zinterval(x[,y],cover:fraction,var:variance,[upper:T or lower:T]) |
zinterval() computes a z-confidence interval for a population mean or difference of population means, depending on whether one or two variables are given as arguments. By default, zinterval() computes a two-sided interval, but you may choose one-sided alternatives by using one of lowerb:T or upperb:T. You specify the coverage rate via cover:value. You specify the variance via var:variance. For a two-sample interval, you may specify different variances by using a vector of length two. The output is a vector containing the estimate and interval bounds. Because the variance of the data must be known, these intervals are rarely used in practical data analysis.