Estimation

Question 1

What is a confidence interval?

Answer 1

A range of values centred on the sample estimate which is likely to include the population parameter with a given probability. Usually 95%

Question 2

Why are confidence intervals used?

Answer 2

To give a range of plausible values for the effect of an intervention on an outcome

Question 3

What is a population?

Answer 3

Any collection of individuals (or measurements made) in which we are interested in

Question 4

What is population distribution?

Answer 4

The frequency distribution of a variable in the population

Question 5

Give examples of population parameters

Answer 5

Means
Medians
Standard deviations
Proportions

Question 6

What is a sample?

Answer 6

Any subset of a population, ideally selected to be representative

Question 7

What are the two types of sampling methods?

Answer 7

Probability and non-probability

Question 8

What is probability sampling?

Answer 8

Each member of the population has a known probability of being selected

Question 9

Give examples of probability sampling

Answer 9

Random
Systematic
Stratified
Cluster
Multistage

Question 10

What is non-probability sampling?

Answer 10

Members are selected from the population in a non-random manner

Question 11

Give examples of non-probability sampling

Answer 11

Convenience
Self-selecting
Judgement
Quota

Question 12

What are sample statistics

Answer 12

Summary values calculated in samples
E.G Means and proportions

Question 13

What is accuracy?

Answer 13

The absence of bias
If samples we repeatedly drawn and the means drawn, the sample mean should be centred about the population mean

Question 14

What is precision?

Answer 14

Repeatability
If samples we repeatedly drawn and the means calculated, these sample means should show little variation. The answers should be closer together

Question 15

What is the sampling distribution of a statistic?

Answer 15

The frequency of distribution of that statistic over all possible samples of a given size selected from the population

Question 16

What is standard error?

Answer 16

The standard deviation of the sampling distribution of a statistic

Question 17

How do you calculate confidence intervals?

Answer 17

Estimate +/- M x standard error of estimate

Question 18

What multiplier do you use when calculation 95% confidence intervals? And why?

Answer 18

1.96
Because 95% of a normal distribution lies within 1.96 standard deviations of the mean

Question 19

What is defined as a large sample?

Answer 19

A sample larger than 30
n >30

Question 20

How do you calculate the standard error of a sample mean?

Answer 20

SE(x bar) = s / sqr rt n

Question 21

How do you calculate the 95% confidence interval for a population proportion (pie)?
When n is large

Answer 21

P +/- 1.96 (sqr rt) (P(P-1) / n)

Question 22

What is the definition of 95% confidence intervals?

Answer 22

In 95% of repeated samples from the population, confidence intervals calculated this way will capture the population parameter

Question 23

What is classified as a small sample?

Answer 23

Less than 30 people
n<30

Question 24

What are the two changes made when calculating confidence intervals when using a small sample?

Answer 24

Assume that the variable of interest is normally distributed in the population from which the sample came.

No longer use normal distribution to obtain the multiplier, instead the multiplier comes from the students t distribution ( shape depends on degrees of freedom)

Question 25

What is the equation for working out the 95% confidence intervals when using a small sample size?

Answer 25

(X bar) +/- (t, (n-1, 0.025) s/ sqr rt n)