 Hello, we are now going to look at two sample hypothesis testing, actually building a confidence interval for two proportions. In this example, which was in a previous video where we did the full hypothesis test, we want to test to claim the alternative hypothesis at a significance level of 0.01. We obtained 67% successes in sample size of 800 for the first population and 73% successes in a sample size of 300 for the second population. So what is the confidence interval for the difference, the proportion of the first population minus the proportion of the second population? So one thing to watch out for here is this is a one-tailed test, in this case it's left-tailed. So whenever we draw the picture of this with our bell curve, we have a left-tail. And we know that the area of that left-tail is alpha or 0.01. Here's the deal. Anytime we can make a confidence interval, confidence intervals back when we learned them, we had tails on both sides of the bell curve. So you actually need to make sure you have two tails when you make a confidence interval. This tail on the right actually has area of alpha as well, 0.01. Left-tail, right-tail always have the same area. So alpha in this case is 0.01. So what does that leave for the area in the middle here where we're building the confidence interval? Well it's actually 0.98. It's 1 minus alpha twice. So here's the general rule. First, for a two-tailed test, your confidence level is always equal to 1 minus alpha. For a one-tailed test, though, which is what's happening here, your confidence level is 1 minus 2 times alpha. So in this case, my confidence level is going to be 1 minus 2 times 0.01, which is 0.98. So make sure you take note of this one-tailed test. You have to subtract alpha twice from 1. All right, so let's go ahead and do our information we had to put in the Google Sheets group one. Number of successes in group one is 67 percent. So you do 800 times 0.67. So that gives me 536. And sample size for group one is 800. Group two, you get number of successes is 300 times 73 percent, which is going to give you 219. Sample size for group two is going to be 300. This is what you put into Google Sheets to calculate your confidence interval. In Google Sheets, you will go to the data list tab to proportion confidence level p-value region. For group one, type in successes and the sample size. Group two, type in successes and the sample size. And then you just need to type in your confidence level of 0.98. And you can see that your lower limit is negative 0.13 and your upper limit is 0.01. So let's write out this confidence interval. So the difference of the two proportions, the lower limit is negative 0.13 and the upper limit is 0.01. So what does this mean? Well, it means that with confidence level 98 percent, the difference between the population proportions of the two groups is between negative 0.13 and 0.01. So that's all I have for you. Thank you for watching.