Chapter 1 - Data Collection

Question 1

Population

Answer 1

• all the items we are interested in

Question 2

Sample

Answer 2

• a subset of items chosen from a population

Question 3

Sampling frame

Answer 3

• when sampling units are of a population are individually named or numbered in a list

Question 4

Census testing

Answer 4

Adv - give completely accurate result
Disadv - time consuming, can’t be used when testing involves destruction, large volume of data

Question 5

Sample testing

Answer 5

Adv - less expensive, less time consuming, less data
Disadv - data may not be accurate, sample may not represent small sub groups of pop.

Question 6

Simple random sampling

Answer 6

1. firstly you need a sampling frame
2. assign each item a number from 1 to N
3. use a random no. generator to select ‘n’ unique numbers
4. choose the items corresponding to these numbers to form the sample

Question 7

Advantages of simple random sampling

Answer 7

• bias free
• easy and cheap to implement for small populations
• each sampling unit has an equal chance of being selected

Question 8

Disadvantages of simple random sampling

Answer 8

• not suitable for large population size
• sample may not accurately reflect population
• sampling frame is needed

Question 9

Systematic sampling

Answer 9

In systematic sampling the elements are chosen at regular intervals from an ordered list
1. you need a sampling frame
2. Assign each item a number from 1 to N
3. Starting at a random item between 1 and k, take every k^th element to form the sample
k = pop size/samp size

Question 10

Advantages of systematic sampling

Answer 10

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

Question 11

Disadvantages of systematic sampling

Answer 11

• can introduce bias if sampling frame is small and not random, as patterns can be picked up in the data
• a sampling frame is needed

Question 12

Stratified sampling

Answer 12

• Population divided into groups(strata) and a simple random sample is carried out in each group
  1. You need a sampling frame and a distinct strata, the same proportion n/N is sampled from each strata
  2. Within each strata, each item is assigned a different number and a random no. generator is used to select the number of unique numbers required.
  3. Choose the items corresponding to these numbers to form the sample

Question 13

Advantages of stratified sampling

Answer 13

• sample accurately reflects population structure
• guarantees proportional representation of groups within population

Question 14

Disadvantages of stratified sampling

Answer 14

• sampling frame is needed and population must be clearly classified into distinct stratas
• selection within each stratum suffers from same disadvantages as simple random sampling

Question 15

Quota Sampling

Answer 15

Population divided into groups according to characteristic
1. A quota of items/people in each group is set to try and reflect the group’s proportion in the whole population (quotas are calculated in the same way as stratified sampling)
2. Interviewer selects the actual sampling units until the quotas are reached
3. Once a quota is full, ignore subsequent sampling units that meet the characteristic

Question 16

Advantages and of quota sampling

Answer 16

• Allows a small sample to be still be representative of population
• No sampling frame required
• Relatively quick, easy and inexpensive

Question 17

Disadvantages of quota sampling

Answer 17

• non-random sampling can introduce bias
• population must be divided into groups which can be costly or inaccurate
• can depend on knowledge/expertise of researcher

Question 18

Opportunity sampling

Answer 18

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

Question 19

Advantages of opportunity sampling

Answer 19

• easy to carry out
• inexpensive

Question 20

Disadvantages of opportunity sampling

Answer 20

• Unlikely to provide a representative sample
• Highly dependant on individual researcher