EBM Tables and Equations

Question 1

Prevalence =

Answer 1

(total #sick)/(total population)

• how many people are sick
• a single time point
• Prevalence can be used to estimate the likelihood of a diagnosis before any “tests”

Question 2

Cumulative incidence:

Answer 2

(new cases)/(total population at risk at study start)

• how many people are getting sick (NEW CASES)
• incidence is a rate, it happens over a time interval

Question 3

Incidence equation in steady state:

Answer 3

prevalence / duration

Question 4

Duration equation in steady state:

Answer 4

prevalence / incidence

Question 5

Prevalence equation in steady state:

Answer 5

(incidence) X (average duration)

Question 6

alpha =

Answer 6

• the probability you’ll make a false hit.
• Arbitrarily, p = 0.05
• false hit = type 1 error
• 5% of the time, we’ll make an error

Question 7

beta =

Answer 7

• probability you won’t find a difference when one actually exists (false miss)
• false miss = type 2 error
• probability of missing a reality

Question 8

power =

Answer 8

1 - beta

• power of study to pick up a study when it actually does exist
• Low power is a common reason for type II errors.

Question 9

2 X 2 tables for hypothesis testing:

(alpha, beta, and power)

Answer 9

Question 10

2 X 2 tables for hypothesis testing:

(type 1 and 2 errors)

Answer 10

Question 11

2 X 2 tables for hypothesis testing:

(false hits and false misses)

Answer 11

Question 12

95% CI equation:

Answer 12

95% CI = mean +/- 1.96(SEM)

• SEM = SD/ √n

Question 13

Standard error of the mean (SEM) eqaution:

Answer 13

SEM = SD/ √n

• SD = standard deviation
• n = sample size

Question 14

The three types of prevention:

Answer 14

1. Primary: before exposure (PREVENT)
2. Secondary: after exposure (SCREEN)
3. Tertiary: after disease process occurs (TREAT)

Question 15

Standard deviation:

+/- 3SD contains –% of observations

Answer 15

99.7%

Question 16

Standard deviation:

+/- 1SD contains –% of observations

Answer 16

68%

Question 17

Standard deviation:

+/- 2SD contains –% of observations

Answer 17

95%

Question 18

The three types of variation:

Answer 18

• Overall variation:
  
  • measurement variation + biological variation
• Measurement variation:
  
  • instrument variation + observer variation
• Biological variation:
  
  • intra-individual and inter-individual

Question 19

The dependent variable is on what axis?

Answer 19

Y-axis

Question 20

The independent variable is on what axis?

Answer 20

X-axis

Question 21

Regression r-value close to 0:

Answer 21

no association

Question 22

Regression r-value close to 1:

Answer 22

strong association

Question 23

Regression r-squared value tells you:

Answer 23

• the amount of variation in Y that is contributed by variation in X.

Question 24

Three ways you can control for outliers:

Answer 24

1. using non-parametric test
2. dropping the outlier(s)
3. log transformation

Question 25

Variance =

Answer 25

measure of the spread/dispersion of values around the mean.

Question 26

Standard deviation =

Answer 26

**√v; (v = variance)** * decreases as sample size increases

Question 27

Standard error of the mean (SEM) =

Answer 27

**SD/ √n**

Question 28

Equation for 95% CI:

Answer 28

**95% CI = mean +/- 1.96(SD/ √n)** * SD = standard deviation * n = sample size

Question 29

For correlation analyses, the confidence interval cannot contain:

Answer 29

0 0 = no correlation

Question 30

For relative risk, hazard ratios, and odds ratios, the confidence interval cannot contain:

Answer 30

1

Question 31

Sensitivity equation and table:

Answer 31

**TP/(TP+FN)** SNOUT

Question 32

Specificity equation and table:

Answer 32

**TN/(TN+FP)** SPIN

Question 33

Positive predictive value equation and table:

Answer 33

**TP/(TP+FP)**

Question 34

Negative predictive value equation and table:

Answer 34

**TN(TN+FN)**

Question 35

False positive rate =

Answer 35

1 - specificity

Question 36

Positive Likelihood Ratio equation:

Answer 36

**LR+ = Sn / (1-Sp)**

Question 37

Negative Likelihood Ratio equation:

Answer 37

**LR- = (1-Sn) / Sp**

Question 38

Odds ratio definition and table:

Answer 38

* retrospective * start with people who have disease, and go backwards to find risk factor

Question 39

The probability of two mutually exclusive events, A or B, occurring =

Answer 39

**(probability A) + (probability B)**

Question 40

Relative risk definition and table:

Answer 40

* prospective; follow * start with the risk factor, follow them over time, see how many people get disease * everyone starts with no disease

Question 41

Probability:

Answer 41

* a proportion in which the frequency of both events are in the denominator: ## Footnote **A/(A+B)**

Question 42

The probability of two independent events, A and B, occurring together =

Answer 42

**(probability A) X (probability B)**

Question 43

Absolute risk definition and table:

Answer 43

* attributable risk * a difference of relative risks * how much of getting the disease is attributable to having the risk factor

Question 44

Number needed to treat (NNT) equation and table:

Answer 44

* takes everyone into account * NNT = 1/ARR

Question 45

Absolute risk reduction equation and table:

Answer 45

Question 46

Number Needed to Harm (NNH) equation:

Answer 46

1/AR