Data Collection

Question 1

What is probability theory?

Answer 1

The study of the mathematical rules that govern random events.

Question 2

What is an event?

Answer 2

A possible outcome of an experiment or observation.

Question 3

What is descriptive statistics?

Answer 3

The use of statstics to summarise a set of known data in a clear and consise way.

Question 4

What is statstical inference?

Answer 4

The methods and practice of forming judgements about the parameters of a population, usually on the basis of random sampling.

Question 5

What is statistics used for?

Answer 5

• designing experiments and other data collection
• summarising info to aid understanding
• drawing conclusions from data
• estimating the present or predicting the future

Question 6

What are the general steps used in stats?

Answer 6

1. pose a question, what are the objectives of the study?
2. decide what to measure and how to measure it
3. collect or generate data
4. explore data, check for oddities
5. calculate formal statistical summaries and carry out tests to answer posed question
6. explore sensitivity of analysis to assumptions
7. communicate findings

Question 7

What are the three general methods for collecting or generating data?

Answer 7

• polls and surveys
• experiments
• observational studies

Question 8

What is a target population?

Answer 8

A collection of objects/individuals we want to learn something about.

Question 9

What is a sample?

Answer 9

A subset of the target population.

Question 10

What is a census?

Answer 10

When information from the whole target population is obtained.

Question 11

What is a poll or survey?

Answer 11

The process of collecting data from a sample in order to obtain info about the whole population.

Question 12

What are the cons of censuses?

Answer 12

• difficult to make sure everyone participates
• more expensive than surveys
• takes longer
• more practical to take survey

Question 13

What is a sampling error?

Answer 13

A single random sample will not give an exact “right answer”; it is unavoidable without taking a census.

Question 14

How do we choose a sample?

Answer 14

• each member of the population has an equal chance of being chosen
• avoids bias
• allows for the calculation of the likely size of sampling errors

Question 15

What is a variable?

Answer 15

Some characteristic of each individual in the population.

Question 16

What is a parameter?

Answer 16

A numerical summary of a variable for a population.

Question 17

What is a statistic?

Answer 17

A numerical summary of a variable for the sample.

Question 18

What is precision?

Answer 18

The value of the statistic is similar in all samples.

Question 19

What is a bias?

Answer 19

It implies that the sample statistic tends to differ from the population parameter in a consistant way (there is a systematic error).

Question 20

Describe two simple sampling strategies.

Answer 20

1. number every member of the population, draw numbers from a hat
2. calculate a fixed periodic interval:
   k = N/n
   where k is the inverval between successive samples, n is the sample size and N is the population size
   pick a random value between 1 and k (call this q)
   sample the qth individual, then the (q + k)th, then the (q + 2k)th, etc

Question 21

What are the benefits of systematic sampling over random sampling?

Answer 21

• easier; only one random number has to be drawn

- BUT if population contains some periodic variation which lines up with k, sample will be biased

Question 22

What is stratified sampling?

Answer 22

The population is divided into different categories (or strata) and different samples are taken from each stratum.

Question 23

What is selection bias?

Answer 23

Introduced when the selected sample is not representive of the population of interest.

Question 24

What is self-selection bias?

Answer 24

Occurs when people decided whether they wish to participate in the survey or not.

Question 25

What is interviewer effects?

Answer 25

Different interviewers asking the same question can obtain different results.

Question 26

What is non-response bias?

Answer 26

When target population don't respond and non-respondents tend to behave differently to repondents.

Question 27

What is question effects?

Answer 27

Subtle variation in question wording can have an effect on the responses.

Question 28

What is survey format? (As a reason for bias)

Answer 28

Results may be affected by factors such as question order or if the survey is conducted by mail, by phone or in person.

Question 29

What are behavioural considerations?

Answer 29

People tend to answer questions in a way they consider to be socially acceptable.

Question 30

What does transferring findings mean?

Answer 30

When results from one population are transferred to another.

Question 31

What is an experiment?

Answer 31

Used to try and discover whether a "treatment" or "condition" has an effect on individuals.

Question 32

What is a randomised experiment?

Answer 32

Treatments are randomly allocated to experimental units.

Question 33

What are subjects?

Answer 33

Experimental units that are human.

Question 34

What does partitioned mean? (Or, what are blocked experiments)

Answer 34

Individuals are assigned to groups (eg male/female), this reduces natural variability.

Question 35

What is a placebo?

Answer 35

A drug with no known effects.

Question 36

What is double blinding?

Answer 36

When the doctor doesn't know which treatment they are offering, neither does the patient, stops doctors having differences in behaviour.

Question 37

What is a control group?

Answer 37

A group of units not given any form of treatment.

Question 38

How many times should experiments be repeated?

Answer 38

At least twice the number of treatments.

Question 39

What is an observational study?

Answer 39

No treatment given to subjects, instead naturally occuring events are recorded, used sometimes when its difficult to carry out a randomised experiment.

Question 40

What are the two types of observational study?

Answer 40

- prospective (looking forward, choose samples now and follow up in the future) - retrospective (looking backward, choose samples and examine previous data) special case (case-control): seperate samples into cases and controls, look back and compare histories

Question 41

Can observational studies provide conclusive evidence for causation? What about a randomised experiment?

Answer 41

obs study - no | exp - possible to argue causation

Question 42

What is a confounding variable?

Answer 42

Some factor that's not accounted for, introduces a difference in treatment groups, NOT due to treatment.

Question 43

Name two types of sampling for an area (of land for example).

Answer 43

- plot sampling (completely random or systematic grid (which in turn can be random or systematic)) - strip sampling (simple random or systematic sampling with random start)

Question 44

What is a response variable?

Answer 44

Variable/info we would like to describe or predict.

Question 45

What is an explanatory variable?

Answer 45

Covariates/info we expect might help us explain or predict the response variable.