Chapter 1: data collection

Question 1

What is population?

Answer 1

+ a group that we want to find information about

Question 2

What is a census?

Answer 2

+ when information about every member of the population is collected

Question 3

What is a sample survey?

Answer 3

+ when information is collected from a small representation of the population

Question 4

What is a sampling unit?

Answer 4

+ a person/object to be sampled
+ must be defined in such a way that any one
member of a population is not sampled more
than once

Question 5

What is a sampling frame?

Answer 5

+ the collection of all of the sampling units
+ ideally this should cover the whole population

Question 6

What are the advantages of the census?

Answer 6

+ representative of the population
+ lots of data

Question 7

What are the disadvantages of the census?

Answer 7

+ takes time
+ expensive
+ sort through a lot of data

Question 8

What are the advantages of a sample?

Answer 8

+ quicker and cheaper
+ less data to process

Question 9

What are the disadvantages of a sample?

Answer 9

+ maybe less representative of the population

Question 10

What is the method for simple random sampling?

Answer 10

1. give everyone a number between 1 and n (n= population size)
2. use a random number generator to select numbers between 1 and n and pick these people
3. ignore repeats
4. stop when the sample is full

Question 11

What are the advantages of simple random sampling?

Answer 11

+ free from bias
+ easy and cheap to implement for small populations and small samples

Question 12

What are the disadvantages of simple random sampling?

Answer 12

+ not suitable when the population size or the sample is large
+ a sampling frame is needed
+ sample may not be representative of groups within sample

Question 13

What is the method for systematic sampling?

Answer 13

1. give everyone in the population a number between 1 to N (N=pop size)
2. choose the first person to pick, using a random number generator, to get a number between 1 and k, where k=N/n
3. select every k’th person
4. stop once sample is full

Question 14

What are the advantages of systematic sampling?

Answer 14

+ simple and quick to use
+ suitable for a large samples and large populations

Question 15

What are disadvantages of systematic sampling?

Answer 15

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

Question 16

What is the method for stratified sampling?

Answer 16

1. split the people into different groups
2. decide the proportion of people to take from each group by doing (group size/pop size) x sample size
3. use simple random sampling to get this number from each group
4. if rounding needed, be careful to check that your total sample size is correct

Question 17

What are the advantages of stratified sampling?

Answer 17

+ allows you to have proportional representation of groups within a population
+sample should accurately reflect the population structure

Question 18

What are the disadvantages of stratified sampling?

Answer 18

+ only suitable if population can be grouped
+ selection within each group could have the same disadvantages as SRS

Question 19

What is the method for opportunity sampling?

Answer 19

1. approach people in the street to interview
2. stop once sample is full

Question 20

What are the advantages of opportunity sampling?

Answer 20

+ easy to carry out
+ cheap
+ no sampling frame required

Question 21

What are the disadvantages of opportunity sampling?

Answer 21

+ unlikely to provide representative sample
+ likely to create bias