To determine whether the test is two-tailed, left-tailed, or right-tailed, we need to understand the nature of the claim being tested.

In this case, the claim is that "less than 11% of treated subjects experienced headaches."

This implies that the test is:

• Left-tailed test: because we are testing if the proportion is less than 0.11 (11%).

Given the context of the problem and the claim, we can conclude that the test is left-tailed.

If you have any more questions or need further details, feel free to ask!

Here are some related questions you might be interested in:

1. How do you interpret the z-value in a hypothesis test?
2. What does the p-value indicate in this context?
3. How do you calculate the test statistic for a proportion test?
4. What assumptions must be met to use the normal distribution as an approximation to the binomial distribution?
5. How do you determine the significance level in hypothesis testing?

Tip: In hypothesis testing, clearly understanding the direction of the test (left-tailed, right-tailed, or two-tailed) is crucial, as it influences how you interpret the test statistic and p-value.