Computes three parametric correlation coefficients for one X variable and the corresponding R squared for multiple X variables, and a regression equation for censored data.
cencorreg(y.var, cen.var, x.vars, LOG = TRUE, verbose = 2)The column of y (response variable) values plus detection limits.
The column of indicators, where 1 (or TRUE) indicates a detection limit in the y.var column, and 0 (or FALSE) indicates a detected value is in y.var.
One or more uncensored explanatory variable(s). See Details
Indicator of whether to compute the regression in the original y units, or on their logarithms. The default is to use the logarithms (LOG = TRUE). To compute in original units, specify the option LOG = FALSE (or LOG = 0).
default verbose=2, see details.
When x.vars is one variable, likelihood, rescaled likelihood and McFaddens correlation coefficient (R) are printed.
When x.vars is a data.frame of more than one variable, likelihood, rescaled likelihood and McFaddens coefficent of determination (R2) are printed.
Model coefficients (intercept and slopes), Chi-Squared statistic and p-value for the test that all slope coefficients equal zero (overall test), and model AIC and BIC are provided.
A Q-Q plot of model residuals with corresponding Shapiro-Francia W and p-value are plotted for evaluation of model distributional assumptions when verbose=2 (the default).
x.vars: If one x variable only, enter its name. If multiple x variables, enter the name of a data frame of columns of the x variables. Only columns used as X variables in the regression are allowed. Create this by x.frame <- data.frame (Temp, Flow, Time) for 3 variables (temperature, flow and time) used as teh X variables in the regression.
AIC and BIC are printed to help evaluate the <U+2018>best<U+2019> regression model.
The default is that the Y variable will be log transformed.
verbose option. Default is 2 which provides full output in the console and qqplots in a graphics window. A value of 1 only provides partial results in the console and no qqplots. A value of 0 provides no output; the returning computations will be stored in the specified object.
Helsel, D.R., 2011. Statistics for censored environmental data using Minitab and R, 2nd ed. John Wiley & Sons, USA, N.J.
Helsel, D.R., 2005. Nondetects and Data Analysis: Statistics for Censored Environmental Data, 1st ed. John Wiley and Sons, USA, N.J.
# NOT RUN {
data(Brumbaugh)
# One variable
cencorreg(Brumbaugh$Hg,Brumbaugh$HgCen,Brumbaugh$SedMeHg)
# More than one variable for demostration purposes
cencorreg(Brumbaugh$Hg,Brumbaugh$HgCen,Brumbaugh[,c("SedMeHg","PctWetland")])
# }
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