ggplot2 draws two legends
I have almost complete the following graph, but there is one problem with it. The legend in the graph is drawn twice. Here is the data: structure(list(Period = c("January 1997 - August 2003", "September 2003 - Jun 2005", "Jul 2005 - Dec 2009", "January 1997 - August 2003", "September 2003 - Jun 2005", "Jul 2005 - Dec 2009"), Time.Period = structure(c(1L, 3L, 2L, 1L, 3L, 2L), .Label = c("Jan 1997 - Aug 2003", "Jul 2005 - Dec 2009", "Sep 2003 - Jun 2005"), class = "factor"), Variable = structure(c(2L, 2L, 2L, 1L, 1L, 1L), .Label = c("Significant", "Zscore"), class = "factor"), Score = c(8.798129