Statistical power as a function of Cronbach alpha of instrument questionnaire items

Table 2 Statistical power of the pre-post test T _PP (18): σ _μ = 1

			k = 5		k = 10
Total N	Δ _PP	C _α	φ _PP	\({\tilde{\varphi}}_{\mathit{\mathsf{P}}\mathit{\mathsf{P}}}\)	φ _PP	\({\tilde{\varphi}}_{\mathit{\mathsf{P}}\mathit{\mathsf{P}}}\)
30	0.4	0.5	0.341	0.337	0.341	0.310
		0.6	0.475	0.459	0.475	0.458
		0.7	0.658	0.626	0.658	0.649
		0.8	0.873	0.849	0.873	0.830
		0.9	0.996	0.997	0.996	0.995
50	0.3	0.5	0.323	0.309	0.323	0.296
		0.6	0.451	0.424	0.451	0.433
		0.7	0.630	0.633	0.630	0.614
		0.8	0.851	0.849	0.851	0.844
		0.9	0.994	0.995	0.994	0.992

Note: Total N: total number of subjects; k: number of items; \({\varDelta}_{\mathit{\mathsf{P}}\mathit{\mathsf{P}}}={\delta}_{\mathit{\mathsf{P}}\mathit{\mathsf{P}}}/{\sigma}_{\mu }\); C _α: Cronbach alpha; φ _PP: theoretical power (20); \({\tilde{\varphi}}_{\mathit{\mathsf{P}}\mathit{\mathsf{P}}}\): simulation-based empirical power

ISSN: 1471-2288