Module 4 Flashcards
Sensitivity =
Ability to correctly screen or diagnosis a condition TRUE POSITIVES
Specificity
Ability to correctly screen OUT people WITHOUT the condition
TRUE NEGATIVES
Sensitivity Calculation
A/(A+C)
A= true positives / everyone with disease (true + & false -)
Specificity Equation
D/(B+D)
true negatives divided by everyone who doesn’t have the disease (false - & true -)
What would calculation be for sensitivity and specificity
Sensitivity = a/(a+C) 18 / (18+2) = .9 = 90%
Specificity =
d/(b+d) = 76/(4+76) = 76/80 = 0.95 = 95%
Cohort Study vs Case-control study
Cohort - real time following of individuals
Case-control = look back at exposure you are testing
Cohort study statistic =
relative risk
case-control study statistic =
odds ratio
Relative risk tells you what
incidence of outcome with exposure
RR=1 same as exposed vs unexposed
> 1 = exposed group higher risk
< 1 = exposed group lower risk
RR = 0.80 how would you interpret this
(1-0.8)*100 = 0.2
0.2 * 100 = 20%
20% of subjects
RR = 2.38 & 4.46 how do you interpret
4.46 group 4.46 times more likely to acquire what is being tested
What does Odds Ratio tell you
how many times more likely the odds of finding an exposure in someone with the disease vs someone without the disease
OR = 1
OR >1
OR<1
1 no increase
>1 increased frequency
< 1 decreased frequency of finding disease in the exposed group
survival analysis =
method used to examine duration of time until an event occurs
Censored Data =
those who don’t have the event during the study or drop out of study
Kaplan Meier Curve
nonparametric
X axis time
y axis proportion of sample that have not had the event (could be death or something else that is being measured)
TEST “A” RESULTS TEST “B” RESULTS
Confirmed HIV positive Confirmed HIV negative Confirmed HIV positive Confirmed HIV negative
Test A: positive 10 5 Test B: positive 13 3
Test A: negative 2 20Test B: negative 2 17
Calculate sensitivity for test A
calculate specificity for test A
10/(10+2) = 0.83333
20/(5+20) = 0.8
TEST “A” RESULTS TEST “B” RESULTS
Confirmed HIV positive Confirmed HIV negative Confirmed HIV positive Confirmed HIV negative
Test A: positive 10 5 Test B: positive 13 3
Test A: negative 2 20 Test B: negative 2 17
Calculate sensitivity for TEst B
Calculate Specificity for Test B
sensitivity 13/(13+2) = 0.8667
specificity 17/(3+17) = 0.85
A researcher has developed a new rapid test for covid 19. She evaluates her new test by testing 100 patients with both her rapid test and the gold standard lab test. She calculates her specificity to be 94%. What does this tell you?
The rapid test resulted in a negative result when the person truly did not have covid19 94% of the time (true negatives)
