day 3 Flashcards
What is risk?
the probability (usually statistical probability) that an event will occur in a group, whether it be a good or a bad event.
What is the probability is a player owns 1 out of 4 totl cards
The probability is an ordinary fraction (e.g., 1/4) that can also be expressed as a percentage (e.g., 25%) or as a proportion between 0 and 1 (e.g., p = 0.25).
What is the definition of Relative Risk (or Risk Ratio)?
The term ‘risk ratio’ is sometimes used because RR is calculated by dividing the probability of an event occurring for one group by the probability of an event occurring for a second group.
What is the deifiniton of odds
Odds are ratios of a player’s chances of losing to his or her chances of winning, or the average frequency of a loss to the average frequency of a win.
What are the odds in this example?
imagine we bought three tickets the probability of winning would be 3 in 4,
The odds would be 75 to 25. We can simplify this to 3 to 1. This means that the winning event is three times more likely to occur than not occur.
What are the distinctions between RR, OR , AR
RR is used to compare the risk in two different groups of people (e.g. smokers and non-smoker), usually used in prospective cohort studies.
OR is a measure of association between an exposure and an outcome (e.g. smoking and cancer), usually used in case-control studies and sometime in cohort studies (where the incidence is less than 10%).
AR is an individual risk of developing a disease over a time period (e.g. smokers and cancer), usually used for the number of events (such as a disease) that occurred in a group, divided by the number of people in that group.
What is the definition of relative risk?
RR is used to compare the risk in two different groups of people (e.g. smokers and non-smoker), usually used in prospective cohort studies and can increase or decrease the risk
What is the definition of ods ratio?
OR is a measure of association between an exposure and an outcome (e.g. smoking and cancer), usually used in case-control studies and sometime in cohort studies (where the incidence is less than 10%).
what is the definition of adverse risk
AR is an individual risk of developing a disease over a time period (e.g. smokers and cancer), usually used for the number of events (such as a disease) that occurred in a group, divided by the number of people in that group.
What is the definition of relative risk reduction RRR
describe the decrease in probability of an event occurring due to a lifestyle change or treatment.
When is RR used
statistical analysis of data from experimental, cohort and cross-sectional studies, to estimate the strength of the association between treatments or risk factors, and outcome. The RR value is used to test whether differences between groups are significant e.g. treatment and placebo or disease versus control. (we will discuss this in more detail later – essentially, we cannot really use RR in a significance test but we have a ‘work-around’ of sorts).
How can RR be calculated from AR?
RR= AR exposed/AR unexposed
What is probability useful for and not useful for?
- Useful to predict how often an outcome will occur
- Not useful to predict exactly when an outcome will occur
What is relative risk?
Ratio of probability of outcome occurring in an exposed group to the probability of the outcome occurring in an unexposed group
Are RR and OR interchangeable
- No
- OR can be used as an estimate of RR if rare disease
- Odds ratio is an overestimate if common disease
What is RR more useful for
Explaining success of a treatment for cardiac disease/osteoporosis- common
What is OR more useful for
Looking at probability of a rare side effect
What is absolute risk [AR]
- Individual risk
- Probability/chance of an event occurring
- Number of people in group who event occurs in/Total number of people in group
- Expressed in % or decimals
When is RR used
Prospective cohort studes
When is OR used
Retrospective
Case control studies
Cohort studies where incidence of event is less than 10%
When is AR used
Individual risk of developing a disease over a time period
Number of events in group/Number of people in group
RR formula
RR= (a/(a+b))/(c/(c+d))
What does it mean when RR<1 ?
Exposure decreases risk of outcome
What does it mean when RR >1 ?
Exposure increases risk of outcome
What type of outcome are odds and odds ratios related to?
Binary outcomes
What is the 95% confidence interval?
- Estimate of precision of OR and RR
- Range of values that you can be 95% sure contains the true mean value of the population
How do odds and probability compare for a common disease
Odds greater than probability
How do odds and probability compare for a rare disease?
Both are the same
- So OR is used in rare diseases to estimate RR
What happens if you use OR to estimate RR in common disease?
Will be greater than the true value of RR
Makes exposure seem better than it actually is for the outcome
overstate the effect of a treatment on an outcome measure
Difference between probability and odds
Denominator- just one section in odds, full pie chart in probability
How can RRR be calculated from AR?
AR unexposed - AR exposed) / AR unexposed
or ARR/AR exposed
How can RRR be calculated from RR?
RRR= 1- RR
How do ARR and RRR compare?
- RRR is constant across a range of absolute risks
- ARR is much higher in people with higher absolute risk
- ARR is much lower than RRR in people with low absolute risk
What does a relative risk of 0 mean?
Exposure is not associated with the outcome
Similarities for OR and RR?
Measure of association between outcome and exposure
Which is more commonly used in papers, RR or ARR? Why
Relative risk
Looks more impressive, bigger numbe
Can odds ratio be used for prospective or retrospective trials?
- Retrospective trials
- Prospective
