Setting bin size for histogram

[Ian Kingsbury]

I want to create a twoway histogram like the one here: https://stats.idre.ucla.edu/wp-conte.../02/histo3.png

I am comparing certified and non-certified teachers on a construct I have called "relationships." My code looks like this:

twoway (histogram relationship if altcert==1, frequency start(2) bin(3) color(green)) ///
(histogram relationship if altcert==0, frequency start(2) bin(3) ///
fcolor(none) lcolor(black)), legend(order(1 "alt cert" 2 "traditional" ))

The result is that I get a histogram that looks like this: https://imgur.com/a/lhTgn

I want 3 bins that are the same width for both groups. The first one being 2.00-2.74, the second 2.75-2.99, the third being 3-4.

[Nick Cox]

If you want unequal bin widths, you have to leave histogram behind. You need to calculate density yourself and then draw a graph with twoway bar. See also

SJ-15-1 gr0063 . . . . . Stata tip 122: Variable bar widths in two-way graphs
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Jann
Q1/15 SJ 15(1):316--318 (no commands)
highlights the bartype(spanning) option of the twoway bar
command, an undocumented feature that can be used to produce
bars of different widths

and its references.

Otherwise, I presume you're obliged to do this for reasons beyond your control!