Statistics

Question 1

What is sensitivity and how is it calculated?

Answer 1

• How good is a test for the condition of interest.
• True positive rate.
• Negative result in high sensitivity test useful for rulng condition out.
• Sens = T+/(T+ + F-)

Question 2

What is specificity and how is it calculated?

Answer 2

• How good is a test for the condition of interest?
• True negative rate.
• Positive result in highly specific test useful for ruling in disease.
• Spec = T-/(T- + F+)

Question 3

What is a positive predictive value and how is it calculated?

Answer 3

• How good is the test?
• If the test is positive what is the chance of the patient having the disease?
• PPV = T+/(T+ + F+)

Question 4

What is a negative predictive value

Answer 4

• How good it the test?
• If the test is negative what is the chance the patient does not have the disease?
• NPV = F-/(F- + T-)

Question 5

What is a likelihood ratio and how is it calculated?

Answer 5

• Assess the value of performing a diagnostic test.
• Use sensitivity and specificity to determine whether test result usefully changes the probability that a condition exists.
• +LHR = sensitivity/(100% - specificity)
• -LHR = (100% - sensitivity)/specificity

Question 6

What is incidence?

Answer 6

• Incidence is a rate –> cases per 5 years.

Question 7

What is prevalence?

Answer 7

• Prevalence is a cross section in time.

Question 8

What is relative risk and how is it calculated?

Answer 8

• Ratio of an outcome between 2 exposures.
• Probability of an event occurring in an exposed group compared to an unexposed group.
• RR = (a/a+b)/(c/c+d)

Question 9

What is odds ratio and how is it calculated?

Answer 9

• Odds like the TAB.
• Event occurring:event not occurring.
• Does not take in to account total events.
• Useful when population risk unknown.
• With low prevalence OR ~ RR.
• OR = ad/cb

Question 10

What is the absolute risk and how is it calculated?

Answer 10

• Real difference in absolute terms between 2 groups.

- AR = (c/c+d) - (a/a+b)

Question 11

What is a type I error?

Answer 11

• a error
• False positive.
• Reject the null hypothesis when it is actually true.
• p-value quantifies risk of rejecting the false hypothesis.

Question 12

What is a type II error?

Answer 12

• b error
• False negative.
• Fail to reject the null hypothesis when it should have been rejected.
• Greatest risk of making type II error is underpowering.

Question 13

What determines the power of a test?

Answer 13

• Population size.
• Size of effect.
• Variance within populations.

Question 14

What is phase 0 of a drug trial?

Answer 14

• PK and PD in humans.

- Small sub-therapeutic doses given.

Question 15

What is phase 1 of a drug trial?

Answer 15

• Safety.
• Small number.
• Safe dosing and adverse affects.

Question 16

What is phase 2 of a drug trial?

Answer 16

• Safety and efficacy.
• 2a dosing requirements.
• 2b efficacy.
• Also test toxicity.

Question 17

What is phase 3 of a drug trial?

Answer 17

• Confirmation of safety and efficacy.
• Large numbers.
• Vs. placebo RCTs - often >1.
• Input from licensing committees.

Question 18

What is phase 4 of a drug trial?

Answer 18

• Contiuned pharmacovigilance.
• New uses/populations.
• Paediatrics.
• Interactions.

Question 19

What are case control studies used for?

Answer 19

• Used to estimate the odds (OR) of developing the studied condition/disease.
• Can determine if there is an associational relationship between condition and risk factor.
• Cannot establish causality.

Question 20

What are randomised controlled trials used for?

Answer 20

• “Gold standard” in medical research.
• Best for answering questions about effectiveness of different therapies or interventions.
• Widely considered the gold standard for establishing causality.

Question 21

What are cohort studies used for?

Answer 21

• Establish causation of a disease or evaluate the outcome/impact of treatment.
• Used when randomised controlled clinical trials are not possible.