05 One-Sample t-Tests in SPSS – SPSS for Beginners

Welcome to the fifth video in SPSS for Beginners from RStats Institute at Missouri State University. Earlier, we learned how to calculate means using SPSS, so now I'm going to show you how we test whether two means are different (or not) using a procedure called the one sample t-test. T tests are easy to do in SPSS. In the next three videos, we will learn about three kinds of T tests. Each of them will use the data set that we created in the first video. I'm interested in the variable Height. Specifically, I want to know if my participants are taller or shorter than the national average. Perhaps we sampled these people from a certain country and we want to know how they compare to the average American. Or perhaps they have a certain disorder and I want to know how they compare to the typical average healthy person. Or perhaps these are children who grew up eating a certain diet and I want to know if that diet affected their height compared to an average child. So what I have is one group of people whom I have measured one time. I want SPSS to calculate the mean from my sample and then compare that sample mean to another known mean. And to do this, I'm going to use a one sample t-test. Go to Analyze -> Compare Means -> One Sample t-Test. A window pops up just like we have seen before. We will move our variable Height into the Test Variables box. We can do that with the arrow or just by dragging it over. And then we need to set our hypothesized population mean in this box - labeled Test Value. So imagine that we went to the scientific literature and we read that other people, similar to this sample, have an average height of 65 inches tall. I want SPSS to calculate this sample mean and then compare it to the known value of 65. So, click OK. The output window will pop up and you will see two tables. The first table contains our descriptive statistics, just like we've calculated before. We see the mean, standard deviation, and something called the standard error of the mean. The second table contains our inferential statistics, and this is where we find out if the mean of our sample is significantly different from 65, or not. We have the t-score right here, the degrees of freedom (which is n - 1) the number of scores minus 1, and finally the p-value that corresponds to this t-score at this degrees of freedom. In the box "Sig. (2-tailed)." There are three ways that we can determine if one mean is statistically significantly different from another mean. The first is by looking at the t-value. We would go to a table called "Students t-Table" and look up a Critical Value. If the T value is larger than the critical value from that table, then the means are different. A second way is to look at the p-value. Typically, scientists and researchers use p < .05 as the cutoff for statistical significance, where any values .05 or less are said to be "statistically significant." A third way of determining significance is to look at the confidence interval. We are testing a hypothesis that the mean difference was 0. So if the 95% confidence interval includes 0, then the means are NOT different. So, I looked up the critical value on Students t-Table and I found that for a test with 9 degrees of freedom, the critical value is 2.262. This t value is smaller than 2.262. I can see that the p-value is .318, which is larger than .05. And finally, I can see that the lower confidence interval is negative but the upper value is positive, so this confidence interval crosses zero. These three findings all tell us the same thing: the mean of our sample 65.8 is NOT different than the national average of 65. Our sample was pretty much the same height as our comparison group. And that is how you do a one sample t-test in SPSS. When you are ready to do a real one sample t-test, check out these other videos from RStats Institute that will teach you more about statistical theory, setting up the test, interpreting the results, and writing up your findings in APA style.

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Keywords: SPSS for beginners, Todd Daniel, statistics, flipped classroom, SPSS, beginners, introduction, diving, deeper, how to, how to do, how to use SPSS, introduction to SPSS, t test, one sample t test, single sample t test, online, teaching, learning, instruction

Id: C2Qa5d9ij0Y

Length: 6min 2sec (362 seconds)

Published: Thu Dec 07 2017