Statistics - Data collection Flashcards Preview

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Flashcards in Statistics - Data collection Deck (53):
1

What is a population?

The whole set of items that are of interest

2

What is a census?

A survey that observes/measures every member of a population

3

What is a sample?

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

4

What is the advantage of a census?

Should give a completely accurate result

5

What are the disadvantages of a census?

Time consuming & expensive
Hard to process large quantities of data
Cannot be used when testing process destroys item

6

What are the advantages of taking a sample?

Less time consuming & expensive than a census
Fewer people have to respond
Less data to process

7

What are the disadvantages of taking a sample?

Data may not be accurate
Sample maybe not large enough to represent all small sub-groups in the population

8

What happens as the sample size increase?

The more accurate it is
More representative of the sample

9

What is the individual units of a population called?

Sampling units

10

What are done to sampling units in order to distinguish them?

They are individually named or numbered to form a list

11

What is a statistic?

A value taken from a single sample

12

What is a sampling frame?

A list of the sample units

13

What happens in random sampling?

Each member of the population has an equal chance of being selected

14

What are the advantages of using random sampling?

Representative of the population
Removes bias

15

What are the three methods of random sampling?

Simple random sampling
Systematic sampling
Stratified sampling

16

How can you perform simple random sampling?

Number each sampling unit
Random number generator or numbers put into a "hat" and chosen at random

17

What are the advantages of simple random sampling?

Free of bias
Easy and cheap for small populations/samples
Each sampling unit has a known/equal chance of selection

18

What are the disadvantages of simple random sampling?

Not suitable when population/sample size is large
Sampling frame is needed

19

What is systematic sampling?

Required elements are chosen at regular intervals from an ordered list
E.g Data taken every nth value

20

What are the advantages of systematic sampling?

Simple and quick to use
Suitable for large samples/populations

21

What are the disadvantages of systematic sampling?

Sampling frame is needed
Can introduce bias if sampling frame is not random

22

What is stratified sampling?

Population is divided into mutually exclusive strata, and a random sample is taken from each
Strata example - male & female

23

What rules should be followed for obtaining strata?

Proportion of each strata should be the same

24

What is the formula to calculate the number of people should be sampled from each strata?

Number sampled in strata = (number in strata / number in population) x overall sample size

25

What are the advantages of stratified sampling?

Sample accurately reflects the population structure
Guarantees proportional representation of groups within a population

26

What are the disadvantages of stratified sampling?

Population must be clearly classified into distinct strata
Selection within each stratum has disadvantages of simple random sampling

27

What are the two types of non-random sampling?

Quota sampling
Opportunity sampling

28

What is quota sampling?

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

29

How is quota sampling done?

Population is divided into groups by an interviewer due to characteristics
Continues until quota is full

30

What happens with quota sample sizes?

Size of each group determines proportion of sample that should have that characteristic
Quotas will have a limit - if full the person's data is dismissed

31

What are the advantages of quota sampling?

No sampling frame required
Quick, easy and inexpensive
Small sample still representative of population
Allows easy comparison between different groups

32

What are the disadvantages of quota sampling?

As non-random it introduces bias
Population division can be costly or inaccurate
Non-responses are not recorded
Increases groups so adds time and expensive

33

What is opportunity sampling?

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

34

What are the advantages of opportunity sampling?

Easy to carry out
Inexpensive

35

What are the disadvantages of opportunity sampling?

Highly dependent on individual researches
Unlikely to provide representative sample

36

What is opportunity sampling also known as?

Convenience sampling

37

What is quantitative variables/data?

Data/variables associated with numerical observations

38

What is qualitative variables/data?

Data/variables associated with non-numerical observations

39

What is a continuous variable?

A variable that can be given in any range
E.g 2 seconds, 2.3 s, 2.02 s

40

What is a discrete variable?

A variable that can only be specific values
E.g can't have 2.65 people

41

What are the groups in grouped frequency tables called?

Classes

42

What face value data can be found using a grouped frequency table?

Class boundaries tell you max and min values in the class
Midpoint is the average of the class boundaries
Class width is the difference between higher and lower class boundaries

43

What large data sets will be provided?

Data about the weather, location, about different places around the world

44

What is the daily mean temperature?

°C
Average of hourly temp readings

45

What is the daily total rainfall?

Includes solid precipitation
Melted before being included in measurements
Less than 0.05mm recorded as "trace" or "tr"

46

What is daily total sunshine?

Recorded to nearest tenth of an hour

47

What is the daily mean wind direction and windspeed?

Knots, averaged over 24 hours
Directions given as bearings & compass directions
Mean windspeed also in Beaufort scale

48

What is a knot?

1 kn = 1.15 mph

49

What is the daily max gust?

Highest instantaneous wind speed recorded in knots

50

What is the daily max relative humidity?

% air saturation with water
Above 95% can be misty/foggy

51

What is daily mean cloud cover?

Measured in oktas - eighths of sky covered by cloud
Therefore max value is 8

52

What is daily mean visibility?

Greatest distance an object can be seen in daylight
Measured in decameters (Dm)

53

What is daily mean pressure measured in?

Hectopascals (hPa)