ggplot2：用箭头显示值随时间的差异

I have a data set with scores to questions asked over two years. Each question has a 2015 value and a 2016 value. I would like to plot each and then show the different between the 2015 value and the 2016 value. Did the score go up or down or stay the same? I was thinking it might be useful to connect pairs of points with a line (or an arrow) to show the direction of change, but I'm having a hard time getting ggplot to do this. Here is my code example:I have a data set with scores to questions aske