What is Reliability?
You can think about reliability in terms of consistency of scores. If you test a student today and test a student tomorrow, are the scores going to be similar? If you test one population of students and a different population of students, are you going to see similar scores on the same assessment? In terms of internal reliability, if you’re administering the first part of the assessment to students, and then the second part of the assessment, are the scores on the first part and second part going to be similar? These questions deal with the issue of whether students are performing on all of the items within a given assessment consistently.
What is Validity?
In a nutshell, test validity is whether any given assessment measures what it’s supposed to measure. What we’re often trying to ascertain is content validity and criterion validity.
When we have item writers creating any given item, we’re trying to make sure that the items are aligned to certain standards. In order to do this, we need multiple people making sure that the item aligns to certain standards or that the assessment as a whole aligns to a given number of standards. So, having three people blindly aligning items or assessments to the standards is having content validity.
On top of that, once the assessment is in production, what I do is criterion validity. How good of a predictor that assessment is to any other given instrument or assessment (e.g., end-of-year state assessment). So, in order to do that, we correlate performance on any given assessment or benchmark, any Inspect assessment with state test performance, or any other valid instrument like ACT or SAT.
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