r.squared(object, model = NULL, type = c("cor", "rss", "ess"), dfcor = FALSE)"plm",NULL, the transformation used to estimate the
model is also used for the computation of R squared,"rss" (residual sum of squares),
"ess" (explained sum of squares), or
"cor" (coefficient of correlation between the fitted values and the
response),TRUE, the adjusted R squared is computed.