Stat: Data Collection

Question 1

Primary data

Answer 1

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

Question 2

Secondary Data

Answer 2

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

Question 3

Population

Answer 3

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

Question 4

Census

Answer 4

Every member of the population is observed or measured.

Question 5

Sample

Answer 5

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

Question 6

Sample Survey

Answer 6

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

Question 7

Sampling Unit

Answer 7

An individual member of the population.

Question 8

Sampling Frame

Answer 8

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

Question 9

Random Sample meaning

Answer 9

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

Question 10

Simple Random Number Sampling

Answer 10

• 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)

Question 11

Systematic Sampling

Answer 11

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)

Question 12

Stratified Sampling

Answer 12

• 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.

Question 13

Stratified sampling formula

Answer 13

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

Question 14

Quota Sampling

Answer 14

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

Question 15

Opportunity sampling

Answer 15

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

Question 16

Census Advantages

Answer 16

• It should give a completely accurate result.

Question 17

Census Disadvantages

Answer 17

• 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.

Question 18

Sample survey Advantages

Answer 18

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

Question 19

Sample survey Disadvantages

Answer 19

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.

Question 20

Random sampling with replacement

Answer 20

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.

Question 21

Sampling without replacement

Answer 21

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.

Question 22

Quota sampling advantages

Answer 22

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

Question 23

Quota sampling disadvantages

Answer 23

• 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

Question 24

Opportunity sampling advantages

Answer 24

• easy to carry out
• cheap

Question 25

Opportunity sampling disadvantages

Answer 25

- unlikely to provide a representative sample - dependent on individual researcher

Question 26

Measures of location

Answer 26

Comparing mean and median

Question 27

Measures of spread

Answer 27

Standard deviation and IQR

Question 28

Which measures to use together?

Answer 28

Mean and standard deviation Median and IQR

Question 29

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

Answer 29

- There’s fewer large distances - The distribution is positively skewed

Question 30

The higher the standard deviation/IQR…

Answer 30

The greater the spread

Question 31

What month is least sunshine?

Answer 31

October since least sunshine

Question 32

A stratified sample must have...

Answer 32

a sampling frame

Question 33

Difference between stratified sampling and quota sampling

Answer 33

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

Question 34

When to use median and IQR?

Answer 34

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

Question 35

How will extra values below the medium affect values?

Answer 35

- Q2 will be lower - Q3 will be lower

Question 36

Statistic

Answer 36

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

Question 37

Explain what you understand by the sampling distribution of Y

Answer 37

The probability distribution

Question 38

What’s not a statistic?

Answer 38

The equation with unknown parameters

Question 39

Sampling distribution

Answer 39

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

Question 40

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

Answer 40

- it’s a piece of data so we should consider all data - it’s an outliers that could effect the results

Question 41

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

Answer 41

0-500m

Question 42

Use mean or median to analyse data

Answer 42

If outliers use median since it will affect mean

Question 43

Quota vs stratified

Answer 43

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

Question 44

Scatter diagram

Answer 44

X

Question 45

High standard deviation

Answer 45

data are more spread out

Question 46

Low standard deviation

Answer 46

clustered around the mean

Question 47

Extrapolation

Answer 47

estimating an unknown value based on extending the values

Question 48

Dangers of extrapolation

Answer 48

- 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.

Question 49

How t9 know is PMCC value is wrong

Answer 49

If it is greater than 1

Question 50

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

Answer 50

- daily wind speed (Beaufort) since it is qualitative data - rainfall (since not symmetric)

Question 51

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

Answer 51

Too little days measures or data

Question 52

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

Answer 52

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

Question 53

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

Answer 53

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

Question 54

Big IQR/range or spread

Answer 54

Larger standard deviation

Question 55

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

Answer 55

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

Question 56

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

Answer 56

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

Question 57

Non random sampling methods

Answer 57

Opportunity or quota

Question 58

Why might a stratified random sampling not be used?

Answer 58

It is not possible to have a sampling frame

Question 59

Qualitative variables

Answer 59

Wind speed

Question 60

Smaller mean but larger standard deviation