Flashcards in Biostatistics Deck (32)

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1

## Cross-sectional study

### What is happening at a particular point in time? Good for determining disease prevalence and risk factors.

2

## Case-control study

### What happened in the past? Compares a group with disease to a matched group without disease and searches for associations. Calculate Odds Ratio (OR).

3

## Cohort study

### Can be prospective (Who will develop disease?) or retrospective (Who developed disease?). Compares a group with a certain exposure/risk to a group without that exposure and asks who developed or will develop disease? Calculate Relative Risk (RR).

4

## Phase I of drug trial

###
Small number of healthy volunteers. Is it safe?

Assesses safety, toxicity, pharmacokinetics.

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## Phase II of drug trial

### Small number of patients with the disease of interest. Does it work?

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## Phase III of drug trial

### Large number of patients randomly assigned either to treatment or to best available treatment (standard of care). Is it as good as or better?

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## Phase IV of drug trial

### Post-marketing surveillance of patients after treatment FDA approved. Can it stay? Detects rare or long-term adverse effects.

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## Evaluation of diagnostic tests for sensitivity and specificity

###
---------Dz+ Dz-

Test+ TP (a) | FP (b)

Test- FN (c) | TN (d)

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## Sensitivity

### = a/a+c

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## Specificity

### = d/b+d

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## Positive predictive value (PPV)

### = a/a+b = true positive/all positives

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## Negative predictive value (NPV)

### = d/c+d = true negative/all negatives

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## Contingency table for quantifying risk

###
--------Dz+ Dz- (Disease/outcome)

Ex + a b

Ex - c d

(Exposure/Risk factor/Intervention)

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## Odds Ratio (OR)

###
= (a/c)/(b/d)= a*d/b*c

=Odds that the cases were exposed to risk versus the controls.

Used for case-control studies.

15

## Relative Risk (RR)

###
= [a/(a+b)] / [c/(c+d)]

= Risk of developing dz in the exposed group/ risk of developing dz in the unexposed group.

Used for cohort studies.

IF prevalence of disease is low, then OR approximately equals RR.

RRR= 1-RR

16

## Attributable risk (Absolute Risk Increase)

###
= [a/(a+b)] - [c/(c+d)]

= The difference in risk between the exposed group and unexposed group (or the difference in risk attributable to the exposure).

Used to calculate the NNH.

17

## Relative risk reduction (RRR)

###
= 1 - RR

= 1- [a/(a+b)] / [c/(c+d)]

= Proportion of risk reduction attributable to the intervention.

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## Absolute Risk Reduction (ARR)

###
= [c/(c+d)] - [a/(a+b)]

= The difference in risk between the unexposed group and the exposed group (or the difference in risk attributable to the intervention).

Used to calculate the NNT.

19

## Number Needed to Treat (NNT)

###
NNT = 1/ Absolute Risk Redution

= the number of patients that need to undergo an intervention for 1 patient to benefit.

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## Number Needed to Harm (NNH)

###
NNH = 1/ Attributable Risk

= the number of patients that need to be exposed to a risk factor (or intervention) for 1 patient to be harmed.

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## Incidence

### = # new cases in a time period/# of ppl at risk

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## Prevalence

### = # existing cases at one point in time/ # of ppl at risk

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## True negative

###
=Specificity * # pts without disease

= [d/b+d]*(b+d)

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## True positive

###
=Sensitivity * # pts with disease

=[a/a+c] *(a+c)

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## Positive likelihood ratio

### =Sensitivity/ (1 - Specificity)

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## Negative likelihood ratio

### =(1 - Sensitivity)/Specificity

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## 95% Confidence Interval

### = mean +/- 1.96 *SD/sqrt(n)

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## Type I error

### Occurs when research rejects the null hypothesis (finds a difference), but the null hypothesis is true (there is no real difference). Aka a FALSE POSITIVE ERROR.

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## Alpha

### The probability of making a Type I error

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