Sampling

Question 1

what is a census

Answer 1

measures or observes every member of a population

Question 2

what is a sample

Answer 2

is a selection of observations taken from a subset of population and used to find out more information about the population as a whole

Question 3

what is the advantage of taking a census

Answer 3

results should be completely accurate

Question 4

what are the disadvantages of taking a census

Answer 4

• time consuming and can be expensive
• cannot be used when test as it destroys the process
• hard to process a large quantity of data

Question 5

what are the advantages of a sample

Answer 5

• less time consuming and cheaper
• fewer people have to respond
• less data needs to be processed

Question 6

what are the disadvantages of a sample

Answer 6

• data may not be as accurate
• sample may not be large enough to give information about small subgroups of the population

Question 7

what are sample units

Answer 7

individual units of a population

Question 8

what’s a sampling frame

Answer 8

a list which contains sampling units which have been named and numbered

Question 9

what are the three types of random sampling

Answer 9

simple random
systematic
stratified

Question 10

what is simple random sampling

Answer 10

a simple random sample of size n is one where every sample of size n has an equal chance of being selected

Question 11

explain how a simple random sample can be taken using a calculator or random number generator

Answer 11

• number each thing from 1-N.
• use a calculator or random number generator to generate 12 random numbers between 1-N
• select the members who correspond to the numbers

Question 12

explain how a simple random sample can be taken using lottery sampling

Answer 12

write the names of the things on identical cards and place them in a hat. draw a certain number of cards and select these numbers

Question 13

what are the advantages of simple random sampling

Answer 13

• free of bias
• easy and cheap for small samples and populations
• each sampling unit has a known and equal chance of selection

Question 14

what are the disadvantages of simple random sampling

Answer 14

• not suitable for large samples and populations
• sampling frame needed

Question 15

what is systematic sampling

Answer 15

the required elements are chosen at regular intervals from an ordered list

Question 16

what are the advantages of systematic sampling

Answer 16

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

Question 17

what are the disadvantages of systematic sampling

Answer 17

• a sampling frame is needed
• bias introduced is sampling frame is not random

Question 18

what is stratified sampling

Answer 18

the population is divided into mutually exclusive strata and random sample is taken from each

Question 19

what is the equation for a number sampled in a stratum

Answer 19

(number in stratum/number in population) x overall sample size

Question 20

explain how you can use stratified sampling

Answer 20

• take the total number
• find the number of the thing needed from each group (if the umber of workers required is not a whole number, it is rounded off to the nearest whole number)
• number the things from 1-N
• use a random number generator or table to produce the required quantity of random numbers

Question 21

what are the advantages of stratified sampling

Answer 21

• sample accurately reflects population structure
• proportional representation of group within population

Question 22

what are the disadvantages of stratified sampling

Answer 22

• population must be clearly classified into distinct strata
• same disadvantages as simple random sampling within each stratum

Question 23

what are the two types of non random sampling

Answer 23

quota
opportunity

Question 24

what is quota sampling

Answer 24

an interviewer or researcher selects a sample that reflects the characteristics of the whole population

Question 25

what are the advantages of quota sampling

Answer 25

• allows a small sample to still be representative of the population
• no sampling frame required
• quick, easy and inexpensive
• easy comparison between different groups within a population

Question 26

what are the disadvantages of quota sampling

Answer 26

• 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, which adds time and expenses
• non-responses not recorded

Question 27

what is opportunity (convenience) sampling

Answer 27

sample is taken from people who are available at the time of study and who fits the criteria you are looking for

Question 28

what is the advantage of opportunity sampling

Answer 28

its easy and inexpensive

Question 29

what are the disadvantages of opportunity sampling

Answer 29

• unlikely to provide representative results
  -highly dependent on individual researcher

Question 30

what is quantitative data

Answer 30

variables or data associated with numerical observations

Question 31

what is qualitative data

Answer 31

variables or data associated with non numerical observations

Question 32

in which variable can a variable take any value and which can it only take specific values

Answer 32

any given value is a continuous variable
can only specific values is discrete data

Question 33

in a grouped frequency table what specific data values are NOT shown

Answer 33

• class boundaries shows the max and min values of each group or class
• the midpoint is the average of the class boundaries
• the class width is the difference between upper and lower class boundaries