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GYO Boards > Stats > Flashcards

Stats Flashcards

1
Q

Sensitivity?

A

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

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2
Q

Specificity?

A

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

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3
Q

Positive predictive value?

A

TP/(TP+FP)

The proportion with positive test results who have the disease

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4
Q

Negative predictive value?

A

TN/ TN+FN

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

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5
Q

How does prevalence change sensitivity and specificity?

A

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

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6
Q

What are alpha and beta errors?

A

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

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

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7
Q

Power?

A

1-Beta error

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8
Q

FP rate?

A

FP/ FP+TP

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9
Q

FN rate?

A

FN/ FN+TN

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10
Q

How does sensitivity relate to FNR?

A

Sensitivity= 1-FNR

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11
Q

How does specificity relate to FPR?

A

SPP= 1- FPR

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12
Q

What is the odds ratio?

A

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)

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13
Q

Relative Risk?

A

Probability of exposed to the probability of not exposed

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

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14
Q

Attributable Risk?

A

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)]

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15
Q

Likelihood ratio?

A

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

Positive LR = sensitivity / (100 – specificity)

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16
Q

Incident rate?

A

Number of cases in specific time / population of risk

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17
Q

RR or OR = 1.0 means?

A

No association of risk with disease

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18
Q

What does a regression analysis do?

A

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

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19
Q

Number Needed to Treat (NNT)

A

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

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20
Q

Student t-test

A

Measure difference between two groups

21
Q

Paired t-test

A

measures difference in the mean of two paired tests

22
Q

Mann-Whitney (Wilcoxon Rank Test)

A

Non-parametric analogue

23
Q

ANOVA

A

more than 2

24
Q

Chi Square

A

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

25
Q

Fischer Exact test

A

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

26
Q

Log-rank

A

compares survival rate among groups (Kaplan-Meier Curve)

27
Q

Cox regression

A

multivariate analyses control confounding variables

28
Q

McNemmer test

A

used to measure sample size

29
Q

Question: how to decrease type I error?

A

Increase sample size

30
Q

ROC: Receiver Operator Characteristic?

A 
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)
31
Q

Best initial test?

A

Case control

32
Q

Test for normally distributed data?

A

SD

33
Q

Incidence vs. Prevalence

A 
Incidence= New cases = # of cases/ Sum time period
Prevalence= # of cases= # ppl with disease/Population.
34
Q

Criteria for establishing a screening program:

A

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

35
Q

Two basic study designs:

A

1.Experimental: clinical trials

2.Observational

36
Q

Advantages, disadvantages of cohort vs. case control

A

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

37
Q

How to control a Sampling Bias?

A

Sampling a control in a population at risk

38
Q

Mean vs Median vs. Mode

A

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

39
Q

SD?

A 
Standard of deviation (SD): deviation from the mean
Variance: 
SD is the square root of variance
(V=(SD)2)
SD= ⎇V
40
Q

SE?

A

Standard of Error: SD divided by the square root of N

SE= SD/ ⎇N

41
Q

Z-score?

A

Z-Score: number of SD that falls from the mean

Z-Score = = sample mean - population mean/ SD/ ⎇N (standard error)

42
Q

CI?

A

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

43
Q

HR?

A

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

44
Q

Kaplan-Meier?

A

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

45
Q

Cox(Proportional Hazards)Regression?

A

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

46
Q

Median survival?

A

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

47
Q

How to conduct a RCT?

A

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

48
Q

Weaknesses of RCT?

A

Weaknesses of RCT:
Expensive
Time consuming
More patients

GYO Boards (12 decks)

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