sampling and data collection

Question 1

census

Answer 1

A census collects data about all the members of a population
For example: the Government in England does a national census every 10 years to collect data about every person living in England at the time

Question 2

advantage of a census

Answer 2

gives fully accurate results

Question 3

disadvantages of a census

Answer 3

It is time consuming and expensive to carry out
It can destroy or use up all the members of a population when they are consumables (imagine a company testing every single firework)

Question 4

advantages of sampling

Answer 4

It is quicker and cheaper than a census
It leads to less data needing to be analysed

Question 5

disadvantages of sampling

Answer 5

It might not represent the population accurately
It could introduce bias

Question 6

simple random sampling

Answer 6

if a sample of size is taken then every group of members from the population has an equal probability of being selected for the sample

Question 7

how is simple random sampling carried out

Answer 7

Simple random sampling is carried out by uniquely numbering every member of a population and randomly selecting begin math size 16px style n end style different numbers using a random number generator or a form of lottery (where numbers are selected randomly)

Question 8

systematic sampling

Answer 8

a sample is formed by choosing members of a population at regular intervals using a list

Question 9

A sample statistic

Answer 9

is a value computed using data from the sample
These are used to estimate population parameters
For example: the mean height of 200 16-year-olds from randomly selected cities in the UK

Question 10

how is systematic sampling carried out

Answer 10

To carry this out you would calculate the size of the interval

k= size of population/ size of the sample

and choose a starting point between 1 and then select every kth member after the first one

Question 11

Stratified sampling

Answer 11

the population is divided into disjoint groups (called strata) and then a random sample is taken from each group (stratum)

Question 12

how is stratified sampling carried out

Answer 12

The proportion of a stratum that is sampled is equal to the proportion of the population that belongs to that stratum

The number of members sampled from a stratum = size of sample/ size of population

The population could be split by age range, gender, etc

Question 13

quota sampling

Answer 13

the population is split into groups (like stratified sampling) and members of the population are selected until each quota is filled

Question 14

how is quota sampling carried out

Answer 14

If a member does not want to be included then another member is chosen instead
The members do not have to be selected randomly

Question 15

opportunity sampling

Answer 15

a sample is formed using available members of the population who fit the criteria

Question 16

when should simple random sampling be used

Answer 16

this should be used when you want a random sample to avoid bias

Useful when you have a small population or want a small sample (such as children in a class)

This can not be used if it is not possible to number or list all the members of the population (such as fish in a lake)

Question 17

when should systematic sampling be used

Answer 17

this should be used when you want a random sample from a large population

Useful when there is a natural order (such as a list of names or a conveyor belt of items)

In order for the sample to be random the sampling frame needs to be random

This can not be used if it is not possible to number or list all the members of the population (such as penguins in Antarctica)

Question 18

when should stratified sampling groups be used

Answer 18

this should be used when the population can be split into obvious groups of members (where members within a group have a common characteristic)

Useful when there are very different groups of members within a population

The sample will be representative of the population structure

The members selected from each stratum are chosen randomly

This can not be used if the population can not be split into groups or if the groups overlap

Question 19

when should quota sampling be used

Answer 19

this should be used when a small sample is needed to be representative of the population structure

Useful when collecting data by asking people who walk past you in a public place or when a sampling frame is not available

This can introduce bias as some members of the population might choose not to be included in the sample

Question 20

when should quota sampling be used

Answer 20

this should be used when a small sample is needed to be representative of the population structure

Useful when collecting data by asking people who walk past you in a public place or when a sampling frame is not available

This can introduce bias as some members of the population might choose not to be included in the sample

Question 21

what are the main criticisms of sampling techniques

Answer 21

Most sampling techniques can be improved by taking a larger sample

Sampling can introduce bias - so you want to minimise the bias within a sample

To minimise bias the sample should be random

A sample only gives information about those members

Different samples may lead to different conclusions about the population

Question 22

Qualitative data

Answer 22

Qualitative data is data that is usually given in words not numbers to describe something
For example: the colour of a teacher’s car

Question 23

Quantitative data

Answer 23

Quantitative data is data that is given using numbers which counts or measures something
For example: the number of pets that a student has

Question 24

Discrete data

Answer 24

Discrete data is quantitative data that needs to be counted
Discrete data can only take specific values from a set of (usually finite) values
For example: the number of times a coin is flipped until a tails is obtained

Question 25

continuous data

Answer 25

Continuous data is quantitative data that needs to be measured
Continuous data can take any value within a range of infinite values
For example: the height of a student

Question 26

how can age be discrete or continuous

Answer 26

If you mean how many years old a person is then this is discrete
If you mean how long a person has been alive then this is continuous

Question 27

population

Answer 27

refers to the whole set of things which you are interested in
For example: if a vet wanted to know how long a typical French bulldog slept for in a day then the population would be all the French bulldogs in the world

Question 28

sample

Answer 28

refers to a subset of the population which is used to collect data from
For example: the vet might take a sample of French bulldogs from different cities and record how long they sleep in a day

Question 29

sampling frame

Answer 29

a list of all members of the population
For example: a list of employees’ names within a company

Question 30

population parameter

Answer 30

a numerical value which describes a characteristic of the population
These are usually unknown
For example: the mean height of all 16-year-olds in the UK

Question 31

when should opportunity sampling be used

Answer 31

this should be used when a sample is needed quickly
Useful when a list of the population is not possible
This is unlikely to be representative of the population structure