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# y versus x, or x versus y? [was: Re: st: quantile-quantile plots]

 From Nick Cox To "statalist@hsphsun2.harvard.edu" Subject y versus x, or x versus y? [was: Re: st: quantile-quantile plots] Date Tue, 16 Apr 2013 09:54:53 +0100

```Very interesting example; thanks for thinking about my question.

I studied economics when young. I can't recollect if I was puzzled
then that demand curves (your example) and supply curves were plotted
with price on the vertical axis. But it also seems fair to regard
price as the outcome or response that is being explained here, namely
that price arises out of the interaction of supply and demand, just as
much as the other way around. So on that argument this kind of diagram
is not an exception.

No doubt all the real economists and econometricians will correct me
if I am wrong.

I must look in the book reviewed in http://ejpe.org/pdf/4-2-br-6.pdf

That review in turn yields a reference to broaden the horizons of all
inequality-measuring economists and social scientists:

Derobert, Laurent, and Thieriot, Guillaume. 2003. The Lorenz curve as
an archetype: a
historico-epistemological study. The European Journal of the History of Economic
Thought, 10 (4): 573-585.

But in terms of my original question, the language usages

plot y versus x

plot x versus y

-- and whatever logic lies behind them -- it strikes me now hat a
simpler explanation is just the algebraic convention of naming x
coordinate first, as in "its coordinates are (x, y)", so there is
merely a clash of conventions here.

Nick
njcoxstata@gmail.com

On 16 April 2013 04:07, Yu Chen, PhD <profyuchen@gmail.com> wrote:

> In economics, sometimes the vertical axis is used to plot independent
> variable, and the horizontal axis is used to plot the dependent
> variable. For example, when price goes up, you may buy less food.
> Price is plotted in vertical axis, and the quantity of food is plotted
> in horizontal axis. The curve is downward sloping. That might be the
> reason that you heard people saying plot x versus y.

On Mon, Apr 15, 2013 at 5:21 AM, Nick Cox <njcoxstata@gmail.com> wrote:

>> * A note on "versus" or "against". I was brought up -- probably in
>> school physics, but it was last century, so I can't give precise
>> recollections -- to say "plot y versus x" where y is, not
>> surprisingly, whatever is plotted on the y or vertical axis. That
>> seems to me to match mathematics and physics usages such as y is a
>> function of x, or output is a function of time, where the dependent
>> variable (outcome, response) is always mentioned first. But I've come
>> across people saying "plot x versus y". If anyone has a logic for that
>> usage, I'd be interested to hear it.
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