Flashcards in Biostatistics Deck (69):

1

## What does Prevalence, Incidence and Attack Rate tell us?

### What is the frequency of disease in a population?

2

## What does Sensitivity and specificity tell us?

### How well does a test differentiate sick from healthy people?

3

## What does predictive value tell us?

### Of those in a population who test as sick of healthy, how many are truly sick or healthy?

4

## What does Risk Reduction/Increase and Number-needed-to-treat/harm tell us?

### What is the impact of a medicine/treatment?

5

## What does point prevalence help us understand?

### Disease burden or extent of a health problem.

6

## What is prevalence?

### [Number with a disease at a specific point in time]/[Number at risk of illness during that time period]

7

## What is period prevalence?

### Prevalence during a period of time

8

## What is lifetime prevalence?

### Prevalence over the course of a lifetime

9

## What does incidence help us understand?

### The risk of a specific health event

10

## What is incidence?

### [Number of NEW people with DZ during a time period]/[Number at risk of illness during that time period]

11

## What is the main measure of acute diseases?

### Incidence

12

## What helps determine causation?

### Incidence

13

## What is cumulative incidence?

### Total number reported over time

14

## What is Attack Rate?

### Refers to outbreaks - similar to prevalence over a very short period of time

15

## When is Attack Rate used?

### When the nature of disease is acute and population observed for short period of time (ex. outbreaks, specific exposures)

16

## How do you calculate Attack Rate?

### [Number new cases]/[Number exposed]

17

## How do you calculate Secondary Attack Rate?

### [Number new cases]/[Number exposed - primary cases]

18

## What does Secondary Attack Rate measure?

### Person to person spread of disease after initial exposure

19

## What is Secondary Attack Rate similar to over a very short period of time?

### Incidence

20

## What affects prevalence and incidence?

###
-Duration of illness (longer --> higher prevalence)

-Number of new cases (more new cases --> higher prevalence) - incidence high

-Migration - In (ill --> higher prevalence); Out (well --> higher prevalence)

-->Recovery and death --> lower prevalence

-Prevention --> lower incidence

-Changes in diagnostic criteria or reporting

21

## What is the relationship between prevalence and incidence if the disease is long term (ex. diabetes)?

### Prevalence > Incidence

22

## What is the relationship between prevalence and incidence if the illness is acute (ex. flu)?

### Prevalence ~ Incidence

23

## What is sensitivity?

### The probability that a diseased person will be identified correctly by a diagnostic/screening test

24

## What is another name for sensitivity?

### True-positiive probability or true-positive rate

25

## What is the equation for sensitivity?

### True Positives/ Total # of ill people

26

## What should you remember with Sensitivity?

### SNOUT - High sensitivity rules disease out

27

## What is the total number of ill people?

### True positives + False negatives

28

## What is Specificity?

### Probability that a well (non-diseased) person will be identified correctly by a diagnostic/screening test

29

## What is another name for specificity?

### True-negative probability

30

## What is the equation for specificity?

### True negatives/total # of well people

31

## What should you remember with Specificity?

### SPIN - High specificity disease rules in

32

## What is the total # of well people?

### TN + FP

33

## What does a high sensitivity test err on the side of?

### Over-diagnosing

34

## What does a high specificity test err on the side of?

### Under-diagnosing

35

## What should you remember with high sensitivity tests?

###
-Identify most or all possible disease cases; may identify some healthy people as sick

-Most useful when under-diagnosing may lead to severe consequences (ex. fast developing cancers)

36

## What should you remember with high specificity tests?

###
-Identify most or all well people; may miss some of the sick people

-Most useful when over-diagnosing leads to dangerous, painful or unnecessary treatment

37

## What is a predictive value?

### Probability that a test will give the correct diagnosis

38

## What does predictive value depend on?

###
-Test sensitivity and specificity; prevalence of the DZ in the population being tested

-Predictive values will vary from population to population and study to study

39

## What is Positive Predictive Value?

### Probability that a person who tests positive for a disease truly has it (is really sick)

40

## What is the equation for PPV?

### PPV = TP/(TP + FP) --> Top row of a 2x2 table

41

## What is the equation for NPV?

### NPV = NP/(NP + FN) --> Bottom row of a 2x2 table

42

## What is Negative Predictive Value?

### Probability that a person who tests negative for a disease truly is well

43

## How does High prevalence relate to predictive value?

###
-Higher disease prevalence --> Higher PPV (greater chance that positive test result reflects true illness)

--> Lower NPV (lower change that negative test reflects disease-free status)

44

## How does Low prevalence relate to predictive value?

###
-Lower disease prevalence --> Lower PPV (lower chance that positive test result reflects true illness)

--> Higher NPV (greater chance that negative test result reflects disease-free status)

45

## When is Risk Reduction and Number-Needed-To-Treat relevant?

### When comparing effects in randomized controlled trials.

46

## Why are we interested in Risk Reduction and Number-Needed-To-Treat?

### Interested in understanding risk of treatment vs. no treatment

47

## What are we asking in Risk Reduction and Number-Needed-To-Treat studies?

### What is the frequency of bad outcomes in group being treated compared to the group not being treated?

48

## Randomized Controlled Trials (RCT):

###
-Have at least one treatment group and one control group

-People in both groups may have positively (placebo effect) or negatively (harmful effects)

-How do we compare different group response rates?

49

## What is Control Event Rate (CER)?

### Proportion of control group participants who have a bad outcome after "treatment" (ex. placebo or no rx)

50

## What is the CER if 10 of 30 control group participants become sicker?

### CER = 10/30 = 33% have adverse outcomes

51

## What is Experimental Event Rate (EER)?

### Proportion of treatment group participants who have a bad outcome after treatment (ex. new drug)

52

## What is the EER if 4 of 30 treatment groups become sicker?

### EER = 4/30 = 13% had adverse outcomes

53

## What is Absolute Risk?

### "risk difference" = difference in risk of developing a DZ or undesired outcome after treatment

54

## How do you calculate Absolute Risk?

### CER-EER

55

## What is an Absolute Risk Reduction (ARR)?

### When CER > EER - higher rate of adverse outcomes in control group --> sometimes referred to as "attributable risk"

56

## What is an Absolute Risk Increase (ARI)?

### When EER > CER - higher rate of adverse outcomes in treatment group

57

## What is Relative Risk?

### "risk ratio" = proportion of treatment group risk to control group risk

58

## How do you calculate Relative Risk?

### EER/CER

59

## How does risk of bad outcome change in the treatment group with RR?

###
Risk Increases when RR > 1

Risk Decreases when RR

60

## What is Relative Risk reduction/increase?

### Difference in 2 event rates, as a proportion of the event rate in the control group

61

## What is the equation for Relative Risk Reduction/Increase?

### 1-RR or AR/CER

62

## What is the equation for Relative Risk Reduction?

### CER > EER

63

## What is the equation for Relative Risk Increase?

### EER > CER

64

## What is Number Needed To Treat (NNT)?

### Number of patients who need to be treated to get 1 additional patient a favorable outcome

65

## What is the equation for NNT?

### NNT = 1/ARR

66

## Explain what NNT = 5 means?

### For every 5 people treated, 1 more person would respond to the drug

67

## What is Number Needed to Harm (NNH)?

### Number of patients who, if they were treated, would result in 1 additional patient being harmed

68

## How does NNH relate to ARI?

### NNH = 1/ARI

69