Stats

Question 1

Sensitivity?

Answer 1

TP/(TP+FN): Proportion with disease correctly identified

Question 2

Specificity?

Answer 2

TN/(TN+FP): Proportion without disease correctly identified

Question 3

Positive predictive value?

Answer 3

TP/(TP+FP)

The proportion with positive test results who have the disease

Question 4

Negative predictive value?

Answer 4

TN/ TN+FN

The proportion with negative test results who don’t have the disease

Question 5

How does prevalence change sensitivity and specificity?

Answer 5

Higher prevalence doesn’t change sensitivity or specificity but increases PPV and decreases NPV.

Question 6

What are alpha and beta errors?

Answer 6

Reject the null hypothesis and it’s true —> alpha error

Not reject the null hypothesis and it’s false —> beta error

Question 7

Power?

Answer 7

1-Beta error

Question 8

FP rate?

Answer 8

FP/ FP+TP

Question 9

FN rate?

Answer 9

FN/ FN+TN

Question 10

How does sensitivity relate to FNR?

Answer 10

Sensitivity= 1-FNR

Question 11

How does specificity relate to FPR?

Answer 11

SPP= 1- FPR

Question 12

What is the odds ratio?

Answer 12

It tells you how the presence or absence of property X has an effect on the presence or absence of property Y.

B/D (odds a control exposed)

CxB (# times event didn’t)

Question 13

Relative Risk?

Answer 13

Probability of exposed to the probability of not exposed

C/(C+D) (probability of not exposed getting dz)

Question 14

Attributable Risk?

Answer 14

Excess risk of the outcome (e.g. disease) in the exposed group compared with the non-exposed group

AR = [a/(a+b)] – [c/(c+d)]

Question 15

Likelihood ratio?

Answer 15

The probability of detecting cancer to the probability of not detecting cancer.

Positive LR = sensitivity / (100 – specificity)

Question 16

Incident rate?

Answer 16

Number of cases in specific time / population of risk

Question 17

RR or OR = 1.0 means?

Answer 17

No association of risk with disease

Question 18

What does a regression analysis do?

Answer 18

Predicts or estimates a value of one variable corresponding to the given value of another variable.

Question 19

Number Needed to Treat (NNT)

Answer 19

Number Needed to Treat (NNT): numbers needed for a screening test to detect one case to treat OR the number of vaccinations to prevent one case of disease. Ideal = 1

NNT=1/ Absolute risk reduction

E.g. drug reduces bad outcome from 50% to 40%
ARR= 0.5-0.4=0.1
NNT= 1/0.1 = 10

Question 20

Student t-test

Answer 20

Measure difference between two groups

Question 21

Paired t-test

Answer 21

measures difference in the mean of two paired tests

Question 22

Mann-Whitney (Wilcoxon Rank Test)

Answer 22

Non-parametric analogue

Question 23

ANOVA

Answer 23

more than 2

Question 24

Chi Square

Answer 24

difference between two or more proportion variables or percentage of categorical outcome

Question 25

Fischer Exact test

Answer 25

replaces chi square when numbers are small, only two responses (death/alive)

Question 26

Log-rank

Answer 26

compares survival rate among groups (Kaplan-Meier Curve)

Question 27

Cox regression

Answer 27

multivariate analyses control confounding variables

Question 28

McNemmer test

Answer 28

used to measure sample size

Question 29

Question: how to decrease type I error?

Answer 29

Increase sample size

Question 30

ROC: Receiver Operator Characteristic?

Answer 30

``` ROC: Receiver Operator Characteristic True Positive against False positive Closer to the left border is more accurate Close to 45 degree is less accurate (1.0 excellent test, 0.5 worthless) ```

Question 31

Best initial test?

Answer 31

Case control

Question 32

Test for normally distributed data?

Answer 32

SD

Question 33

Incidence vs. Prevalence

Answer 33

``` Incidence= New cases = # of cases/ Sum time period Prevalence= # of cases= # ppl with disease/Population. ```

Question 34

Criteria for establishing a screening program:

Answer 34

 1.    Target disease burden the population   2.    Known natural history 3.    Treatment available     4.    Early detection improves outcome     5.    Screening method must be acceptable     6.    Cost feasible

Question 35

Two basic study designs:

Answer 35

    1.    Experimental: clinical trials |     2.    Observational

Question 36

Advantages, disadvantages of cohort vs. case control

Answer 36

A. Cohort (prospective) Advantage: cheap and feasible Disadvantage: can’t blind and can’t find control B. Case control (Retrospective) Advantage: use when outcome is rare Disadvantage: retrospective can’t account for variables

Question 37

How to control a Sampling Bias?

Answer 37

Sampling a control in a population at risk

Question 38

Mean vs Median vs. Mode

Answer 38

Mean: average Median: value in the middle separates above and below Mode: Most repeated number

Question 39

SD?

Answer 39

``` Standard of deviation (SD): deviation from the mean Variance: SD is the square root of variance (V=(SD)2) SD= ⎇V ```

Question 40

SE?

Answer 40

Standard of Error: SD divided by the square root of N | SE= SD/ ⎇N

Question 41

Z-score?

Answer 41

Z-Score: number of SD that falls from the mean | Z-Score = = sample mean - population mean/ SD/ ⎇N (standard error)

Question 42

CI?

Answer 42

CI: tells the most likely mean of a population, how much the average value fluctuate 95% CI: 95% chance to contain the true mean of the population 99% is wider. 100% is all the population

Question 43

HR?

Answer 43

Hazard ratio: HR the ratio of hazard rates corresponding to the two conditions described. HR of 1: both groups experiencing the same events HR 0.33: one group experiencing 1/3 of the events HR >1 or <1: the survival was better in one group than the other

Question 44

Kaplan-Meier?

Answer 44

Kaplan–Meier: is a non-parametric statistic used to estimate the survival function from lifetime data.

Question 45

Cox (Proportional Hazards) Regression?

Answer 45

Cox (Proportional Hazards) Regression. ... Cox regression: is method for investigating the effect of several variables upon the time a specified event takes to happen.

Question 46

Median survival?

Answer 46

Median survival: It is the time expressed in months or years when half (50%) the patients are expected to be alive.

Question 47

How to conduct a RCT?

Answer 47

How to conduct a RCT     1.    Hypothesis     2.    Frame design, population, outcome what

Question 48

Weaknesses of RCT?

Answer 48

Weaknesses of RCT: Expensive Time consuming More patients