Final answer:
Split-half reliability should be avoided for a heterogeneous test.
Step-by-step explanation:
When dealing with a heterogeneous test, the estimate of reliability that should be avoided is Split-half reliability. Split-half reliability involves dividing the test into two halves and comparing the scores to estimate the test's reliability. However, this method may not be appropriate for a heterogeneous test because the two halves may not accurately represent the full range of difficulty and content.
On the other hand, Cronbach's alpha, test-retest reliability, and inter-rater reliability are more appropriate for assessing the reliability of a heterogeneous test.