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