HMB342 Lecture 3 Screening Methods

What are some forms of screening?

physical examination, imaging (ie. x-ray or mri), blood or urine test, genetic test, pcr test

The relationship between disease status and test result can be organized using a __________ ________

contigency table

What is sensitivity?

the proportion of diseased individuals who are correctly identified as positive

What is specificity?

the proportion of healthy individuals who are correctly identified as negative in the population

What is the formula for sensitivity?

TP/(TP + FN)

True Positives/True Positives + False Negatives (total number of disease cases)

What is the formula for specificity?

TN/(TN + FP)

True Negatives/True Negatives + False Positives (total number of healthy individuals

What question do sensitivity and specificity answer?

How good is the test at identifying people with the disease and people without the disease?

What is positive predictive value?

How likely is it that we actually have the disease given a positive test result

What is the formula for positive predictive value?

PPV = TP/ TP + FP

(# of people who have disease and test positive/ total # of people who test positive)

What is the negative predictive value?

The probability that a person who tests negative for the disease truly does not have the disease

What is the formula for negative predictive value?

NPV = TN/ TN + FN

(# of people who test negative/ number of people who are truly negative)

What is validity?

measures what degree the measurement system measures what it intends to measure (accuracy)

What is reliability?

measures the consistency of the measurement system (precision)

What is case fatality % formula?

number of individuals dying during a specified period of time after disease onset or diagnosis/number of individuals with the specified disease

What is person-years?

unit used for counting observations related to mortality rates, incidence rates, etc.

What is five-year survival/ n-year survival?

the proportion of patients that are alive 5 (or n) years after the diagnosis

What is the problem with 5-year survival measurements?

we don't know the actual onset of the disease and only the time when it was diagnosed, and the time of diagnosis can impact how long you have survived the disease

What are life tables used for?

used primarily by actuaries to estimate risks to calculate insurance premiums, etc.

What is the formula for relative survival?

relative survival = observed survival in people with disease/expected survival if disease was absent

What are the assumptions made when survival is calculated?

1) no changes over time to effectiveness of the treatment over study duration

2) individuals who are lost to follow-up are on average the same as those who are not (no attrition bias)

3) If only collecting data once a year (or once a month, etc. we assume that events occur uniformly between collection dates and that there is no sudden changes in risk within each period)

Why is survival data normally not generalizable?

many studies are prone to selection bias, participants in the study are not representative of the general population you want to generalize your results to (ie. the study is done in a hospital where individuals are on average sicker).