Stats

Question 1

Define opportunity sampling

Answer 1

A sample is taken from the first n members of the population who are available and fit the criteria.

Question 2

Define a simple random sample.

Answer 2

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

Question 3

Define a census.

Answer 3

When you collect information from every member of a population.

Question 4

Advantages of a census.

Answer 4

• you get accurate information about pop, as every member has been surveyed
• true representation of population
• unbiased

Question 5

Disadvantages of a census.

Answer 5

• takes lots of time and effort for large pops
• expensive
• can be difficult to make sure all members are surveyed
• if tested items used up or damaged in some way, census is impractical

Question 6

Define sample units.

Answer 6

Individual members of the population

Question 7

Define sampling frame.

Answer 7

A full list of all the sampling units. Used to represent population when selecting random sample.

Question 8

Advantages of sampling.

Answer 8

• quicker and cheaper than census, and easier to get hold of required information
• only option when surveyed items are used up or damaged

Question 9

Disadvantages of sampling.

Answer 9

• variability between samples, each possible sample will give different results, so could just happen to select one which doesn’t accurately reflect pop
• samples can easily be affected by sampling bias.

Question 10

Advantage of simple random sampling.

Answer 10

• every member has equal chance of being selected, unbiased

Question 11

Disadvantage of simple random sampling.

Answer 11

• can be inconvenient if pop spread over large area

Question 12

Define systematic sampling.

Answer 12

Using a sampling frame, every nth member of the pop is sampled

Question 13

Advantage of systematic sampling.

Answer 13

• used for quality control, should give unbiased sample.

Question 14

Disadvantage of systematic sampling.

Answer 14

• regular interval could coincide with a pattern, which would make sample biased

Question 15

Advantage of opportunity sampling.

Answer 15

• data can be gathered quickly and easily.

Question 16

Disadvantage of opportunity sampling.

Answer 16

• isn’t random

- can be very biased, no attempt to obtain a representative sample.

Question 17

Define stratified sampling.

Answer 17

• divide pop into categories
• calculate total pop
• calculate number needed for each category: size of category in pop/ total size of pop x total sample size
• select sample for each category at random.

Question 18

Advantage of stratified sampling.

Answer 18

• guarantees proportional representation

Question 19

Disadvantage of stratified sample

Answer 19

• not useful when aren’t any obvious categories

- can be expensive

Question 20

Define quota sampling.

Answer 20

• divide pop into categories
• give each category a quota ( number of members to sample)
• collect data until quotas are met in all categories

Question 21

Advantage of quota sampling.

Answer 21

• can be done when isn’t full list of pop

- every sample member responds as interviewer continues until all quotas are met

Question 22

Disadvantage of quota sampling.

Answer 22

• easily biased by interviewer

Question 23

Define cluster sampling.

Answer 23

• divide pop into clusters covering whole pop, where no member of pop belongs to multiple clusters
• randomly select clusters to use in sample
• either use all members of selected clusters or randomly sample within each cluster to form sample

Question 24

Advantage of cluster sampling.

Answer 24

• more practical

- can incorporate other sampling methods at either stage, so quite adaptable

Question 25

Disadvantage of cluster sampling.

Answer 25

• results less representative of pop as whole as only sample certain clusters
• not always possible to separate pop into clusters in natural way

Question 26

Define null hypothesis.

Answer 26

Statement about the value of population parameter.

Question 27

Define alternative hypothesis.

Answer 27

A statement that describes the value of the population parameter if null hypothesis is rejected.

Question 28

Define test statistic.

Answer 28

A statistic calculated from sample data which is used to decide whether or not to reject the null hypothesis.

Question 29

Define critical region.

Answer 29

The set of all values of the test statistic that would cause you to reject the null hypothesis.

Question 30

How to calculate variance

Answer 30

Sum of (x- mean) ^2 / n

Question 31

Equation for probability of an event.

Answer 31

No. Of total outcomes where event happens/ total no. Of possible outcomes.

Question 32

What does p(A U B) =

Answer 32

P(A) + P(B) - P(A n B)

Question 33

Equation for P(A n B)

Answer 33

P(A) x P(B|A)

Question 34

What is true for independent events?

Answer 34

P(A n B) = P(A) x P(B)

Question 35

What a five conditions of binomial distribution?

Answer 35

• fixed number of trials
• trial results in either success or failure
• all trials independent
• probability of success is same in each trial
• variable is total number of successes in n trials

Question 36

What does Z equal

Answer 36

X- mean/ variance

Question 37

What are conditions for normal distribution

Answer 37

• data is continuous
• data is roughly symmetrically distributed with peak in middle
• data tails off either side of mean