Median Polish of a Matrix

Usage

medpolish(x, eps=0.01, maxiter=10, trace.iter = TRUE)

plot(medpolish.obj)
print(medpolish.obj)

Description

medpolish fits an additive "two-way" (constant + rows + columns) model to the values given in x using Tukey's median polish procedure.

Details

Sweeping out for row and column effects continues until the proportional reduction in the sum of absolute residuals is less than eps or until there have been maxiter iterations. The sum of absolute residuals is printed at each iteration of the fitting process, if trace.iter is TRUE.

medpolish returns an object of class medpolish (see below). There are printing and plotting methods for this class, which are invoked via by the generics print and plot.

Value

An object of class medpolish with the following named components:
overall the fitted constant term.
row the fitted row effects.
col the fitted column effects.
residuals the residuals.
name the name of the dataset.

References

Tukey (1977). E.D.A; see ref. in line.

See Also

median; aov which for a mean instead of median decomposition.

Examples

## Deaths from sport parachuting;  from ABC of EDA, p.224:
deaths <-
    rbind(c(14,15,14),
          c( 7, 4, 7),
          c( 8, 2,10),
          c(15, 9,10),
          c( 0, 2, 0))
dimnames(deaths) <- list(c("1-24", "25-74", "75-199", "200++", "NA"),
                         paste(1973:1975))
deaths
(med.d <- medpolish(deaths))
plot(med.d)
## Check decomposition:
all(deaths == med.d$overall + outer(med.d$row,med.d$col, "+") + med.d$resid)

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