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Edexcel A Level Maths > Statistics: Sampling > Flashcards

Statistics: Sampling Flashcards

1
Q

What is a Census?

A

A census measures or observes every member of a population

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2
Q

What is a Sample?

A

A sample is a selection of observations taken from a subset of a population. It’s used to find out more information about a population as a whole.

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3
Q

Advantages / Disadvantages of a Census

A

Advantage:
- Results should be completely accurate

Disadvantages:
- Time consuming and expensive
- Hard to process large quantity of data

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4
Q

Advantages / Disadvantages of a Sample

A

Advantages:
- Less time consuming and cheaper
- Few people have to respond

Disadvantages:
- Data may not be as accurate
- Sample may not be large enough to give info about small subgroups of a population

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5
Q

What is Random sampling?

A

Each member of a population has an equal chance of being selected.

The three types of Random Sampling:
- Simple random sampling
- Systematic sampling
- Stratified

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6
Q

What is Simple random sampling?

A

Every sample of size n has an equal chance of being selected.

A Simple random sample can be taken by using:
- A calculator or random number generator
- Lottery sampling

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7
Q

How does a Calculator or Random number generator work?

A
  1. Number each member from 1 to n (size of sample)
  2. Use a calculator / random number generator to generate x random numbers between 1 to n
  3. Select the members who correspond to the numbers.
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8
Q

How does Lottery Sampling work?

A
  1. Write the name of members on identical cards
  2. Place them in a hat
  3. Draw up x cards and select these members.
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9
Q

Advantages of Simple random Sampling

A
  • Free of bias
  • Easy and cheap for small samples and populations
  • Each sampling unit has a known and equal chance of selection
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10
Q

Disadvantages of Simple random Sampling

A
  • Not suitable for large samples and populations
  • Sampling frame needed
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11
Q

What is Systematic sampling?

A

The required elements are chosen at regular intervals from an ORDERED list

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12
Q

Advantages of Systematic sampling

A
  • Simple and quick to use
  • Useful for large samples and populations
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13
Q

Disadvantages of Systematic sampling?

A
  • Sampling frame needed
  • Bias introduced if sampling frame is not random
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14
Q

What is Stratified sampling?

A

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

Num sampled in a stratum = number in stratum

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15
Q

Disadvantages of Systematic sampling

A
  • A sampling frame is needed
  • Bias introduced if sampling frame is not random
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16
Q

What is Stratified sampling?

A

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

Number sampled in statum:
(num in stratum / num in population) x overall sample size

17
Q

Advantages of Stratified sampling

A
  • Sample accurately reflects population structure
  • Proportional representation of group within population
18
Q

Disadvantages of Stratified sampling

A
  • Population must be clearly classified into distinct strata
  • same disadvantages as simple random sampling within each stratum
19
Q

What is Quota sampling?

A

An interviewer or researcher selects a sample that reflects the characteristics of the whole population

20
Q

Advantages of Quota sampling

A
  • No sampling frame required
  • Quick, easy and inexpensive
  • Allows small sample to still be representative of the population
21
Q

Disadvantages of Quota sampling

A
  • Non-random sampling can introduce bias
  • Population must be divided into groups -> can be costly or inaccurate
22
Q

What is Opportunity sampling?

A

Sample is taken from people who are available at the time of study and who fits the criteria you’re looking for

23
Q

Advantages of Opportunity sampling

A
  • Easy and inexpensive
24
Q

Disadvantages of Opportunity sampling

A
  • Unlikely to provide a representative result
  • Highly dependent on individual researcher

Edexcel A Level Maths (2 decks)

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