Lecture 9 Flashcards
What does statistics do
let us quantify the uncertainty of these measures and determine how likely they are to indicate the truth
- estimate unknown quantity by using sample
What is mean
average of a set of measurements
- distorted by outliers
What is median
number that splits data into equal halves
What is mode
- number that occurs most often in data, can have more than one, not affected by outliers
Which central tendency to use when bell shaped?? when skewed?
mean
median
What are measures of variation
range, percentiles, sd
What is range
smallest and largest values
What is percentiles
- 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
What is standard deviation
- measure of dispersion for one variable that indicates an “average distance” between the values and the mean
from a boxplot how do you know its bell shaped
if median in centre of box
What are measures of frequency
- prevalence
- incidence - new cases/#at risk during interval
- incidence density - number of new cases in time period/total person time follow up
What is the equation for duration
duration = P/I
P = I * D
What is mortality rate
- how many people die from a disease in a given time (one year)
number of deaths due to disorder/number at risk
What is the case fatality rate
prop of people with disease who die within given time (one year)
number of deaths due to disorder / number with disorder
What is the problem with MRs and CFRs
don’t know if high or low, except in comparisons with other MRs and CFRs from other disorders
What is prop mortality rate
of deaths due to disorder / number of deaths from all disorders
why can PMRs increase over time
- more people may be dying from disorder
- fewer people dying from other causes
What is standardized mortality rate
- 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
How to interpret SMRs
less than one = disorder dying at lower rate than expected
greater than one = higher than expected death rate
How to compare MRs fairly?
age standardized morality rates
What are limitations of relative risk
same regardless of prevalence of the disorder
What is the meaning of Absolute risk reduction
decrease in risk of the treatment group compared to the control group
what is the meaning of NNT
number of people need to be treated to have one additional positive outcome
