional representation of groups within population
25
Q

Disadvantages of stratified sampling?

A
  • Population must be clearly classified into distinct data
  • Selection within each stratum suffers from same disadvantages as simple random sampling
26
Q

How would you carry out a quota sample?

A
  • Population is divides into groups according to characteristics
  • A quota of items/people in each group is set to try and reflect the group’s proportion in the whole population
  • Interviewer selects the actual sampling units
27
Q

Advantages of quota sampling?

A
  • Allows small sample to still be representative of population
  • No sampling frame required
  • Quick, easy and inexpensive
  • Allows for easy comparison between different groups in the population
28
Q

Disadvantages of quota sampling?

A
  • Non random sampling can introduce bias
  • Population must be divided into groups, which can be costly and inaccurate
  • Increasing scope of study increases number of groups, adding time/expense
  • Non-responses are not recorded
29
Q

How would you carry out an opportunity sample?

A

Sample taken from people who are available at time of study, who meet criteria

30
Q

Advantages of opportunity sampling?

A
  • Easy to carry out
  • Inexpensive
31
Q

Disadvantages of opportunity sampling?

A
  • Unlikely to provide a representative sample
  • Highly dependent on individual researcher
32
Q

Give an example of when a census would be practical and useful (PPQ)

A

A small company wishes to ask about their employee’s opinions about pension schemes

33
Q

Give an example of when a census would be impractical and therefore a sample would be needed (PPQ)

A

A city council wants to find out what its residents feel about their recycling centres

34
Q

Give an example of how you could use simple random sampling to select a sample of 50 people from an alphabetical list of the 2500 inhabitants of a particular district (PPQ)

A
  • Allocate each person a number starting at 1 and ending at 2500
  • Use random number tables to select 50 random numbers between 1 and 2500

A - level Maths (2 decks)

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