In addition, when reviewing this data, we need to also be familiar with two basic measurement concepts. Firstly, validity, which refers to the appropriateness, meaningfulness, and usefulness of the specific inferences made from test scores. It may not be appropriate, for example, to make inferences about the quality of an instructional program solely on the base of test scores. There are many other factors that influence test results, such as the general intellectual level of students, the extent to which they are motivated to learn and to obtain high scores, the availability of community resources, such as museums and libraries, etc. The second measurement concept is reliability.
Reliability refers to the degree to which a test is error-free.
Although test scores may have an air of mathematical precision about them, none is error-free. Group size is also an extremely important consideration in the evaluation of changes in a school or school district's results from one year to the next, and in comparison between schools and school districts. When the number of students tested is small, the differences may not be significant, either statistically or practically. Thus, a test given annually in third and sixth grade evaluates an entirely different student population with its own abilities, attitudes, and pre-occupations each year.