reliability and validity of measurements sv

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Reliability and Validityof Measurements


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Definitions

Reliability-consistent,reproducib

le,dependable

Validity-measureswhat it

says itmeasures


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Measurement Error

Reliability Coefficients

Types of Reliability

Reliability


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Measurement Error

Observed score = true score + error

Measurement Error = true score observed score

Reliability estimates measurement error


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Sources of MeasurementError

Systematic- consistently wrong in thesame amount

Random- chance

rater

measuring instrument variability in what you are measuring


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Reliability Coefficients

True score variance

True score variance + error variance

as error increases, coefficient increases

coefficient ranges from .00 to 1.00

< .50 poor

.50 to .75 moderate

> .75 good


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Types of Reliability:Test-Retest

Get the same results every time you usethe test

Intervals between testing- long enough

to avoid fatigue or remembering theanswers but not so long that naturalmaturation occurs

Intraclass correlation coefficient (ICC)


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Another way to Test- Retest

Alternate forms: different versionscovering the same content (SAT, GRE)

correlation coefficient is used


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Types of Reliability: InternalConsistency

Are all questions measuring the samething?

Split-half: correlation of two halves of

same test (odds and evens) Spearman-Brown prophecy

Cronbachs alpha: essentially an averageof the all the possible split-halfreliabilities, can be used on multiple

choice.


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Types of Reliability: Raters

Intra rater: stability of one rater acrosstrials

Inter-rater: consistency between tworaters

UseICC

forbothtypes


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Validity vs. Reliability

Types of Validity

Validity


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Validity vs. Reliability


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Generalizability

External validity- the test is valid if usedwith the intended population

The test is reliable if used in appropriate

context and as directed for its givenpurpose


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Face Validity

appears to test what it is supposed tomeasure

weakest form

ok for ROM, length, observation of ADLs


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Content Validity

covers the entire range of the variableand reflects the relative importance ofeach part

based on expert opinion, needs to free ofcultural bias

Test of function- 20 questions on

brushing your teeth, 1 question each onmobility, bathing, dressing

VAS vs. McGill Pain Questionnaire


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Criterion-related Validity

target test istaken at the sametime as anothertest withestablishedvalidity

examineswhether thetarget test canpredict a criterionvariable

concurrent predictive

target test compared to goldstandard


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Construct Validity

ability of a test to measure a construct

based on a theoretical framework

what would you include for a test onwellness?


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Ways to establish constructvalidity

Known groups

Convergent comparison

Divergent comparison Factor analysis


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Remember

The reliability and validity of a testmeasurement is not the same thing asreliability and validity of a research

design.

reliability and validity of measurements sv

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