Data Collection And Sampling Methods

Question 1

What is a population?

Answer 1

The whole set of items that are of interest.

Question 2

What does a census measure?

Answer 2

Every member of a population.

Question 3

What is a 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

What are the advantages of a census?

Answer 4

It should give a completely accurate result.

Question 5

What are the disadvantages of a census?

Answer 5

-time consuming and expensive.
-cannot be used when the testing process destroys the item
-hard to process large quantities of data

Question 6

What are the advantages of a sample?

Answer 6

-quicker and cheaper than a census
-fewer people need to respond
-less data to process than a census.

Question 7

What are the disadvantages of a sample?

Answer 7

-the data may not be as accurate
-the sample may not be large enough to give information about small subgroups of the population.

Question 8

What is are sampling units?

Answer 8

Individual units of a population.

Question 9

What is a sampling frame?

Answer 9

Sampling units are numbered to form a list.

Question 10

What is a parameter?

Answer 10

A number that describes the entire population.

Question 11

What is a statistic?

Answer 11

A number taken from a single sample.

Question 12

How does the size of a sample effect the validity of conclusions?

Answer 12

•Generally the larger the sample, the more accurate it is
•If the population is very varied you need a larger sample than if the population were uniform.
•Different samples can lead to different conclusions due to the natural variation in a population.

Question 13

What are the 6 types of sampling?

Answer 13

•simple random sampling
•systematic sampling
•stratified sampling
•quota sampling
•opportunity / convenience sampling
•cluster sampling (a sample from a sample)

Question 14

What is simple random sampling?

Answer 14

Every sample has an equal change of being selected.

Question 15

Method of simple random sampling?

Answer 15

-in a sampling frame each item is given an identifying number
-use a random number generator (on your calculator) to generate different random numbers.
-match numbers with corresponding sampling units.

Question 16

What are the advantages of simple random sampling?

Answer 16

•bias free
•easy and cheap implement
•each number has a known equal chance of being selected.

Question 17

What are the disadvantages of simple random sampling?

Answer 17

•not suitable when population size is large.
•sampling frame needed.

Question 18

What is systematic sampling?

Answer 18

Required elements are chosen at regular intervals in ordered list.

Question 19

Method of a systematic sampling?

Answer 19

•each item in given an identifying number
•find k by doing - population size ÷ sample size
• start at a random number between 1 and k take every kth element.

Question 20

What are the advantages of systematic sampling?

Answer 20

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

Question 21

What are the disadvantages of systematic sampling?

Answer 21

•sampling frame needed
•can introduce bias if sampling frame not random
•not random as not every item has an equal chance of being selected.

Question 22

What is satisfied sampling?

Answer 22

Population divided into groups (strata) and a simple random sample carried out in each group.

Question 23

What is a strata?

Answer 23

Groups that a population is divided into.

Question 24

Method of stratified sampling?

Answer 24

•allocate each sampling units in each group with a number.
•sample the same proportion from each strata. Using - (no. in strata ÷ no. in population) × sample size
• use a simple random sample to select the units from each strata.

Question 25

What are the advantages of stratified sampling?

Answer 25

•reflects population structure
•guarantees proportional representation of groups within a population
•has random selection within an individual group to reduce bias.

Question 26

What are the disadvantages of stratified sampling?

Answer 26

•population must be clearly classified into distinct stata.
•selection within each stratum suffers from same disadvantages as simple random sampling.
•(ie. sampling frame needed, not suitable for large samples)

Question 27

What are the 3 types of random sampling?

Answer 27

• simple random sampling
• systematic sampling
• stratified sampling

Question 28

What are the 3 types of non-random sampling?

Answer 28

• quota sampling
• opportunity / convenience sampling
• cluster sampling

Question 29

What is quota sampling?

Answer 29

Population divided into groups according to characteristic.

Question 30

Method of quota sampling.

Answer 30

A quota of items / people in each group is set to try and reflect the groups proportion in the whole population.
Interviewer selects the actual sampling units.
proportion isn’t always necessary

Question 31

What are the advantages of quota sampling?

Answer 31

-Allows small sample to still be representative of population.
-no sampling frame required
-quick,easy,inexpensive.
-allows for easy comparison between different groups in population.

Question 32

What are the disadvantages of quota sampling?

Answer 32

-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, adding time / expenses.
-non responses are not recorded.

Question 33

What is Opportunity / convenience sampling?

Answer 33

Sample take from people who are available at time of study, who meet criteria.

Question 34

Method of opportunity / convenience sampling.

Answer 34

Eg: take the first 20 people you meet outside a shop on a Monday morning who are carrying shopping bags.

Question 35

What are the advantages of opportunity / convenience sampling?

Answer 35

-easy to carry out
-inexpensive

Question 36

What are the disadvantages of opportunity / convenience sampling?

Answer 36

-unlikely to provide a representative sample.
-highly dependent on individual researcher

Question 37

What is cluster sampling?

Answer 37

Split the population into relevant groups. Choose a sample from these groups. From these samples chosen take a sample of the required size.

Question 38

What are the advantages of cluster sampling?

Answer 38

-easy to carry out
-inexpensive

Question 39

What are the disadvantages of cluster sampling?

Answer 39

-May not be representative of the population.
-non random sampling can introduce bias.