To increase credibility in a research study, retesting subjects helps ensure:

Retesting subjects in a research study is primarily aimed at enhancing reliability. Reliability refers to the consistency and stability of results over time and across different conditions. When subjects are retested, it allows researchers to verify that the findings are consistent, and not just due to chance or specific conditions present during the initial testing. This repeated measurement can help identify any variations in the data and ensure that the outcomes are replicable.

While precision, validity, and variation are also important aspects of research, they serve different purposes. Precision involves how close multiple measurements are to each other, validity concerns whether the research accurately measures what it is intended to measure, and variation relates to the differences observed within a data set. Retesting primarily contributes to bolstering the reliability of the study findings, ensuring that they can be trusted and dependably reproduced in future research.