Dear List:

I cannot seem to find a way to plot my data correctly. I have a small data frame with 6 total variables (x_1 ... x_6).

I am trying to plot x_1 against x_2 and x_3.

I have tried

plot(x_2, x_1) #obviously works fine

plot(x_3, x_1, add=TRUE) # Does not work. I keep getting error messages. 

I would also like to add ablines to this plot.

I have experimented with a number of other plotting functions and I cannot seem to get this to work.

The data are student achievement data. I am trying to plot percentile ranks against scale scores for different grade levels. When plotted as such, they look like logistic curves. I am trying to show graphically the distance along x a student must grow simply to remain at the same percentile rank, y. 

Thanks.
 

Harold C. Doran
One Massachusetts Avenue, NW · Suite 700 
Washington, DC 20001-1431
202.336.7075


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