Test reliability

Test reliability is the repeatability or consistency of a test’s results.^{1Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 192.} If a client’s ability hasn’t changed, a perfectly reliable test gives the same score each time; any difference is measurement error.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 267.},^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 268.} Test-retest reliability is checked by repeating a test on the same people under the same conditions, without training or diet changes between tests, within one to three days or up to a week for strenuous tests.^{1Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 192.},^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 268.}

Intrarater reliability describes whether one trainer gets the same result from session to session.^{1Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 192.} Interrater reliability, also called objectivity, describes whether different trainers get the same result from the same client.^{1Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 192.} Reliability is required for test validity, because highly variable results have little meaning.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 267.}

In practice

• Practice the assessment protocol: good published reliability is meaningless unless the trainer uses strict, standardized conditions.^{1Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 192.}
• Use the same scorer before and after training; a lenient pretest scorer and strict posttest scorer can hide real improvement.^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 268.}
• ACSM recommends keeping the test order the same at later sessions.^{4Ozemek et al., ACSM’s Guidelines for Exercise Testing and Prescription, 12th ed., p. 169.} ISSA recommends measuring at the same time of day, noting that arms measured cold in the morning differ from arms measured pumped after a high-volume workout.^{5International Sports Sciences Association, Bodybuilding: The Complete Guide to Unlocking Muscle Hypertrophy, 1st ed., p. 163.}
• Between-rater variability in skinfold body fat measurements can run 3% to 9%, and the NSCA puts proficiency at about 100 practice opportunities.^{6Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 194.} Technique-intensive tests vary more and need more practice.^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 268.}