As we go further in our statistical careers, it's going to be valuable to assume that certain distributions are normal distributions or sometimes to assume that they are binomial distributions because if we can do that, we can make all sorts of interesting inferences about them when we make that assumption. But one of the key things about normal distributions or binomial distributions is we assume that they're the sum or they can be viewed as the sum of a bunch of independent trials. So we have to assume that trials are independent. Now that is reasonable in a lot of situations, but sometimes, let's say you're conducting a survey of people exiting a mall, and in that case, and let's say you're saying whether they have done their taxes already, if they're exiting the mall, it's hard to do these samples with replacement. They're leaving the mall. You can't say, hey, hey, wait, I just asked you a question. Now you've answered it.