Data Collection

Question 1

What’s a population

Answer 1

Entire collection of things you’re investigating.

Question 2

Size of population

Answer 2

N

Question 3

Mieuw symbol

Answer 3

Mean of population

Question 4

Looks like 6 squared symbol.

Answer 4

Variance of population

Question 5

Census

Answer 5

Survey of all members of population

Question 6

Advantages of census

Answer 6

Accurate because all members considered

Unbiased

No worries about sampling frames or representative samples

Question 7

Disadvantages of census

Answer 7

Long costly

Cant test to destruction

Difficult to make sure all pop surveyed and done accurately?

Difficult to process large data sets may not be relevant.

Question 8

What’s a sample

Answer 8

Selection subset of population

Question 9

Size of sample

Answer 9

n

Question 10

Sample mean

Answer 10

X with bar on top

Question 11

Variance of sample denoted

Answer 11

S squared

Question 12

Sample unit

Answer 12

Single item of population

Question 13

Sampling frame

Answer 13

List database of all members of population

Question 14

Sample survey

Answer 14

Investigation collects data From every member of sample.

Well conducted survey can provide very good estimates.

Question 15

Advantages of sampling

Answer 15

Large well mixed sample can represent pop

Cheaper and quicker than census

Can test products to destruction

Data readily available can be more detailed and better quality

Question 16

Disadvantages of sampling

Answer 16

Can be biased because of poorly designed sample methods.

Can be inaccurate because of random variations.

Sample size may not give information about sub groups of pop.

There may be no sampling frame.

Question 17

Sampling error

Answer 17

Error due to a sample survey there are two of those

Question 18

Sampling error

Random error

Answer 18

Error caused by random variations. These errors can be positive or neg, on average size of random errors is zero.

Question 19

Sampling error

Bias or systematic error

Answer 19

Error caused by non random method of choosing sample. These errors can be positive or neg, on average this error is non zero (biased)

Question 20

Random sampling

Answer 20

Each item chosen by pure chance.

Free from bias, sampling frame required, difficult more expensive than non random samples.

Question 21

Three types of random samples

Answer 21

Simple random sampling

Stratified sampling

Systematic sampling

Question 22

Simple random sampling

Answer 22

Sample of size n that has equal chance of being selected as any other sample of size n.

Question 23

Stratified sampling

Answer 23

Population of size N divided into mutually exclusive subgroups called strata.

Strata can be decided by one or more criteria.

Random sample taken from each stratum. Total sample size is n.

Question 24

Sample size for each stratum =

Answer 24

Population of each stratum x n/N

Question 25

Stratified sampling advantage and disadvantage

Answer 25

Good with diverse populations Can be difficult to identify meaningful strata

Question 26

Systematic sampling

Answer 26

Elements chosen at regular intervals from an ordered list. First term is chosen from 1 to k. To introduce some randomness. k=N/n. And every kth element thereafter is chosen from ordered list. Only random is ordered list is truly random.

Question 27

Different methods of picking random samples

Answer 27

Random number sampling Lottery sampling With replacement Without replacement

Question 28

Random number sampling

Answer 28

Every member of sampling frame is allocated a number. Random numbers are created (table generator) elements chosen if their numbers come up.

Question 29

Lottery sampling

Answer 29

Every member of sampling frame is allocated a ticket or ball which is identified by number or name. Tickets drawn one at a time. Difficult to do with large numbers.

Question 30

With replacement

Answer 30

A chosen item is replaced, so can appear more than once in a sample.

Question 31

Without replacement

Answer 31

A chosen item is not replaced, so can appear only once in a sample.

Question 32

Non random samples

Answer 32

Quota sampling Opportunity sampling

Question 33

Advantages and disadvantages of non random samples

Answer 33

Cheaper, quicker, convenient as dont require sampling frame. Introduce bias.

Question 34

Quota sampling

Answer 34

Alternative to stratified sampling. Strata sampled in non random way. An interview has a quota (a set number) of people to interview from different groups (strata). The interviewer selects individuals and once the quota reached no more interviews in that group. Convenient and cheap but biased. Commonly used in street/market research.

Question 35

Opportunity sampling

Answer 35

Uses people from target population available at the time and willing to take part. Selecting a sample of students from those leaving a library. Convenient but biased.