Stata tip #34: tab1

Command tabulate or tab is perhaps the first and the most useful commands for any Stata user. Command tab displays a table of frequencies and percentages for a variable, when used with one variable. When used with two variables, it produces a two-way table of frequencies distribution. You could add percentages to the two-way table by including column and row percentages.

Recently I came across a command called tab1, which is an offspring of command tabulate, used to create table of frequencies and percentages for more than one variable, in one command. In other words, if you want to perform tabulate command more than once, and type as many line of code as the number of variables, tab1 can save time by doing so with just one line of code.

You could also think of tab1 as a loop – see Stata tip #33 for loops – which repeats command tabulate for a list of variables.

Let’s see some examples now.

NOTE: I am using The Asia Foundation’s A Survey of the Afghan People (2014) data in my examples. If you do not have this data, you can download it from the following below:

http://afghansurvey.asiafoundation.org/download/

Examples:

Suppose you want to see frequency distribution (table of frequencies) of q6a, q6b, q6c, q6d, q6e and q6f questions. The long way is to type five commands for six mentioned variables:

tab q6a

tab q6b

tab q6c

tab q6d

tab q6e

tab q6f

Another way of doing the above 6 commands is to use loops, command foreach (see Stata tip #33):

foreach x in q6a q6b q6c q6d q6e q6f {

tab `x’

}

A shorter and more straightforward command for doing tab multiple times is to use tab1. For tab1, all you have to do is list all the variables you want after tab1, like below:

tab1 q6a q6b q6c q6d q6e q6f

Although loops are usually the most convenient way of performing a single command over a number of variables, tab1 is the easiest way of obtaining table of frequencies and percentages, i.e. looping tab, for a number of variables.

There are some options available with command tab1, as well as tab. The most commons are missing, nolabel, plot and sort. As a general rule in Stata, options come after a comma.

Option missing requests that missing values, if available, be treated like other values in counts, percentages and other statistics (in composite command tab, sum( ) – see Stata tip #5). The command with missing would look like:

tab1 q6a q6b q6c q6d q6e q6f, missing

Option nolabel causes the numeric codes to be displayed rather than the value labels:

tab1 q6a q6b q6c q6d q6e q6f, nolabel

Option plot adds a simple bar chart of relative frequencies, while omitting the percentage and cumulative columns, to the command tab1:

tab1 q6a q6b q6c q6d q6e q6f, plot

And finally, option sort puts the tables in descending order of frequency/percentage.

Note, if interested, there is no limit to the number of options to be used with one command. Therefore, you can use any number of options at once.