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Maths > Stat: Data Collection > Flashcards

Stat: Data Collection Flashcards

1
Q

Primary data

A

The data is collected by, or on behalf of, the person who is going to use the data.

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2
Q

Secondary Data

A

The data is not collected by, nor on behalf of, the person who is to use the data. The data are second hand.

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3
Q

Population

A

The whole set of individuals or items that are of interest.

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4
Q

Census

A

Every member of the population is observed or measured.

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5
Q

Sample

A
  • A carefully selected sub-set of the population.
  • It should be representative of the population.
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6
Q

Sample Survey

A

This where information about the population is found out from the information obtained from sample.

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7
Q

Sampling Unit

A

An individual member of the population.

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8
Q

Sampling Frame

A

A list identifying every single sampling unit that is in the population.

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9
Q

Random Sample meaning

A

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

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10
Q

Simple Random Number Sampling

A
  • Each item or individual is given a number.
  • Selection is then carried out via random number tables or generators.
  • (random numbers generated using a calculator or Electronic random number indicating Equipment)
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11
Q

Systematic Sampling

A

Elements are chosen at regular intervals from an ordered list.
- (if sample size is 20 from a population of 100, you’d take every fifth person 100/20)

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12
Q

Stratified Sampling

A
  • Population is divided into mutually exclusive strata.
  • A simple random sample is taken from each strata.
  • The proportion of each strata in the sample is the same as that in the population.
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13
Q

Stratified sampling formula

A

the no. sampled in a stratum= no. in stratum/ no. in a population x overall sample size

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14
Q

Quota Sampling

A
  • Population is dvided into groups of gender, social class, etc.
  • Number of individuals selected is set to reflect the population.
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15
Q

Opportunity sampling

A
  • taking the sample from people who are available at the time the study is carried out
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16
Q

Census Advantages

A
  • It should give a completely accurate result.
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17
Q

Census Disadvantages

A
  • It is time consuming and expensive.
  • It cannot be used when testing leads to destruction (e.g testing lifetime of batteries)
  • lots of data, so can be difficult to process.
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18
Q

Sample survey Advantages

A
  • It is cheaper than a Census.
  • Results are quicker compared to a Census.
  • Less data to deal with than a Census.
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19
Q

Sample survey Disadvantages

A

The data may not be as accurate, so sample is not representative of the population.
- Sample may not be large enough to provide information about the small sub- groups of the population.

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20
Q

Random sampling with replacement

A

Each unit is replaced back into the population before the next selection is made. So each unit can appear more than once in the sample.

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21
Q

Sampling without replacement

A

If a unit is selected, it’s not replaced. So for each draw only the sampling units that have not been selected previously are eligible for the next draw.

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22
Q

Quota sampling advantages

A
  • quick since a representative sample can be achieved with a small sample size
  • cheap
  • easy
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23
Q

Quota sampling disadvantages

A
  • can introduce bias by person picking sampling units
  • inaccurate since it’s impossible to estimate the sampling errors as the process is not a random process
  • non responses are not recorded
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24
Q

Opportunity sampling advantages

A
  • easy to carry out
  • cheap
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25
Q

Opportunity sampling disadvantages

A
  • unlikely to provide a representative sample
  • dependent on individual researcher
26
Q

Measures of location

A

Comparing mean and median

27
Q

Measures of spread

A

Standard deviation and IQR

28
Q

Which measures to use together?

A

Mean and standard deviation
Median and IQR

29
Q

What does it mean if the median is greater than the mean

A
  • There’s fewer large distances
  • The distribution is positively skewed
30
Q

The higher the standard deviation/IQR…

A

The greater the spread

31
Q

What month is least sunshine?

A

October since least sunshine

32
Q

A stratified sample must have…

A

a sampling frame

33
Q

Difference between stratified sampling and quota sampling

A

Same method but
Stratified vs quota
- sampling frame is required vs not required
- random sampling error can be estimated vs cannot be estimated

34
Q

When to use median and IQR?

A

if there are outliers (the data is skewed) then use median and IQR since this will affect mean and standard deviation

35
Q

How will extra values below the medium affect values?

A
  • Q2 will be lower
  • Q3 will be lower
36
Q

Statistic

A

A random variable that is a function of a random sample that contains no unknown parameters

37
Q

Explain what you understand by the sampling distribution of Y

A

The probability distribution

38
Q

What’s not a statistic?

A

The equation with unknown parameters

39
Q

Sampling distribution

A

the values of a statistic and the associated probabilities is a sampling distribution

40
Q

Give a reason we should include outliers and a reason why we shouldn’t

A
  • it’s a piece of data so we should consider all data
  • it’s an outliers that could effect the results
41
Q

The range of distances in m that corresponds to the recorded value 0 for daily mean visibility

A

0-500m

42
Q

Use mean or median to analyse data

A

If outliers use median since it will affect mean

43
Q

Quota vs stratified

A

Stratified: Take a (simple) random sample from (mutually exclusive) groups of the population
Sample sizes within strata in strict proportion to numbers in each strata in the population
Quota: Non-random sampling
from groups of the population

44
Q

Scatter diagram

A

X

45
Q

High standard deviation

A

data are more spread out

46
Q

Low standard deviation

A

clustered around the mean

47
Q

Extrapolation

A

estimating an unknown value based on extending the values

48
Q

Dangers of extrapolation

A
  • can be unreliable, since trend might not continue (especially when there are disparities in the existing data sets)
    . Extrapolation doesn’t account for qualitative values that can trigger changes in future values within the same observation. It hardly accounts for causal factors in the observation.
49
Q

How t9 know is PMCC value is wrong

A

If it is greater than 1

50
Q

State two variables from the large data set that are not suitable to be modelled by a normal distribution.

A
  • daily wind speed (Beaufort) since it is qualitative data
  • rainfall (since not symmetric)
51
Q

Comment on the suitability of Sara’s sampling method of this study

A

Too little days measures or data

52
Q

Suggest how Sara could make better use of the large data set for her study

A

Use more data from more of the UK locations and more of the months

53
Q

From your knowledge of the large data set, explain why this process may not generate a large enough sample size

A

In the large data set, some days might have gaps because the data was not recorded

54
Q

Big IQR/range or spread

A

Larger standard deviation

55
Q

If median increases but mean (22.5) is same. Suggest values

A

Both values must be greater than median and values must add to 45

56
Q

Additional values are added. Explain why the standard deviation will be lower

A

Both values must be less than 1 standard eviction from the mean

57
Q

Non random sampling methods

A

Opportunity or quota

58
Q

Why might a stratified random sampling not be used?

A

It is not possible to have a sampling frame

59
Q

Qualitative variables

A

Wind speed

60
Q

Smaller mean but larger standard deviation

A

Maths (5 decks)

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