Gives count, mean, standard deviation, standard error of the mean, and confidence interval (default 95%).
summarySE(data = NULL, measurevar, groupvars = NULL,
na.rm = FALSE, conf.interval = 0.95, .drop = TRUE)
a data frame
the name of a column that contains the variable to be summariezed
a vector containing names of columns that contain grouping variables
a boolean that indicates whether to ignore NA's
the percent range of the confidence interval (default is 95%)
should combinations of variables that do not appear in the input data be preserved (FALSE) or dropped (TRUE, default)
a data frame with count, mean, standard deviation, standard error of the mean, and confidence interval (default 95%).
http://www.cookbook-r.com/Graphs/Plotting_means_and_error_bars_(ggplot2)