Precision, Accuracy, And Validity Precision:- a very precise measurement is a one that has nearly the same value each time it is measured. A scale measurement is more precise than a qualitative one. The more precise a measurement the greater the statistical power. Assessing precision: usually by S.D.of repeated measurements, also the Co.V. or correlation coefficient.

Precision is usually affected by random errors, there are 2 main sources of errors: Subjective:- subject variability due to intrinsic biological variability ex.: fluctuation in mood, B.Pr., heart rate… Objective : 1- Observer: hand-eye coordination 2- Instruments: due to fluctuating environmental factors such as temperature, background noise,…

Strategies For enhancing precision: Through decreasing random errors, and this is done by: 1- Standardizing the measurement method 2- Training & certifying the observer 3- Refining the instruments 4- Automating the instruments 5- Repetition: repeat the measurement & use the mean

Accuracy The accuracy of a variable is the degree to which it actually represents what it is intended to represent. Precision Accuracy Definition Best way to use threatened by The degree to which a variable has nearly the same value when measured several times. Comparison among repeated measures Random error( chance) subjective and objective The degree to which a variable actually represents what it is supposed to comparison with a reference standard systematic error (bias) subjective & objective

Accuracy is affected by systematic errors (bias) of two types: 1- Subjective: Co-operation, re-call, illiteracy… 2- Objective : -observer: conscious or un-conscious -Instruments: which are not calibrated recently. .

Strategies for enhancing accuracy: The same 1-4 strategies of precision and : 5- Making unobtrusive measures: design measurements that the observer is unaware of. 6- Blinding: Single, double, triple (the researcher or the manager who is reading the outcome) 7- Calibrating the instruments The discussion on how vigorously to peruse each of these strategies depends on feasibility and cost of the strategy

Validity Predictive Validity: the degree to which the measurement successfully predicts an outcome Criterion related Validity: the degree to which the measurement agrees with other approaches for measuring the same characteristics (ex. Question about stress) Face Validity: a subjective judgment whether a measurement makes sense intuitively, whether it seems to be a reasonable approach.