STUDY DESIGN: Inter-rater chance-corrected agreement study. OBJECTIVE: The aim was to examine the association between therapists' level of formal precredential McKenzie postgraduate training and agreement on the following McKenzie classification variables for patients with low back pain: main McKenzie syndromes, presence of lateral shift, derangement reducibility, directional preference, and centralization. SUMMARY OF BACKGROUND DATA: Minimal level of McKenzie postgraduate training needed to achieve acceptable agreement of McKenzie classification system is unknown. METHODS: Raters (N = 47) completed multiple sets of 2 independent successive examinations at 3 different stages of McKenzie postgraduate training (levels parts A and B, part C, and part D). Agreement was assessed with κ coefficients and associated 95% confidence intervals. A minimum κ threshold of 0.60 was used as a predetermined criterion for level of agreement acceptable for clinical use. RESULTS: Raters examined 1662 patients (mean age = 51 ± 15; range, 18-91; females, 57%). Data distributions were not even and were highly skewed for all classification variables. No training level studied had acceptable agreement for any McKenzie classification variable. Agreements for all levels of McKenzie postgraduate training were higher than expected by chance for most of the classification variables except parts A and B training level for judging lateral shift and centralization and part D training level for judging reducibility. Agreement between training levels parts A and B, part C, and part D were similar with overlapping 95% confidence intervals. CONCLUSION: Results indicate that level of inter-rater chance-corrected agreement of McKenzie classification system was not acceptable for therapists at any level of formal McKenzie postgraduate training. This finding raises concerns about the clinical utility of the McKenzie classification system at these training levels. Additional studies are needed to assess agreement levels for therapists who receive additional training or experience at the McKenzie credentialed or diploma levels. LEVEL OF EVIDENCE: 2.
