Flashcards in Clinical measurement Deck (19)

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1

## Describe reference ranges

###
generally 2.5% to 97.5%

If normally distributed can be calculated by mean +/- 2(1.96)SD

Just because patient has value outwit the reference range doesn't necessarily make them unhealthy- 5% of normal population will be outwith the reference range

2

## What can measurement errors be due to?

###
lack of accuracy (calibration)

Lack of precision (repeatability)

3

## What is biological variability?

### differences between repeated measurements taken at different time points

4

## what are instrumental errors?

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imprecise instruments

inaccurate diagnostic test

questionnaire limitations

5

## What are respondent errors?

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misunderstanding

faulty recall

trying to appear healthy

6

## What are observer errors?

### mistakes, imprecision in measurement or misunderstanding of procedures

7

## What are data processing errors?

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coding of variables

copying in of data

programming errors

calculation errors

8

## What is the coefficient of variation?

###
often used in lab experiments

it measures the degree of variation associated with repeated measurements

CV = SD/mean X 100

9

## What are two ways of comparing two methods of measurement?

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scatter plot

bland-altman plot

10

## describe using a scatter plot to compare methods of measurement

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with the line of equality

gives an impression of how well the two methods agree

11

## Describe the use of a bland altman plot to compare methods of measurement

###
its better

plots the difference between the measurements against the sum or the average of the observations

the differences are quantified by estimating the bias

The SD of the differences allows a range to be determined in which we would expect 95% of the differences to lie

there should be no pattern inn the plot suggesting that bias or SD is changing as the measurement increases

12

## What is sensitivity?

### the probability of a true positive test result if the disease is present a/a+c

13

## What is specificity?

###
the probability of a true negative test result if the disease is not present

b/b+d

14

## How is PPV calculated?

### a/a+b

15

## how is NPV calculated?

### d/c+d

16

## How is prevalence calculated?

### a+c/a+b+c+d

17

## Describe the Receiving Operating Characteristic (ROC) curve

###
Used to establish the optimal cut-off of what we want to achieve from a test

Plot sensitivity (true pos rate) against 1-specificity (flash positive rate) on the x-axis for different cut-off points

18

## Describe NNT

###
The number you need to treat with the new treatment to achieve one more "success" than with the old treatment

NNT=1/P(success new)-P(success old)

19