ss.ci: Confidence Interval for the mean In SixSigma: Six Sigma Tools for Quality Control and Improvement

Description

Computes a confidence interval for the mean of the variable (parameter or feature of the process), and prints the data, a histogram with a density line, the result of the Shapiro-Wilks normality test and a quantile-quantile plot.

Usage

 1 2 3 4 ss.ci(x, sigma2 = NA, alpha = 0.05, data = NA, xname = "x", approx.z = FALSE, main = "Confidence Interval for the Mean", digits = 3, sub = "", ss.col = c("#666666", "#BBBBBB", "#CCCCCC", "#DDDDDD", "#EEEEEE")) 

Arguments

 x A numeric vector with the variable data sigma2 The population variance, if known alpha The eqn\alpha error used to compute the 100*(1-\α)\% confidence interval data The data frame containing the vector xname The name of the variable to be shown in the graph approx.z If TRUE it uses z statistic instead of t when sigma is unknown and sample size is greater than 30. The default is FALSE, change only if you want to compare with results obtained with the old-fashioned method mentioned in some books. main The main title for the graph digits Significant digits for output sub The subtitle for the graph (recommended: six sigma project name) ss.col A vector with colors

Details

When the population variance is known, or the size is greater than 30, it uses z statistic. Otherwise, it is uses t statistic.
If the sample size is lower than 30, a warning is displayed so as to verify normality.

Value

The confidence Interval.
A graph with the figures, the Shapiro-Wilks test, and a histogram.

Note

Thanks to the kind comments and suggestions from the anonymous reviewer of a tentative article.

EL Cano

References

Cano, Emilio L., Moguerza, Javier M. and Redchuk, Andres. 2012. Six Sigma with R. Statistical Engineering for Process Improvement, Use R!, vol. 36. Springer, New York. http://www.springer.com/statistics/book/978-1-4614-3651-5.

ss.data.rr

Examples

 1 2 3 ss.ci(len, data=ss.data.strings, alpha = 0.05, sub = "Guitar Strings Test | String Length", xname = "Length") 

Example output

	Mean = 950.016; sd = 0.267
95% Confidence Interval= 949.967 to 950.064

LL       UL
949.9674 950.0640


SixSigma documentation built on April 16, 2018, 1:03 a.m.