Graph to start at y-axis

[Jane Skinner]

Hi
I have been reproducing the following graph (from "Sample size of 12 per group rule of thumb for a pilot study" by Julious), which I suspect was created in Excel:

I used the following code:

clear
set obs 28
gen n=_n+2
gen precision=(invttail(2*n-2,0.025)*sqrt(2))/sqrt(n)
gen gain_precision=precision[_n-1]-precision[_n]
label variable n "Sample Size"
label variable gain_precision "Gain in Precision"
twoway connected gain_precision n, xlabel(4(1)30, labsize(vsmall)) ylabel(0(0.1)0.6)

And get this graph:

(The line at y=0.5 is an artefact of conversion.)

Is there any way that I can get the line to start at the y-axis like the original, rather than having the gap between the line and the y-axis?

Thanks,

Jane

[William Lisowski]

Because you have an observation with n=3, Stata extends the X axis to 3, even though gain_precision is missing in that observation and thus nothing is actually plotted at 3. The following change takes care of the problem.

twoway connected gain_precision n if gain_precision!=., xlabel(4(1)30, labsize(vsmall)) ylabel(0(0.1)0.6)

[Jane Skinner]

Oh, of course! Thanks very much, William.