Week 4- Introduction to Evidence

Question 1

What is internal validity?

Answer 1

• Conduct of the research

- Are you confident that the research was well conducted so that effect you notice is from exposure or intervention

Question 2

What is external validity?

Answer 2

-Generalisability of research findings from sample to reference population

Question 3

Describe the difference between chance, bias and confounders

Answer 3

Chance: Random error, cannot be eliminated but minimised through having smaller sample size
Bias: Systematic error, errors in way research was undertaken, cannot be eliminated
Confounders: variables not taken into account, influencing outcome

Question 4

What is marginal probability?

Answer 4

Probability of occurrence of single event

Question 5

What is joint probability?

Answer 5

Probability that 2 events will occur simultaneously

Question 6

What is conditional probability?

Answer 6

Probability of one event given another has occurred

Question 7

Describe sensitivity and what is the equation?

Answer 7

-Ability of a test to correctly identify positive results
-Sensitivity probability of test is positive when patients truly have disease
Sn= TP/TP+FN X 100

Question 8

Describe specificity and what is the equation?

Answer 8

-Ability of a test to correct identify negative results
-Specificity probability that test is negative when patients truly don’t have disease
Sp= TN/TN+FP x 100

Question 9

What is the true positive rate?

Answer 9

Patient has disease and test is positive

Question 10

What is the false positive rate?

Answer 10

Patient does not have disease but test is positive
-Probability that diagnostic test results will be positive given individual truly does not have the condition
(Specificity)

Question 11

What is the true negative rate?

Answer 11

Patient does not have disease and test is negative

Question 12

What is the false negative rate?

Answer 12

Patient has the disease but test is negative
-Probability that diagnostic test result will be negative given that individual truly has condition
(Sensitivity)

Question 13

What is the concept of odds ratio?

Answer 13

Measure of association between exposure and outcome
-Odds that outcome will occur given particular exposure when compared to odds of outcome occurring in absence of exposure

Question 14

What is the concept of risk ratio?

Answer 14

Measure of the risk of an outcome occurring in one group when compare to risk of same outcome occurring in another group

Question 15

What is risk difference?

Answer 15

• Absolute difference between the risks in each group

- Difference in rate of events between 2 groups

Question 16

How is risk difference related to the concept of Number Needed to Treat?

Answer 16

• NNT is a common measure used by health professionals, giving the number of people who need to receive the intervention for one additional person to experience or avoid an outcome
• Risk difference required to calculated NNT (NNT=1/RD)

Question 17

What does the 68-95-99.7 rule refer to, and what is its role in health care?

Answer 17

• Used for normal distribution (bell-shaped) curve only
• Compare individual data or results to match population
• 68% sit close to mean with 1 SD
• 95% sit close to mean with 2 SD
• 99% sit close to mean with 3 SD
• Comparing individuals to remaining population

Question 18

What is the purpose of the Central Limit Theorem?

Answer 18

• Cornerstone of statistics and research
• CLT addresses simple question of how can we use the data from sample and make inference for reference population
• States distribution of means is normal if sample size is large enough, regardless of underlying distribution of original measurements