3.1 Sampling

Question 1

Population

Answer 1

The set of things you are interested in

Question 2

Sample

Answer 2

The subset of the population

Question 3

Parameter

Answer 3

The number that describes the entire population

Question 4

Statistic

Answer 4

A number taken from a single sample

Question 5

Census

Answer 5

Observes or measures every member of a population

It can be a survey/experiment

Question 6

Adv and Disadv of census

Answer 6

Adv
- give a completely accurate result

Disadv

• time consuming
• expensive
• hard to process large quantity of data

Question 7

Adv and disadv of sample

Answer 7

Adv

• less time consuming
• less expensive
• fewer people have to respond
• less data to process compared to census

Disadv

• data may not be accurate
• sample may not be large enough to give info about small sub-groups of the population

Question 8

Sampling unit

Answer 8

Individual units of a population

Question 9

Sampling frame

Answer 9

This is where sampling units of a population are individually named or numbered to form a list

Question 10

Different types of sampling

Answer 10

1. Simple random sampling
2. Systematic sampling
3. Stratified sampling
4. Opportunity sampling
5. Quota sampling
6. Cluster sampling

Question 11

Simple random sampling

Answer 11

Every member of the population is equally likely to be chosen. (A simple random sample of size n is one where every sample of size n has an equal chance of being selected)

Eg
Allocate each member in population a number and then use random numbers to choose a sample of desired size

Question 12

Systematic sampling

Answer 12

Find a sample of size n from a population of size N by taking one member from the first k members of the population at random and then selecting every kth member after that.

Question 13

Equation for systematic sampling

Answer 13

K = N/n

Question 14

Stratified sampling

Answer 14

When you know you want distinct groups to be represented in your sample, split the population into these distinct groups and then sample within each group in proportion to its size.

Question 15

Equation for stratified sampling

Answer 15

Question 16

Adv and disadv of simple random sampling

Answer 16

Adv

• free of bias
• easy and cheap to implement for small populations
• each sampling unit has a known and equal chance of selection

Disadv

• not suitable when the population/sample size is large
• a sampling frame is needed

Question 17

Adv and disadv of systematic sampling

Answer 17

Adv

• simple and quick to use
• suitable for large samples and large populations

Disadv

• a sampling frame is needed
• can introduce bias if the sampling frame is not random

Question 18

Adv and disadv of stratified sampling

Answer 18

Adv

• sample accuracy reflects the population structure
• guarantees proportional representation of groups within population

Disadv

• population must be clearly classified into distinct strata
• selection within each stratum suffers from the same disadvantages as simple random sampling

Question 19

Quota sampling

Answer 19

When you know you want distinct groups to be represented in your sample, decide how many members of each group you wish to sample in advance and use opportunity sampling until you have a large enough sample for each group.

Question 20

Opportunity sampling

Answer 20

Take samples from members of the population you have access to until you have a sample of the desired size.

Question 21

Cluster sampling

Answer 21

Split the population into clusters that you expect to be similar to each other, then take a sample from each of these clusters.

Question 22

Adv and disadv of quota sampling

Answer 22

Adv

• allows a small sample to still be representative of the pop
• no sampling frame required
• quick and easy and inexpensive
• allows for easy comparison between diff groups within a population

Disadvantage

• non-random sampling can introduce bias
• pop must be divided into groups, which can be costly/inaccurate
• non-responses are not recorded as such

Question 23

Adv and disadv of opportunity sampling

Answer 23

Adv

• easy to carry out
• inexpensive

Disadv

• unlikely to provide a representative sample
• highlight dependent on individual researcher

Question 24

Quantitative variable/data

Answer 24

Variables or data associated with numerical observations

Question 25

Qualitative variable/data

Answer 25

Variables or data associated with non-numerical observations

Question 26

Continuous variable/data

Answer 26

A variable/data that can take any value in a given range | Eg height

Question 27

Discrete variable/data

Answer 27

Variable/data that can only take specific values in a given range Eg feet size, blood group