Birth order is a factor. You can't have a fractional birth order - e.g. ORDER = 1.5 makes no sense. You are either first, second, third, etc. "Order" in your data can only take two unique values, and thus anything plotted against birth order is only going to vary along a vertical line above permitted values of birth order. -- View this message in context: http://r.789695.n4.nabble.com/How-to-make-a-scatter-plot-tp4685675p4685678.html Sent from the R help mailing list archive at Nabble.com.