Diesease Detectives L8: Misc & Statistics

sensitivity definition

measures accuracy of diagnostic test, if a patient actually has the disease, what is the probability the test will spot it?

sensitivity = ?

true positive) / (true positive + false negative)

what does the denominator of sensitivity represent? (TP+FN)

represents everyone who is actually sick

When Sensitivity = 1

he test is perfect at catching the disease, it will never miss a sick person

specificity definition

measures accuracy of diagnostic test, if a patient is perfectly healthy, what is the probability the test will correctly give a negative result?

specificity = ?

(true negative)/(true negative + false positive)

what does the denominator of specificity represent? (TN+FP)

represents everyone who is actually healthy

When Specificity = 1

it will never falsely accuse a healthy person of being sick

When designing/choosing a medical test what metrics do you have to balance?

they have to decide to balance whether a test should focus on minimizing false positives (high specitivity) or minimizing false negatives (high sensitivity) depending on real world consequences

Why do we need high specitivity? (helps avoid flase positives)

avoid giving treatment to those without disease, either due to price or possible dangers of treatment

Why do we need high sensitivity? (helps avoid false negatives)

need it incase the disease progresses or spread rapidly

PPV (Positive Predicted Value)

The share of true positives result among all positive results

PPV (Positive Predicted Value) Fomula VARIABLES

a=TP, b=FP

PPV (Positive Predicted Value) Fomula

(a/(a+b))

NPV (Negative Predicted Value)

The share of true negative results among all negative results

NPV (Negative Predicted Value) Formula VARIABLES

d=TN, c=FN

NPV (Negative Predicted Value) Formula

(d/(d+c))

Efficacy (What does it QUESTION/measure?) + Tested in what environment?

Can the treatment work?, Ideal and controlled (clinical trials)

Effectiveness (What does it QUESTION/measure?) + Tested in what environment?

Does the treatment work?, Real-world (general public)

Vaccine Efficacy + Tested in what environment?

percentage reduction in disease due to vaccine, ideal and controlled (clinical trial)

Attack Rate DEFINITION

proportion of an exposed population that develops a specific disease during a defined period/outbreak

Attack Rate Formula (expressed as percentage!)

AR = ((# of new cases of di)/(total # of people exposed/ at risk)) * 100

Herd Immunity

when a large portion of the population in immune to the disease which makes the likeliness of diease spread low

Herd Immunity Threshold (HIT) (%)

percentage of a population that needs to be immune to a disease in order for the population to have herd immunity

Herd Immunity Threshold: What does R_0 =?

basic reproductive number (average amount of people someone spread the disease to)

Herd Immunity Threshold Formula

HIT = 1-(1/r_0)

What do you specifically need to do to understand this concept?

practice problems!!