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

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

    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
  1. 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