This is yet another of the unavoidable trade-offs in measurement. In designing a test of a large domain such as fourth-grade mathematics, one would want reasonably broad coverage of the domain to support the conclusions in which you are interested, but that breadth of content will reduce reliability. As the reliability coefficients above suggest, with careful work, the authors of tests of broad domains can in fact attain high levels of internal consistency reliability, but this is nonetheless constrained by the breadth of the test. One of the most important influences on reliability is the
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