Calculating Sample Size in R (Means)

Below is a video tutorial showing how to calculate the sample size for tests on a mean.  This shows how to conduct both single-sample and two-sample tests as well as single-sided and two-sided tests.  Below the video is the syntax used in the video.

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###  Determining sample size in R.

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###  Testing Ho: mu = 15

###          Ha: mu > 15

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###  Power power = 0.9

###  Population stdev stdv = 2.32

###  Difference delta = 2.5

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###  Significance level sig.level = 0.01

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power.t.test( power = 0.9,               # Power

              delta = 2.5,               # Difference between mu and xbar

              sd = 2.32,                 # Standard Deviation

              sig.level = 0.01,          # Significance level

              type = "one.sample",       # Type of study

              alternative = "one.sided"  # Type of test

             )

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###  For a two sided two sample test.

###  Testing Ho: mu1 = mu2

###          Ha: mu1 <> mu2

power.t.test( power = 0.95,              # Power

              delta = 1.6,               # mu1 - mu2

              sd = 2.14,                 # Standard Deviation

              sig.level = 0.02,          # Significance level

              type = "two.sample",       # Type of study

              alternative = "two.sided"  # Type of test

             )