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Revision 3 as of 2007-06-08 10:30:12

location: FAQ / points

= How do I scatterplot observations which have the same set of co-ordinates?=

Sometimes the same co-ordinates are shared by more than one observation. A scatterplot will only, however, show one point for each unique x,y combination regardless of the number of observations that share this combination.

One way of disentangling this is to add a proportionately small amount to the observed values of one of the variables, say, y. The below syntax uses the rv.uniform function in SPSS to add a small random amount to the y values. The new values which are now all unique (ynew) can then be plotted against x.

COMPUTE YNEW = Y + RV.UNIFORM(Y*0.01,Y*0.015).