Statistics

Question 1

Difference between incidences and prevalence?

Answer 1

Incidence - Rate new cases arising

Prevalence - N of cases at time of counting

Question 2

Difference risk and odd

Answer 2

Think tossing a coin

Risk: 1/2 = 0.5

Odds: 1/1 = 1 Number time event occurs

Question 3

What type of studies used to calculate risk ratio/relative risk

Answer 3

Large cohort study. Large population set with exposed and non exposed group. Compare number of outcomes in each group.

Question 4

Using table show how you calculaterisk ratio/relative risk

Answer 4

Question 5

What types of studies are used to calculate odds ratio?

Answer 5

Retrospective or case-control studies
Smaller data set

Question 6

Using table explain how odds ratio calculated

Answer 6

Question 7

For either RR or OR what is the meaning
1
>1
<1

Answer 7

1 = No difference
>1 = Exposure likely risk factor
< 1 = Exposure likely protective

Question 8

If the CI crosses which numerical value does that mean there is no statistic significance for
1) risk and odds ratios
2) means/percetnage/medians

Answer 8

1) 1
2) 0

Question 9

Draw a table to explain type 1, type 2 errors

Answer 9

Question 10

How to increase the power of a study>

Answer 10

The power of a study increases as the chances of commingling a Type 2 error decreases
1-beta
Power usually set to 80%, accepting 20% of the time we will miss a real difference

Question 11

Flow chart to work out statistical test

Answer 11

Question 12

What is the ability of a test to detect disease?

Answer 12

Sensitivity

TP/TP+FN

Question 13

What is the ability of a test to exclude the presence of a disease when it is not truly present?

Answer 13

Specificity
TN/TN+FP

Question 14

Which test – the probability that an individual with the +ve test has or will develop the disease

Answer 14

PPV

TP/TP+FP

Question 15

which test - the probability that a subject with a negative test result actually does not have the disease

Answer 15

NPP

TN/TN+FN

Question 16

Table showing calculations sensitivity, specificity,postive predictive value and negative predictive value

Answer 16

Question 17

What is the positive likelihood ration

Answer 17

sensitivity/(1-specificity)

Question 18

What is the negative likelihood ration

Answer 18

specificity/(1-sensitivity)

Question 19

How doe likelihood ratios impact post-test probability of disease?

Answer 19

Question 20

How to calculate perinatal mortality rate?

Answer 20

Total number of deaths fetal deaths from 20 weeks/livebirth + stillbirth in 1 year x 1,000

Question 21

How to calculated neonatal mortality rate?

Answer 21

N of children doing <28days/liver births in a year x 1000

Question 22

Post-neonatal death

Answer 22

After 28 days but before 1 year

Question 23

How to calculate infant mortality rate?

Answer 23

Number of newborns dying < 1 year/number of live births x1,000

Question 24

What is needed to calculate sample size?

Answer 24

1. Current response rate
2. Estimated difference in response rates
3. 1 or 2 tailed
4. p-value
5. power

Question 25

What is standard deviation?

Answer 25

Square root of the variance
Most common measure of spread

Question 26

How to calculate varience

Answer 26

Question 27

In standard deviation, what % is 1,2 and 3 SD from the mean?

Answer 27

1 68%
2 95%
3 99.7%

Question 28

What is a Z score

Answer 28

Is measured in terms of standard deviations from the mean.
0 = identical to mean

Can be used in Z score table to work out %

Question 29

How to calculate standard error?

Answer 29

Question 30

What does the value of the standard error tell you?

Answer 30

Question 31

How to calculate number needed to treat?

Answer 31