Statistics

Question 1

Define simple random sampling and its advantages and disadvantages

Answer 1

• a simple random sample of size n is one where every sample of size n has an equal chance of being selected
  + unbiased, easy & cheap
  ~ unsuitable for large samples/populations, sampling frame needed

Question 2

Describe systematic sampling and its advantages and disadvantages

Answer 2

• required elements are chosen at regular intervals from an ordered list
• pop/sample size=nth
  + simple & quick, suitable for large pop/sample
  ~ sampling frame needed, bias if sampling frame is not random

Question 3

Describe stratified sampling and its advantages and disadvantages

Answer 3

• population is divided into mutually exclusive strata and a random sample is taken from each (proportional)
  -sub group/ pop x sample size, number each group and randomly generate sample of each group
  + accurately reflects pop structure, proportional representation
  ~ pop size must be clearly classified into distinct strata, simple random for each group

Question 4

Describe quota sampling and its advantages and disadvantages

Answer 4

• interviewer selects a sample that reflects characteristic of the whole pop
  + representative, no sampling frame, quick & easy & cheap, easy comparison between groups within a pop
• non random bias, inaccurate group classification, non responses not recorded

Question 5

Describe opportunity sampling and its advantages and disadvantages

Answer 5

• sample taken from people available at the time and that fit the criteria looked for
  + easy and inexpensive
  ~ unlikely to be representative of pop, highly dependant individual researcher

Question 6

Frequency density=

Answer 6

frequency / class width

Question 7

Equation for linear interpolation

Answer 7

• table with fed and cow
• lower of the range + (how many into range / frequency) = median/LQ/UQ