sampling

Question 1

what is a population?

Answer 1

the whole set of items that are of interest

Question 2

what is a sample?

Answer 2

some subset of the population intended to represent the population

Question 3

what is a sampling unit?

Answer 3

each individual thing in the population that can be sampled

Question 4

what is a sampling frame?

Answer 4

when sampling units of a population are individually named or numbered to form a list

Question 5

what is a census?

Answer 5

data collected from the entire population

Question 6

what are the advantages of a cesus?

Answer 6

should give completely accurate result

Question 7

what are the disadvantages of a census?

Answer 7

-time consuming and expensive
-can not be used when testing involves destruction
-large volume of data to process

Question 8

what are the advantages of a smaple?

Answer 8

-cheaper
-quicker
-less data to process

Question 9

what are the disadvantages of a sample?

Answer 9

-data may not be accurate
-data may not be large enough to represent small subgroups

Question 10

what is a sampling error?

Answer 10

the difference between the actual value of the parameter and the value derived from a sample

Question 11

what are parameters?

Answer 11

a calculation of a sample or population

Question 12

what is bias?

Answer 12

a systematic error in the collection of the sample

Question 13

what can lead to a biased sample?

Answer 13

-sample is not representative of the population
-leading questions
-the wrong person asking questions
-small sample size

Question 14

what are the two types of sampling?

Answer 14

random and non-random

Question 15

what is random sampling?

Answer 15

every item or person has an equal chance of being selected for the sample

Question 16

what is non-random sampling?

Answer 16

sample selection is based on other factors than just random chance

Question 17

what is simple random sampling?

Answer 17

every sample has an equal chance of being selected

Question 18

how to carry out simple random sampling?

Answer 18

in a sampling frame, each item has an identifying number. use a random number generator to pick the sample

Question 19

what are the advantages of simple random sampling?

Answer 19

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

Question 20

what are the disadvantages of simple random sampling?

Answer 20

-not suitable when the population size is large
-sampling frame needed

Question 21

what is systematic sampling?

Answer 21

required elements are chosen at regular intervals in ordered list
take every kth element
where k=
pop size/ samp size
starting at random item between 1 and k

Question 22

what are the advantages of systematic sampling?

Answer 22

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

Question 23

what are the disadvantages of systematic sampling?

Answer 23

-sampling frame needed
-can introduce bias is sampling frame is not random

Question 24

what is stratified sampling?

Answer 24

-population divided into groups and a simple random sample carried out in each group
-same proportion samp size/pop size sampled from each strata

Question 25

when is stratified sampling used?

Answer 25

when sample is large and population naturally divides into groups

Question 26

what are the advantages of stratified sampling?

Answer 26

-reflects population structure
-guarantees proportional representation of groups within population

Question 27

what are the disadvantages of stratified sampling?

Answer 27

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

Question 28

what is opportunity/convenience sampling?

Answer 28

sample taken from people who are available at time of study who meet criteria

Question 29

what are the advantages of opportunity/convenience sampling?

Answer 29

-easy to carry out
-inexpensive

Question 30

what are the disadvantages of opportunity/convenience sampling?

Answer 30

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

Question 31

what is cluster sampling?

Answer 31

non-random stratified sampling

Question 32

how to carry out cluster sampling?

Answer 32

-define each cluster (should be representative of population)
-collect random samples from each cluster

Question 33

what are the advantages of cluster sampling?

Answer 33

-no sampling frame
-inexpensive
-choosing clusters instead of evaluating entire population

Question 34

what are the disadvantages of cluster sampling?

Answer 34

unlikely to provide a representative sample because clusters tend to have similar characteristics resulting in overrepresentation within a cluster

Question 35

what is quota sampling?

Answer 35

-population divided into groups according to characteristics
-a quota of items/people in each group is set to try and reflect the group’s proportion in the whole population
-interviewer selects the actual sampling units

Question 36

what are the advantages of quota sampling?

Answer 36

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

Question 37

what are the disadvantages of quota sampling?

Answer 37

-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 and expense
-non-responses are not recorded

Question 38

what is the difference between cluster and quota?

Answer 38

in cluster you use simple random sampling in the groups, in quota you advertise and get volunteers until the ‘quota’ for each group is filled