Epidemiology, Biostatistics Flashcards

1
Q

Likelihood ratios
a) Used to assess what?
b) Definitions (positive vs negative)
c) How to calculate

A

a) Assesses 1. potential utility of a particular diagnostic test. 2. how likely it is that a patient has a disease or condition.

b) Positive likelihood ratio (LR+) = probability that a person with the disease tested positive for the disease (true positive) divided by the probability that a person without the disease tested positive for the disease (false positive).

Negative likelihood ratio (LR-) =
probability that a person with the disease tested negative for the disease (false negative) divided by the probability that a person without the disease tested negative for the disease (true negative).

c)
LR+ = sensitivity / 1 – specificity
LR- = 1 – sensitivity/specificity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Define effect size

A

Magnitude of the difference between groups. The absolute effect size is the difference between the mean outcomes in 2 different groups.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Define hazard ratio

A

A measure of how often a particular event happens in one group compared to how often it happens in another group, over time.
HR = 1 means lack of association, HR >1 suggests an increased risk, HR <1 suggests a smaller risk.
E.g. HR of 0.5 means that half as many patients in the group have an event at any point in time vs placebo proportionately.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Difference between predictive value & likelihood ratio?

A

PVs are affected by disease prevalence, but LRs are not.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly