STATS 7 ANALYSIS OF A SCALE Flashcards
Why are psychological constructs difficult to measure?
difficult to know what the level of measurement of the attribute should be e.g. continuum vs categorical
What is measurement by fiat?
Arbitrary assignment of numbers to responses
How are numbers assigned in Likert scales?
By fiat!
How are numbers assigned in Judgement scaling?
Empirically, by basing scale numbers off of initial research
What is item difficulty?
Item difficulty refers to the item mean, the higher the mean the easier the item
What is the floor effect?
When everyone fails, test is too hard
What is the ceiling effect?
When everyone passes, test is too easy
So, do we just want medium item difficulty across all items in a psychometric test?
No! Easy items are needed to differentiate between people at low levels of the attribute, difficult items are needed to differentiate between people at high levels of the attribute
How is the observed test score derived from the item scores in psychometric tests?
Test score is either derived from the sum of the item scores or the weighted sum of the item scores
What does a positive skew in the psychometric test distribution show?
Floor effect - test is too difficult
What does a negative skew in the psychometric test distribution show?
Ceiling effect - test is too easy
What is a raw score in psychometric scales?
The test score (sum or weighted sum of item scores)
How do we interpret the observed test score in relation to a criterion?
Criterion - pre-defined standard of behaviour - does not relate the observed test score to the other scores in the population of interest, origin 0 unit 1
How do we interpret the observed test score in relation to a norm?
Norm - reference to a distribution of scores in the population of interest - origin is the mean and unit is a standard deviation
