**Introduction**

A binomial probability test is what you use in order to determine whether an observed proportion from a binomial experiment is equal to, less than, or greater than some hypothesized proportion. In this blog, you’ll learn how to carry out a binomial probability test in Stata.

**Motivation and Data Creation**

Let’s say that you polled 111 people in New York City on whether they would support the passage of a particular law, with support = 1 and opposition = 0.

set obs 111

gen a_sup = runiform(0,1)

gen sup = round(a_sup)

drop a_sup

label variable sup "Support"

label define sup 0 "Rejects" 1 "Supports"

label value sup sup

Now let’s say that, nationally, support for this law was at 35%, and you want to test the difference between the level of support in New York City and the level of national support.

Hence,

H0: NYC level of support = .35

HA: NYC level of support ≠ .35.

**Run the Binomial Probability Test**

bitest support == .35

Here’s what you get:

You would therefore reject your null hypothesis, as the proportion of support in NYC, 0.51, is significantly different from the hypothesized proportion of .35, *p *= .000450. In fact, you could express this result in a one-tailed way as well, noting that the proportion of support in NYC is significantly greater than .35, *p *= .000297.

**Graphic Support**

You can show the **proportion mean and 95% confidence interval (CI**) with the following code:

ciplot sup

BridgeText can help you with all of your **statistical analysis needs**.