What is a key characteristic of alternative and parallel forms of reliability?

The correct choice emphasizes that alternative and parallel forms of reliability involve two different versions or forms of a test, which are designed to measure the same underlying construct. The key characteristic is that these forms must correlate with each other to establish that they are measuring the same thing consistently. High correlation indicates that the two forms yield similar results, which supports the reliability of the measurements taken from both.

This correlation is essential for confirming that despite the different questions or items, the tests are interchangeable in terms of their ability to capture the construct being assessed. Therefore, the focus on correlation highlights the need for consistency across different formats or versions of a test in ensuring reliable assessment outcomes.