A researcher administers a newly developed questionnaire measuring a stable personality trait to a group of participants on two separate occasions, a week apart. They then calculate the statistical coefficient between the two sets of scores to evaluate consistency over time. What is this coefficient called, and what value would generally indicate that the questionnaire has good reliability?

If a researcher calculates a test-retest correlation of +.85 for a questionnaire measuring a stable trait, this statistical coefficient indicates that the measurement tool has demonstrated good reliability across different administrations.