AS Statistics: 1 Data Collection Flashcards

1
Q

What is a population?

A

The whole set of items that are of interest.

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2
Q

What is a census?

A

A measure of every member of a population.

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3
Q

What is a sample?

A

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

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4
Q

What are the advantages of a census?

A
  • It should give a completely accurate result.
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5
Q

What are the disadvantages of a census?

A
  • Time-consuming and expensive.
  • Cannot be used when the testing process destroys the item.
  • Hard to process a large quantity of data.
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6
Q

What are the advantages of a sample?

A
  • Less time consuming and expensive than a census.
  • Fewer people have to respond.
  • Less data to process than a census.
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7
Q

What are the 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

What are sampling units?

A

Individual units of a population.

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9
Q

What is a sampling frame?

A

When sampling units are individually named or numbered to form a list.

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10
Q

What is simple random sampling?

A

Where every sample has an equal chance of being selected.

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11
Q

What are the advantages of simple random sampling?

A
  • Free of bias.
  • Easy and cheap to implement for small populations and small samples.
  • Each sampling unit has a know and equal chance of selection.
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12
Q

What are the disadvantages of simple random sampling?

A
  • Not suitable when the population size or the sample size is large.
  • A sampling frame is needed.
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13
Q

What is systematic sampling?

A

When elements are chosen at regular intervals from an ordered list.

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14
Q

What are the advantages of systematic sampling?

A
  • Simple and quick to use.

- Suitable for large samples and large populations.

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15
Q

What are the disadvantages of systematic sampling?

A
  • A sampling frame is needed.

- It can introduce bias if the sampling frame is not random.

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16
Q

What is stratified sampling?

A

When the population is divided into mutually exclusive strata (e.g. males and females) and a random sample is taken from each.

17
Q

What are the advantages of stratified sampling?

A
  • Sample accurately reflects the population structure.

- Guarantees proportional representation of groups within a population.

18
Q

What are the disadvantages of stratified sampling?

A
  • Population must be clearly classified into distinct strata

- Selection within each stratum suffers from the same disadvantages as simple random sampling.

19
Q

What is quota sampling?

A

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

20
Q

What are the advantages of quota sampling?

A
  • Allows a small sample to still be representative of the population.
  • No sampling frame required.
  • Quick, easy and inexpensive.
  • Allows for easy comparison between different groups within a population.
21
Q

What are the disadvantages of quota sampling?

A
  • Non-random sampling can introduce bias.
  • Population must be divided into groups, which can be costly or inaccurate.
  • Increasing scope of study increase number of groups, which adds time and expense.
  • Non-responses are not recorded as such.
22
Q

What is opportunity sampling?

A

Taking the sample from people who are available at the time the study is carried out and who fit the criteria you are looking for.

Sometimes called convenience sampling.

23
Q

What are the advantages of opportunity sampling?

A
  • Easy to carry out.

- Inexpensive.

24
Q

What are the disadvantages of opportunity sampling?

A
  • Unlikely to provide a representative sample.

- Highly dependent on individual researcher.

25
Q

What are quantitative variables/data?

A

Variables/data associated with numerical observations.

26
Q

What are qualitative variables/data?

A

Variables/data associated with non-numerical observations.

27
Q

What are continuous variables?

A

Variables that can take any value in a given range.

28
Q

What are discrete variables?

A

Variables that can take only specific values in a given range.

29
Q

What can we tell from classes in frequency tables?

A
  • Class boundaries tell you the max and min values that belong to each class.
  • The midpoint is the average of the class boundaries.
  • The class width is the difference between the upper and lower class boundaries.
30
Q

What does the large data set show?

A

Consist of weather data samples provided by the Met Office for 5 UK weather stations and 3 overseas over 2 time periods.

31
Q

What were the time periods of the large data set?

A

May - Oct 1987.

May - Oct 2015.

32
Q

Where were the large data set samples taken?

A
  • Leuchars.
  • Leeming.
  • Heathrow.
  • Hurn.
  • Camborne.
  • Jacksonville.
  • Perth.
  • Bejing.
33
Q

What variables were measured as part of the large data set in the UK?

A
  • Daily mean temperature (ᵒC).
  • Daily total rainfall (mm).
  • Daily total sunshine.
  • Daily mean wind direction and wind speed (in knots: 1kn = 1.15mph) (also categorized according to the Beaufort scale).
  • Daily maximum gust (kn).
  • Daily maximum relative humidity (%).
  • Daily mean cloud cover (oktas).
  • Daily mean visibility (Dm).
  • Daily mean pressure (hPa).
34
Q

What variables were measured as part of the large data set overseas?

A
  • Daily mean temperature (ᵒC).
  • Daily total rainfall (mm).
  • Daily mean pressure (hPa).
  • Daily mean windspeed.