Allan's main advice is to fit a regression line with
an outlier and to show it on a graph together
with all the other data.
That's often a useful technique, but I read
Timothy's discussion of line plots as wanting
something quite different, namely
* outlier off graph
/ \
/ \
/ \ lines on graph pointing to it
I am sure that this is programmable, but I don't know an
easy and general way for a user to do it.
Likewise Allan's other suggestions do not seem to bear
on this problem.
Nick
[email protected]
Allan Reese (Cefas)
> Hate to disagree with Nick, but Stata is well-designed for
> intelligent graph editing. Timothy maybe needs to fiddle
> with a few alternatives and work out what would show what he
> intends. A log scale is one option but has many other implications.
>
> For example, it's straightforward in Stata to draw lines
> with/without outliers. Other "point'n'click" packages don't
> make this easy, so suppress the desire.
>
> fit y x
> predict yhat1
> fit y x if y<1000
> predict yhat2
> scatter y yhat1 yhat2 x if y<1000, connect(. l l) msym(o i i) sort
>
> Another simple trick is to copy one variable into several, so
> subsets can be distinguished on the plot. You could automate
> this (eg, using egen to save the max value of x), but I'd
> usually do it as part of visual editing, for example to add
> text labels to the points at the end of each line. It's
> therefore feasible to draw a line for the data excluding the
> outlier, and add a second line in different style pointing up
> with a label at its end describing the outlier.
>
> This is the type of work where I'd draft commands in a DO
> file so they are easily modified and re-run.
Nick Cox
> What you want is _not_ straightforward. I know no easy and also
> general way of omitting a data point from a Stata graph and also
> having it exert some offstage influence on the remainder of
> the graph.
>
> In my experience, when people think they want something like
> this using a logarithmic scale for the variable concerned is
> usually the
> best way forward.
Timothy Dang
> > I'm making a lot of (line) plots in Stata, and mostly it's working
> > great, but I've hit a snag. For a few of my data sets,
> there are some
> > data points which are extraordinarily high. With the automatically
> > scaled axis ranges, these points are visible, but all the detail of
> > the rest of the data is shrunk to invisibility.
> >
> > So, I want to:
> > (a) enforce a maximum for the axis, hopefully showing the
> lines going
> > up towards some point not shown on the plot, and
> > (b) add some text describing what happens at those points (I can do
> > this outside Stata if needed).
> >
> > Hopefully this is straightforward and I've just missed something.
> > Thanks for any pointers.
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