Flashcards in Critical Appraisal and Statistics Deck (13):

1

## Define the mean, mode and median

###
– Mean is the average

– Median is the “middle” number(s)

– Mode is the most frequent number

2

## Define variance

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– “averaged (squared) distance of data from the center”

– The sum, from 1 to n, of (xi – x)2 / (n-1)

3

## What is standard deviation and how do you calculate it?

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– a quantity calculated to indicate the extent of deviation for a group as a whole

– The square root of the variance

4

## What is the standard error of the mean and how do you calculate it?

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– changes with sample sizes, gets more accurate as our data sample gets bigger

– The standard deviation divided by the square root of n

5

## Define a p-value

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the probability of an observed (or extreme) result arising just by chance

it is not synonymous with significance, of more importance is the confidence interval and effect size

6

##
How do you calculate sensitivity? What does it mean?

(use letters re: 2x2 table)

###
a/(a+c)

rule in

7

##
How do you calculate specificity? What does it mean?

(use letters re: 2x2 table)

###
d/(b+d)

rule out

8

##
How do you calculate positive predictive value? What does it mean?

(use letters re: 2x2 table)

###
a/ (a+b)

Positive predictive value is the probability that subjects with a positive screening test truly have the disease

9

##
How do you calculate negative predictive value? What does it mean?

(use letters re: 2x2 table)

###
d/(c+d)

Negative predictive value is the probability that subjects with a negative screening test truly don't have the disease.

10

## What is probability?

###
It is essentially the same thing as prevalence or chance.

= total with disease in question over the population

11

## What is the odds?

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It considers the chances for vs the chances against.

Calculate it by

probability/ (1-probability)

12

## How do you calculate the odds ratio?

### OR = Odds at risk/ Odds not at risk

13