11 Assessing Validity and Reliability Flashcards Preview

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Flashcards in 11 Assessing Validity and Reliability Deck (23)
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1

Reliability

The degree of stability exhibited when a measurement is repeated under identical conditions
If you do something over and over again, will you get the same result?

2

Validity

A measurement
An expression of the degree to which a measurement measures what it is trying to measure

3

Precision and accuracy
1. Gold standard
2. Silver standard
3. Off-base model
4. Hit or miss model

1. Both
2. Good accuracy, poor precision
3. Good precision, poor accuracy
4. Poor both

4

Screen versus diagnose

Screen: no preset notion of having a disease (it is done in an apparently healthy population - applying a test to a general population)
Diagnose: trying to find a disease in a particular person

5

Screening definition

The identification of unrecognized disease or defect through application of tests, examinations or other procedures in apparently healthy people
No concern in that person about the disease being screened for
No diagnostic intent
Very low to low disease prevalence

6

Diagnosis definition

Confirmation of presence or absence of disease in someone who is suspected of having it
People with symptoms of disease
Diagnostic intent
Low to high disease prevalence

7

In order to have a screening program, what is necessary?

A pre-clinical phase

8

Primordial prevention

Alter societal structures and thereby underlying determinants
Preventing the risk factors themselves

9

Primary prevention

Alter exposures that lead to disease
Prevent the disease from occurring

10

Secondary prevention

Detect and treat pathological process at an earlier stage when treatment can be more effective
Prevent symptomatic manifestation
Screening is here

11

Tertiary prevention

Prevent relapses and further deterioration via follow up care and rehabilitation
Attempt to minimize the adverse impact of the diseases

12

How do we decide if a screening program is worthwhile?

Disease must be important
Early treatment must be better than late
Prevalence of preclinical disease has to be high enough to justify costs
Simple to administer
Those being screened should be likely to comply
Should provide a true measure
Reproducible results
Cost-effective

13

Sensitivity

The test correctly identifying those who have the disease
True positive rate
a/(a+c)

14

Specificity

The test is negative in those who do not have the disease
True negative rate
d/(b+d)

15

Positive predictive value

Percentage of correct results in those with a positive test result
a/(a+b)
True positives / (true positives + false positives)

16

Negative predictive value

Percentage of true negative results in those with a negative test result
d/(d + c)
True negatives/ (true negatives + false negatives)

17

Pre-test probability

Same as the prevalence, but applied to an individual

18

Post-test probability measurements

The probability of the disease in an individual after a given test result

19

Lead-time bias

Apparent increased survival duration because of screening
Screen detected cases survive longer without benefit of early treatment (no prolongation of life)

20

Selection bias

Volunteers or compliers are better educated and more health conscious, thus they they have a better prognosis

21

Length-time bias

Screening preferentially identifies slower growing or less progressive cases that have a better prognosis
At one point in time, more people are likely to have slow growing cancers compared to aggressive cancers

22

Overdiagnosis bias

Too many false positives

23

How can we properly evaluate if a screening diagnostic program or test is effective?

Randomized control trial