Module 6: Reliability and Validity Flashcards
Reliability
Reliability refers to the consistency or stability of a measuring instrument. In other words, the measuring instrument must measure exactly the same way every time it is used.
Systematic errors
Problems that stem from the experimenter and the testing situation.
Trait errors
Problems that stem from the participants. Were they truthfull, did they feel well?
True score
The true score is what the score on the measuring instrument would be if there were no error.
Error score
The error score is any measurement error (systematic or trait).
Observed score
The score recorded for a participant on the measuring instrument used.
Conceptual formula for observed score
Observed score = True score + Error score
Random errors
Errors in measurement that lead to measurable values being inconsistent when repeated measurements of a constant attribute or quantity are taken
Conceptual formula for reliability
Reliability = True score / (true score + error score)
Correlation coefficients
A correlation coefficient measures the degree of relationship between two sets of scores and can vary between -1.00 and +1.00. The stronger the relationship between the variables, the closer the coefficient is to either 1.00 or +1.00.
Positive correlation
A positive correlation indicates a direct relationship between variables: When we see high scores on one variable, we tend to see high scores on the other
Graph going from left bottom to right top
Negative correlation
A negative correlation indicates an inverse, or negative, relationship: High scores on one variable go with low scores on the other and vice versa.
Graph going from left top to right bottom
Rules-of-thumb correlation coefficient
.29 = none to weak .30-.69 = moderate .70-1.00 = strong
Types of reliability
- Test/retest
- Alternate forms
- Split-half
- Interrater reliability
Test/retest reliability
One of the most often used and obvious ways of establishing reliability is to repeat the same test on a second occasion. The correlation coefficient needs to be high on both tests for the reliability to increase as well.