Chapter 1: Data Collection

Question 1

Population

Answer 1

the whole set of items that are of interest

Question 2

Census

Answer 2

observes or measures every member of a population

Question 3

Sample

Answer 3

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

Question 4

Sampling unit

Answer 4

individual units of a population that can be sampled

Question 5

Sampling frame

Answer 5

list of sampling units that have been individually named or numbered

Question 6

Census advantages

Answer 6

• Should give a completely, accurate result

Question 7

Census disadvantages

Answer 7

• Time consuming + expensive
• Can’t be used when testing process destroys item
• Hard to process large quantity of data

Question 8

Sample advantages

Answer 8

• Less time consuming and expensive than a census
• Fewer ppl. have to respond
• Less data to process than a census

Question 9

Sample disadvantages

Answer 9

• Data may not be as accurate

- Sample may not be large enough to give information about small sub-groups of the population

Question 10

What are the three types of random sampling?

Answer 10

• Simple random sampling
• Systematic sampling
• Stratified sampling

Question 11

Describe how to carry out simple random sampling

Answer 11

Sampling frame is needed. Each thing allocated a unique number and a selection of these numbers are chosen at random (either by RNG or ‘lottery sampling’)

Question 12

Advantages of simple random sampling

Answer 12

• Free of bias
• Easy + cheap to implement for small populations and small samples
• Each sampling unit has a known and equal chance of selection

Question 13

Disadvantages of simple random sampling

Answer 13

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

Question 14

Describe how to carry out systematic sampling

Answer 14

Required elements are chosen at regular intervals from an ordered list

e. g. sample size of 20 required from population of 100
- Take every fifth person since 100/20 = 5. Use a RNG to select a number between 1-5 for first person (e.g. if it was 2 - 2, 7, 12, 17…)

Question 15

Advantages of systematic sampling

Answer 15

• Simple + quick to use

- Suitable for large samples and large populations

Question 16

Disadvantages of systematic sampling

Answer 16

• Sampling frame needed

- Can introduce bias if sampling frame is not random

Question 17

Describe how to carry out stratified sampling

Answer 17

Population divided into mutually exclusive strata and random sample (by RNG) taken from each. Proportion of each strata sampled should be same.

number sampled in a stratum = (number in stratum/number in population) x overall sample size

Question 18

Advantages of stratified sampling

Answer 18

• Accurately reflects population structure

- Guarantees proportional representation of groups within a population

Question 19

Disadvantages of stratified sampling

Answer 19

• Population must be clearly classified into distinct strata

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

Question 20

What are the two types of non-random sampling?

Answer 20

Quota sampling and opportunity/convenience sampling

Question 21

Describe quota sampling

Answer 21

Divide the population into groups according to given characteristics (e.g. being left-handed) . The size of each group determines the proportion of the sample that should have that characteristic. The interviewer
should assess which group people fall into, as part of the interview. Once a quota has been filled,
no more people in that group are interviewed.

Question 22

Advantages of quota sampling

Answer 22

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

Question 23

Disadvantages of quota sampling

Answer 23

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

Question 24

Describe opportunity/convenience sampling

Answer 24

Consists of 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 (e.g. first 20 people you meet outside a supermarket on a Monday morning who are carrying shopping bags)

Question 25

Advantages of opportunity/convenience sampling

Answer 25

• Easy to carry out

- Inexpensive

Question 26

Disadvantages of opportunity/convenience sampling

Answer 26

• Unlikely to provide a representative sample

- Highly dependent on individual researcher

Question 27

What is quantitative data?

Answer 27

Data associated with numerical observations (e.g. shoe size)

Question 28

What is qualitative data?

Answer 28

Data associated with non-numerical observations (e.g. hair colour)

Question 29

What is continuous data?

Answer 29

Data that can take any value in a given range (e.g. time (2s, 2.1s, 2.01s)

Question 30

What is discrete data?

Answer 30

Data that can only take specific values (e.g. number of girls in a family (because you can’t have 2.65 girls in a family)

Question 31

In a grouped frequency table, what do class boundaries tell you?

Answer 31

Maximum and minimum values that belong in each class

Question 32

In a grouped frequency table, what is the midpoint?

Answer 32

Average of the class boundaries

Question 33

In a grouped frequency table, what is the class width?

Answer 33

Difference between upper and lower class boundaries

Question 34

What do you have to be careful about for continuous data in a grouped frequency table?

Answer 34

Data values have been rounded to nearest mm so (e.g. class boundaries would be 29.5 to 31.5 instead of 30-31)