Sample Size : Power : Confidence Interval : Pilot Study :

Data Input to Calculate Sample Size : is a table of 5 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 the group (questions in a factor)
• Col 4 = Cronbach Alpha required or anticipated
• Col 5 = Reference or hypothetical Cronbach Alpha, usually 0 for null hypothesis

Data Input to Estimate Power : is a table of 5 columns

• Each row contains data from a separate study
• Col 1 = Probability of Type I Error α
• Col 2 = Sample size used
• Col 3 = number of items in the group (questions in a factor)
• Col 4 = Cronbach Alpha found
• Col 5 = Reference or hypothetical Cronbach Alpha, usually 0 for null hypothesis

Data Input to Estimate Confidence Interval : is a table of 4 columns

• Each row contains data from a separate study
• Col 1 = Percent confidence (usually 95 or 99)
• Col 2 = Sample size used
• Col 3 = number of items in the group (questions in a factor)
• Col 4 = Cronbach Alpha found

Data Input for a Pilot Study: is for a single plan, a single column with 5 rows

• Row 1 : Percent confidence required, usually 95 or 99
• Row 2 : Number of items in the data
• Row 3 : Cronbach's Alpha to be detected
• Row 4 : 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 5 : Maximum sample size or 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 Testing and Estimating Coefficient Alpha Journal of Educational and Behavioral Statisitcs 27: 335-340

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