value.\" This is where we enter the value specified in the null hypothesis which in our case is 12. All you tave to do now is click on OK. rou should see two output boxes. The rst box will have four values in it. N is the number of cases for which we have valid informationij (i.e.. the number of respondents who answered the question). In this problem, N equals 2,537. Mean is the mean years of school completed by the respondents in the sample who answered the question (see STAT2S). In this problem, the sample mean equals 13.68. Standard Deviation is a measure of dispersion {see STAT2S). In this problem. the standard deviation equals 3.07. Standard Error of the Mean is an estimate of how much sampling error there is. In this problem, the standard error equals .06. The second box will have ve values in it. t is the value of the t test df is the number of degrees of freedom Signicance (2-tailed) value Mean Difference 95% Condence Interval of the Difference which we're not going to discuss in this exercise There is a formula for calculating the value oft in the t test. Your instructor may or may not want you to earn how to calculate the value oft. I'm going to leave it to your instructor to do this. In this problem t equals 27.51. Degrees of freedom (of) is the number of values that are free to vary. If the sample mean equals 13.68 hen how many values are free to vary? The answer is N 1 which is 2,53? 1 or 2,536. See if you car igure out why its 2,536. Your instructor will help you if you are having trouble figuring it out. The signicance value is a probability. It's the probability that you would be wrong if you rejected the null typothesis. It's .000 which you would think is telling you that there is no chance of being wrong if you ejected the null hypothesis. But it's actually a rounded value and it means that the probability is less tha 0005 or less than five in ten thousand. So there is a chance of being wrong but it's really, really small. The mean difference' Is the difference between the sample mean {13. 68) and the value specified in the tull hypothesis {12). So it's 13. 68 12 or 1. 68. L; That's the amount that your sample mean differs from :he value' In the null hypothesis. If its positive, then your sample mean is larger than the value in the null and if it's negative, then your sample mean is smaller than the value in the null. \\Iow all we have to do is figure out how to use thet test to decide whether to reject or not reject the null typothesis. Look again at the significance value which is less than .0005. That tells you that the Jrobability of being wrong if you rejected the null hypothesis is less than five out of ten thousand. With JddS like that, of course. we're going to reject the null hypothesis. A common rule is to reject the null typothesis if the significance value is less than .05 or less than five out of one hundred. But wait a minute. The PSPP output said this was a two-tailed signicance value. What does that mean\". Look back at the research hypothesis which was that the population mean was greater than 12. We're