Sample Size : Power : Confidence Interval : Pilot Study :

Data Input for Sample Size : is a table of 6 columns

• Each row contains data from a separate study
• Col 1 = Probability of Type I Error α
• Col 2 = Power (1 - β)
• Col 3 = number of items in Alpha₁ (k1)(questions in a factor)
• Col 4 = Cronbach Alpha₁ expected (CA1)
• Col 5 = number of items in Alpha₂ (k2)(questions in a factor)
• Col 6 = Cronbach Alpha₂ expected (CA2)

Data Input for Power Estimation : is a table of 6 columns

• Each row contains data from a separate study
• Col 1 = Probability of Type I Error α
• Col 2 = Averaged sample size per Alpha (assuming equal size groups) ((n1+n2)/2)
• Col 3 = number of items in Alpha₁ (K1)
• Col 4 = Cronbach Alpha₁ observed (CA1)
• Col 5 = number of items in Alpha₂ (K2)
• Col 6 = Cronbach Alpha₂ observed (CA2)

Data Input for Confidence Interval : is a table of 6 columns

• Each row contains data from a separate study
• Col 1 = Percent confidence (usually 95 or 99)
• Col 2 = Sample size per Alpha (assuming equal size groups) ((n1+n2)/2)
• Col 3 = number of items in Alpha₁ (K1)
• Col 5 = number of items in Alpha₂ (K2)
• Col 6 = Cronbach Alpha₂ observed (CA2)

Data Input for Pilot Stury : is for a single plan, a single column with 7 rows

• Row 1 : Percent confidence required, usually 95 or 99
• Row 2 : Number of items in the first Alpha (k1)
• Row 3 : Value of the first Alpha Coefficient (CA1)
• Row 4 : Number of items in the second Alpha (k2)
• Row 5 : Value of the second Alpha Coefficient (CA2)
• Row 6 : Sample size interval for tabulation of changing width of the confidence interval. This is usually established by trial and error, starting at about 5
• Row 7 : Maximum sample size (per Alpha) for tabulation of changing width of the confidence interval. This is usually established by trial and error. For most clinical studies however, the sample size is between 10 and 200, and this range can be used as starting levels

Bonett D G (2002) Sample Size Requirements for Comparing Two Alpha Coefficients Applied Psychological Measurement, Vol. 27 No. 1, January 2003, 72 - 74

Duhachek A and Iacobucci D (2004) Alpha's Standard Error (ASE): An Accurate and Precise Confidence Interval Estimate. Journal of Applied Psychology Vol. 89, No. 5, 792-808

Johanson GA and Brooks GP (2010) Initial Scale Development: Sample Size for Pilot Studies. Educational and Psychological Measurement Vol.70,Iss.3;p.394-400