Risk Flashcards
Define prevalence probability?
Define incidence probability?
Prevalence probability- probability HAVING disease at given point in time
Incidence probability- probability GETTING disease during specified point in time
Define incidence rate?
Define hazard rate?
Incidence rate- Avg rate of change over time
Hazard rate- Instantaneous rate of change
State 2 ways to calculate probability?
p = no. favourable outcomes/all possible outcomes
p = no. of cases/total population
Define conditional probability?
How written?
Probability that something will happen given an event has already happened
E.g a patient will test positive IF they already have disease
Written P(A|B)
Define odds?
Roll fair dice
Cases/noncases
Eg. roll fair dice= 1:5=0.2
What does probability range from?
What does odds range from?
Prob- 0-1
Odds- 0 to infinity
- 1 indicate positive association
- 1 indicate no association
What does odds ration of 1 indicate?
What does odds ration of more than 1 indicate?
Odd ratio 1- no association
Odd ratio 1+- positive association
State issues using prevalence probability?
Length-time bias- conditions longer duration more likely captured
Diff in prev. can simply indicate shorter/longer duration disease or diff treatment success
Issues with incidence probability?
Issues competing risk- death due another cause
Ignore time to event
State risk difference and risk ratio:
Drug A- 0.6
Drug B- 0.2
Risk difference- 0.4 (40%)
Risk ratio- 3 (3x risk)
State absolute risk difference and relative risk difference:
Drug A- 0.6
Drug B- 0.2
Absolute risk difference- A-B= 0.4
Relative risk difference- (A-B/B)*100= 200%
Issues with relative risk?
Exaggerate risk
Don’t indicate baseline
Risk diff and ration give clearer sense impact/effect
Define relative risk?
ratio of the probability of an event occurring with an exposure versus the probability of the event occurring without the exposure.
How calculate relative risk- how much more likely?
Calculate relative risk?
Explain result:
RR of 1
RR greater 1
RR less 1
Further from 1 means?
RR=1 no association, no increased risk
RR greater 1= incidence exposed greater incidence non exposed- increased risk- positive association
RR less 1= incidence in exposed lower incidence in non exposed- decreased risk- negative association
Further from 1- stronger association
What makes something statistically significant?
p value less 0.05
If ci doesn’t include 1
When can’t calculate incidence in case control?
What use
50/50 way study designed
Use odd ratio
State equation odds?
Odds= Probability/(1-Probability)
Eg. 60% prob win race
Odds 1/5 (60:40)
Define RR
Define OR
with equation
State how calculate odds ration?
Calculate odd ratio
When to use odd ration?
Cohort or case control
How calculate odd ration in cohort?
How calculate odd ratio in case control?
Issue odds ratio?
Overestimate risk
Explain number needed to treat or harm?
Equation
If RD positive?
It is the number of people you need to treat in order to prevent one outcome
Indicate potential benefit of clinical intervention
NNT = 1/|RD|
RD is positive the intervention is harmful
RD for MI = 0.03-0.05 = -0.02
NNT = 1/|RD| = 1/0.02 = 50
Drug A prevents MIs but also increases risk of lung cancer:
RD = 0.02-0.01
NNH = 1/RD = 1/0.01 = 100
Meaning?
Need treat 50 with drug A prevent 1 heart attack
Need to treat 100 people with drug A to cause 1 lung cancer
Calculate NNH?
RD for MI = 0.03-0.05 = -0.02
NNT = 1/|RD| = 1/0.02 = 50
Drug A prevents MIs but also increases risk of lung cancer:
RD = 0.02-0.01
NNH = 1/RD = 1/0.01 = 100
Need treat 50 with drug A prevent 1 heart attack
Need to treat 100 people with drug A to cause 1 lung cancer
