Say that you were looking at writing scores broken down by race and ses. You might want to graph the mean and confidence interval for each group using a bar chart with error bars as illustrated below. This FAQ shows how you can make a graph like this, building it up step by step.

First, lets get the data file we will be using.

use http://www.ats.ucla.edu/stat/stata/notes/hsb2, clear

Now, let’s use the **collapse** command to make the mean and standard deviation by
**race** and **ses**.

collapse (mean) meanwrite= write (sd) sdwrite=write (count) n=write, by(race ses)

Now, let’s make the upper and lower values of the confidence interval.

generate hiwrite = meanwrite + invttail(n-1,0.025)*(sdwrite / sqrt(n)) generate lowrite = meanwrite - invttail(n-1,0.025)*(sdwrite / sqrt(n))

Now we are ready to make a bar graph of the data The **graph bar** command makes a pretty
good bar graph.

graph bar meanwrite, over(race) over(ses)

We can make the graph look a bit prettier by adding the **asyvars** option as shown below.

graph bar meanwrite, over(race) over(ses) asyvars

But, this graph does not have the error bars in it. Unfortunately, as nice as the
**graph bar** command
is, it does not permit error bars. However, we can make a **twoway** graph that has error bars as shown
below. Unfortunately, this graph is not as attractive as the graph from **graph
bar**.

graph twoway (bar meanwrite race) (rcap hiwrite lowrite race), by(ses)

So, we have a conundrum. The **graph bar** command will make a lovely bar
graph, but will not support error bars. The **twoway bar** command makes
lovely error bars, but it does not resemble the nice graph that we liked from
the **graph bar** command.
However, we can finesse the **twoway bar** command to make a graph that
resembles the **graph bar** command and then combine that with error bars.
Here is a step by step process.

First, we will make a variable **sesrace** that will be a single variable that contains
the ses and race information. Note how **sesrace** has a gap between the
levels of **ses** (at 5 and 10).

generate sesrace = race if ses == 1 replace sesrace = race+5 if ses == 2 replace sesrace = race+10 if ses == 3 sort sesrace list sesrace ses race, sepby(ses)+---------------------------------+ | sesrace ses race | |---------------------------------| 1. | 1 low hispanic | 2. | 2 low asian | 3. | 3 low african-amer | 4. | 4 low white | |---------------------------------| 5. | 6 middle hispanic | 6. | 7 middle asian | 7. | 8 middle african-amer | 8. | 9 middle white | |---------------------------------| 9. | 11 high hispanic | 10. | 12 high asian | 11. | 13 high african-amer | 12. | 14 high white | +---------------------------------+

Now, we will make a graph using **graph twoway**. Notice how the bars are in
three groups of four bars. The three groups correspond to the three levels of **ses** and
the four bars within each group correspond to the four levels of
**race**. You can relate this grouping to the way that we constructed **raceses** above.

twoway (bar meanwrite sesrace)

We can now overlay the error bars by overlaying a **rcap** graph

twoway (bar meanwrite sesrace) (rcap hiwrite lowrite sesrace)

This kind of looks like what we want, but it would look nicer if each of the
bars for the four different races were different colors. We can do this by
overlaying four separate **bar** graphs, one for each racial group.

twoway (bar meanwrite sesrace if race==1) /// (bar meanwrite sesrace if race==2) /// (bar meanwrite sesrace if race==3) /// (bar meanwrite sesrace if race==4) /// (rcap hiwrite lowrite sesrace)This is looking better, but let’s use the legend to label the bars better.

twoway (bar meanwrite sesrace if race==1) /// (bar meanwrite sesrace if race==2) /// (bar meanwrite sesrace if race==3) /// (bar meanwrite sesrace if race==4) /// (rcap hiwrite lowrite sesrace), /// legend( order(1 "Hispanic" 2 "Asian" 3 "Black" 4 "White") )

The legend labels the bars nicely, but would look cleaner if it were just one row and
the **x** axis of the graph does not convey
that the three groups of bars correspond to the three groups of **ses**. We can
use the **xlabel()** option to remedy that. We also add better titles for the
**x** and **y** axes as well.

twoway (bar meanwrite sesrace if race==1) /// (bar meanwrite sesrace if race==2) /// (bar meanwrite sesrace if race==3) /// (bar meanwrite sesrace if race==4) /// (rcap hiwrite lowrite sesrace), /// legend(row(1) order(1 "Hispanic" 2 "Asian" 3 "Black" 4 "White") ) /// xlabel( 2.5 "Low" 7.5 "Middle" 12.5 "High", noticks) /// xtitle("Socio Economic Status") ytitle("Mean Writing Score")

Now we have a graph that looks like the kind of graph that we would get
from **graph bar** but by finessing **graph twoway bar** into making
this pretty graph, we could then overlay the **rbar** graph to get the
error bars we desired.