S3 Sampling

Front 1

Define a population.

Back 1

The whole set of items that are of interest.

Front 2

Define raw data.

Back 2

The information obtrained from a census or sample survey.

Front 3

Define a census.

Back 3

Observes or measures every item in a population.

Front 4

When would a census be used?

Back 4

When the population is very small or extreme accuracy is required.

Front 5

Define a sample (survey).

Back 5

A selection of observations taken from a sub-set of the population. Used to find out information about the population as a whole.

Front 6

What are the advantages of a census (1)?

Back 6

It should give a completely accurate result.

Front 7

What are the disadvantages of a census (4)?

Back 7

Expensive, time consuming, information is difficult to process as there is so much of it, cannot be used to test to destruction.

Front 8

What are the advantages of a sample survey (4)?

Back 8

Results are obtained quicker than a census, costs less than a census, fewer people have to respond in the sample, there is less data to deal with than in a census.

Front 9

What are the disadvantages of a sample survey (2)?

Back 9

The data may not be as accurate, the sample may not be large enough to give information about small sub-sets of the population.

Front 10

Define random sampling.

Back 10

Each unit is chosen entirely by chance and each member of the population has a known chance of being included in the sample.

Front 11

Define simple random sampling (3).

Back 11

A sampe of size n is a simple random sample if every other sample of size n has an equal chance of being selected.

It is sampling without replacement.

A sampling frame is required.

Front 12

Define a sampling frame.

Back 12

A list identinfting every sample unit which could be included in the sample.

Front 13

What are the advantages of simple random sampling (4)?

Back 13

(provided that the population is small) it is cheap, simple, standard formulae can be used to analyse the results, each person/unit is included only once.

Front 14

What are the disadvantages of simple random sampling (2)?

Back 14

It is not suitable when the population is large, a sampling frame is required.

Front 15

What are two simple techniques for simple random sampling?

Back 15

Random number sampling and lottery/ticket sampling.

Front 16

What are the advantages of random number sampling (3)?

Back 16

The numbers are truly random and free from bias, easy to use, each number has a known and equal chance of being selected.

Front 17

What is the disadvantage of random number sampling?

Back 17

Not suitable for large populations.

Front 18

What are the advantages of lottery sampling (3)?

Back 18

Tickets are drawn at random, easy to use, each ticket has a known chance of selection.

Front 19

What are the disadvantages of lottery sampling (2)?

Back 19

Not suitable where the population is large, a sampling frame is needed.

Front 20

Definine systematic sampling.

Back 20

The required elements are chosen at regular intervals from an ordered list. Select first unit randomly.

Front 21

How do you calculate a systematic sample?

Back 21

Take every kth element from a sampling frame where k=N/n N=population size and n=sample size.

Front 22

When is systematic sampling used?

Back 22

When the population is too large for simple random number sampling.

Front 23

What are the advantages of systematic sampling?

Back 23

It is simple to use and suitable for large samples.

Front 24

What are the disadvantages of systematic sampling?

Back 24

It is only random if the ordered list is truly random and it can introduce bias.

Front 25

What is stratified sampling?

Back 25

A form of random sampling in which the population is divided into mutually exclusive groups (strata) and a random sample is taken from each. The same proportion of each stratum is taken in the sample as is found in the population.

Front 26

How do you calculate the number sampled in a stratum?

Back 26

the number in the stratum divided by the size of the population multiplied by the overall sample size.

Front 27

What are the advantages of stratified sampling (2)?

Back 27

It can give more accurate estimates than simple random sampling where there are clear strata present. It reflects the population structure.

Front 28

What are the disadvantages of stratified sampling (2)?

Back 28

Within the strata, the problems are the same as for any simple random sample. If the strata are not clearly defined they may overlap.

Front 29

When is non-random sampling used?

Back 29

When it is not possible to use random methods, for example when no sampling frame is available.

Front 30

Explain quota sampling.

Back 30

The population is divided up into groups in terms of gender, social class etc. The number of people in each group is set to try and reflect the group's proportion in the whole population. The interviewer selects the actual sampling units.

Front 31

What are the advantages of quota sampling (3)?

Back 31

It enables the fieldwork to be done quickly because a representative sample can be achieved with a small sample size.

Costs are kept to a minimum.

Administering the test is easy.

Front 32

What are the disadvantages of quota sampling (4)?

Back 32

It is not possible to estimate the sampling errors as it is not a random process.

The interviewer has to choose the respondants and may not be able to judge the characteristics easily.

Non-responses are not recorded.

It can introduce interviewer bias in who is included.

Front 33

What is primary data?

Back 33

Data which is collected by or on behalf of the person who is going to use it.

Front 34

What is secondary data?

Back 34

Data which is neither collected by nor on behalf of the person who is going to use it.

Front 35

What are the advantages of primary data (3)?

Back 35

The collection method is known.

The accuracy is known.

The exact data needed are collected.

Front 36

What are the disadvantages of primary data (1)?

Back 36

It is costly in time and effort.

Front 37

What are the advantages of secondary data (3)?

Back 37

They are cheap to obtain (government publications for example).

A large quantity of information is available on the internet.

Much of the data has been collected for years and can be used to plot trends.

Front 38

What are the disadvantages of secondary data (2)?

Back 38

Bias is not always recognised.

It can be in a form that is not easy to deal with.