C1 Data Collection

Question 1

Define a population

Answer 1

the whole set of items that are of interest

Question 2

Define a sample

Answer 2

some subset if the population intended to represent the population

Question 3

define a census

Answer 3

data collected from the entire population

Question 4

what are the advantages of using a census

Answer 4

should five completely accurate results

Question 5

what are the advantages of using a sample

Answer 5

• cheaper
• quicker
• less data to process

Question 6

what are the disadvantages of using a census

Answer 6

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

Question 7

what are the disadvantages of using a sample

Answer 7

• data may not be accurate

- data may not be large enough to represent small sub-groups

Question 8

how do you carry out SIMPLE RANDOM SAMPLING

Answer 8

• in sampling frame each item has an identifying number.

- use random number generator to select your sample

Question 9

what is SIMPLE RANDOM SAMPLING

Answer 9

• every sample has an equal chance of being selected

Question 10

advantages of SIMPLE RANDOM SAMPLING

Answer 10

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

Question 11

disadvantages of SIMPLE RANDOM SAMPLING

Answer 11

• not suitable when population size is large

- sampling frame needed

Question 12

what is SYSTEMATIC SAMPLING

Answer 12

• required elements are chosen at regular intervals in ordered list
  (start with a random number and take a sample from every eg. 5th)

Question 13

advantages of SYSTEMATIC SAMPLING

Answer 13

• simple and quick to use

- suitable for large samples/ populations

Question 14

disadvantages of SYSTEMATIC SAMPLING

Answer 14

• sampling frame needed

- can introduce bias if sampling frame not random

Question 15

what is STRATIFIED SAMPLING

Answer 15

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

Question 16

when is SYSTEMATIC SAMPLING used

Answer 16

• when sample is large and population naturally divides into groups

Question 17

advantages of SYSTEMATIC SAMPLING

Answer 17

• reflects population structure

- guarantees proportional representation of groups within population

Question 18

disadvantages of SYSTEMATIC SAMPLING

Answer 18

• population must be clearly classified into distinct strata

- selection within each stratum suffers the same disadvantages of random sampling

Question 19

what is QUOTA SAMPLING

Answer 19

• population is divided into groups according to characteristic
• A quota of items/people in each group is set to try and reflect the group’s proportion in the whole population
• (interviewer sets the sampling units)

Question 20

advantages of QUOTA SAMPLING

Answer 20

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

Question 21

disadvantages of QUOTA SAMPLING

Answer 21

• non-random smapling can introduce bias
• population must be divided into groups, which be costly or innacurate
• increasing scope of study increases number of groups, adding time/expense
• non-responses are not recorded

Question 22

what is OPPORTUNITY/CONVENIENCE SAMPLING

Answer 22

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

Question 23

advantages of OPPORTUNITY/CONVENIENCE SAMPLING

Answer 23

• easy to carry out

- inexpensive

Question 24

disadvantages of OPPORTUNITY/CONVENIENCE SAMPLING

Answer 24

• unlikely to provide a representative sample

- highly dependent on individual researcher