A Multi-Index Reliability Examination of the ISPTEQ Instrument among Private Secondary School Teachers in Gusau, Zamfara State, Nigeria
DOI:
https://doi.org/10.64348/zije.2026428Abstract
Scale reliability is a necessary condition for valid score interpretation. Yet, most educational research conducted in Nigerian private schools reports only Cronbach's alpha, thereby neglecting complementary indices that reveal distinct facets of measurement consistency. The present study systematically evaluated the psychometric reliability of the three-subscale ISPTEQ instrument (N = 386 teachers) using five independent reliability indices: Cronbach's alpha with Feldt, Woodruff, and Salih (1987) 95% confidence intervals; McDonald's omega-hierarchical; Spearman–Brown corrected split-half reliability; item-total discrimination coefficients; and item difficulty proportions. Alpha values were: S1 = .724 (95% CI [.679, .760]), S2 = .621 (95% CI [.560, .671]), and S3 = .620 (95% CI [.558, .671]). McDonald's omega was uniformly lower than alpha (S1 = .652; S2 = .522; S3 = .502), indicating that alpha systematically overestimates reliability when the essential tau-equivalence assumption is violated. Spearman–Brown values were S1 = .725, S2 = .613, and S3 = .644. Mean inter-item correlations fell below the .15 target for all three scales (ISPS: .127; TES: .093; TQS: .119), and 67–88% of item pairs did not attain r = .15. No item exceeded a discrimination index of .36. Item difficulty proportions ranged from .78 to .84, confirming a systematic ceiling effect. Collectively, the multi-index profile characterises the instrument's reliability as marginally acceptable for research purposes but in need of targeted item revision. These findings highlight the limitations of relying solely on Cronbach's alpha and provide a roadmap for strengthening the ISPTEQ instrument in future research.
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