Statistics

Question 1

PPV and NPV changes with prevalence

Answer 1

PPV will rise with higher prevalence

NPV will rise with lower prevalence

Question 2

Positive and negative likelihood ratio equation

Answer 2

Positive: sens/ (1-spec)
Negative: (1-sens)/ spec

Question 3

Clinical trials phases 0-4

Answer 3

Phase 0: prelim PK/PD info
Phase 1: healthy volunteers for safety and toxicity, PK, PD
Phase 2: larger to look at dose and efficacy
Phase 3: RCT for efficacy (cf good standard)
Phase 4: post marketing survellience for safety vigilance

Question 4

Adoption vs twin studies

Answer 4

Adoption to look at genetic influences in same environment

Twin studies to review affects of genes (mono vs diz)

Question 5

Cohort studies down side

Answer 5

Prone to loss to follow up

Question 6

Pre registration of trials prevents?

Answer 6

Publication bias

Question 7

Type 1 and 2 error

Answer 7

1 error concluding there is different when one doesn’t exist (p value) “false positive”
2 error concluding there is no difference when there is one (power) “false negative”

Question 8

SD 1 standard deviation and 2 standard deviation (percentage)

Answer 8

1: 68% (16% above and 16% below)
2: 95%
3: 99.7%

Question 9

What is variance?

Answer 9

SD squared

Question 10

Intention to treat important why

Answer 10

Underestimated true effect

Maintains randomisation to overcome selection bias

Question 11

Pre test odds take into account

Answer 11

Patient characteristics and prevalence

Question 12

Multivariate analysis two groups

Answer 12

Multiple regression (continuous variable)
Logistic regression (dichotomous)

Question 13

Size of box on forest plot

Answer 13

Related to quality and size of study

Question 14

Your region has a birth rate of about 50,000 babies per year. About 50 preschool children are diagnosed
each year with “crumblitis”, a rare gastrointestinal disorder, the cause of which is unknown. You hypothesise
that this condition is related to maternal ingestion of orange rhubarb during pregnancy.
Which one of the following is the most appropriate research design to test your hypothesis?

Answer 14

Case control

Question 15

SIDS percent of deaths

Answer 15

7%

Question 16

Severe disability rate

Answer 16

1/25

Question 17

Children with chronic condition

Answer 17

37%

Question 18

2003 (a) QUESTION 53
What is the greatest strength of the case-control study design?
A. Controls for bias.
B. Controls for confounding.
C. Feasible with small or moderate numbers.
D. Multiple endpoints can be assessed.
E. Multiple risk factors can be assessed.

Answer 18

Case control is comparing characteristics of those with disease/ outcome to a control
group without
This is good for conditions of low prevalence where it would take a very long time to
collect enough numbers in a RCT
In general determinesassociatiations rather than causation (esp if exposure occurred in
past)
ANSWER = C

Question 19

P value ‘significance’

Answer 19

0.05
The smaller the p value the smaller the chance that the null hypothesis is true (null meaning no difference between the groups and most studies are trying to reject this)

Question 20

High correlation if r =

Answer 20

0.6-0.8
Rsquared is the percentage of data related to intervention with a correlation change
Correlation is strength between two variables
Regression quantifies it (straight line through scatter)

Question 21

What is kappa

Answer 21

Level of agreement when 1 is perfect agreement (0.5 or more is good)

Question 22

Incidence vs prevalence

Answer 22

Incidence is NEW diagnoses

Prevelance is overall

Question 23

Chi squared is

Answer 23

Looking at if there is a significant difference between two categorical variables