Lecture 9

Question 1

What does statistics do

Answer 1

let us quantify the uncertainty of these measures and determine how likely they are to indicate the truth
- estimate unknown quantity by using sample

Question 2

What is mean

Answer 2

average of a set of measurements
- distorted by outliers

Question 3

What is median

Answer 3

number that splits data into equal halves

Question 4

What is mode

Answer 4

• number that occurs most often in data, can have more than one, not affected by outliers

Question 5

Which central tendency to use when bell shaped?? when skewed?

Answer 5

mean
median

Question 6

What are measures of variation

Answer 6

range, percentiles, sd

Question 7

What is range

Answer 7

smallest and largest values

Question 8

What is percentiles

Answer 8

• measure of dispersion for one variable that indicates the % of cases at or below a score or point
• ex: 25% p = value at which 25% of distribution/sample have that value or lower
• IQR

Question 9

What is standard deviation

Answer 9

• measure of dispersion for one variable that indicates an “average distance” between the values and the mean

Question 10

from a boxplot how do you know its bell shaped

Answer 10

if median in centre of box

Question 11

What are measures of frequency

Answer 11

• prevalence
• incidence - new cases/#at risk during interval
• incidence density - number of new cases in time period/total person time follow up

Question 12

What is the equation for duration

Answer 12

duration = P/I
P = I * D

Question 13

What is mortality rate

Answer 13

• how many people die from a disease in a given time (one year)

number of deaths due to disorder/number at risk

Question 14

What is the case fatality rate

Answer 14

prop of people with disease who die within given time (one year)

number of deaths due to disorder / number with disorder

Question 15

What is the problem with MRs and CFRs

Answer 15

don’t know if high or low, except in comparisons with other MRs and CFRs from other disorders

Question 16

What is prop mortality rate

Answer 16

of deaths due to disorder / number of deaths from all disorders

Question 17

why can PMRs increase over time

Answer 17

• more people may be dying from disorder
• fewer people dying from other causes

Question 18

What is standardized mortality rate

Answer 18

• ratio of number of observed deaths from given cause in a given time to the expected number of deaths
• doesn’t need to be compared to others

Question 19

How to interpret SMRs

Answer 19

less than one = disorder dying at lower rate than expected
greater than one = higher than expected death rate

Question 20

How to compare MRs fairly?

Answer 20

age standardized morality rates

Question 21

What are limitations of relative risk

Answer 21

same regardless of prevalence of the disorder

Question 23

What is the meaning of Absolute risk reduction

Answer 23

decrease in risk of the treatment group compared to the control group

Question 24

what is the meaning of NNT

Answer 24

number of people need to be treated to have one additional positive outcome

Question 25

what is odds ratio

Answer 25

used in case control to assess relationship between exposure and disease
- odds of exposure among cases compared to odds of exposure among controls

Question 26

What was the reprieve trial

Answer 26

• pitavastatin to prevent cardiovascular disease in HIV infection