Construct validity and reliability of a test for sacroiliac dysfunction: Downing test

Background: Low back pain is the main cause of global disability, with 13-30% of patients with low back pain reporting pain in the sacroiliac joint (SIJ). One of the clinical tests available for assessing SIJ mobility is the Downing test. However, information about the reliability and validity of this test is scarce in the scientific literature.Objectives: To evaluate the construct validity and intra and inter-rater reliability of the Downing test.Methods: Prospective study, in which the sample consisted of 30 individuals of both sexes. The evaluation team was composed of 5 researchers. The evaluations took place on two different days: (1st day) inter-rater reliability and construct validity; (2nd day) intra-rater reliability. The reference standard used for construct validity was three-dimensional measurements, using the BTS Smart-DX system. Statistical analysis: the percentage (%) agreement and the kappa statistic (k) were used.Results: Moderate agreement was found for construct validity for the conclusion of the test (% agreement = 54.5%; k = 0.43; p < 0.01) and intra-rater reliability (% agreement = 66.7%; k = 0.43; p < 0.01). However, agreement was poor for inter-rater reliability (% agreement = 16.7%; k = 0.15; p < 0.05).Conclusions: The construct validity of the Downing test was confirmed, only for the conclusion of the test, and it is reliable when applied by the same rater to healthy people, even if the rater has only 2 years of experience. The test is unreliable when it is performed by different raters. We suggest further studies that investigate the measurement properties of the Downing test, especially in symptomatic patients.