Okay, a beer brewer might be an understatement for an Oxford University graduate of chemistry and mathematics, William Sealy Gosset, but the fact is that this chemist did start his career as an apprentice brewer at the Dublin’s Guinness brewery.Īt the time, Guinness started employing scientist brewers so as to find a way to produce large quantities of beer, while maintaining the quality standards. How a Guinness Genius Left a Legacy in Statistics: The Origins of the T-Testĭid you know that one of the most used statistical tests, the t-test, was developed by a beer brewer? This is where t-tests kick in.īefore I show you how to conduct a t-test and how to use Microsoft Excel as a t-test calculator, let’s just briefly explore the origin of this type of tests. While it takes no particular wisdom to decide whether two numbers are different, learning whether that difference is statistically significant requires a bit more skill and effort. 2.Analyzing survey results, in most cases, means more than just merely comparing two numbers or graphs. We have 14 degrees of freedom, so we'll look at this row right over here. Remember, our degrees of freedom, our degree of freedom here, Either way, we're in thisĬolumn right over here. Let me do it in a slightly brighter color, which would be that tail Look for a tail probability of 0.01, which is, youĬan't see right over there. Tail, so if you're looking at your t distribution,Įverything up to and including that top 1%, you would Another way of thinking aboutĪ confidence level of 98%, if you have a confidence level of 98%, that means you're leaving 1% unfilled in at either end of the Want a confidence level of 98%, you're going to look at this column, you're going to look at Our confidence levels right over here, so if you What's useful about this t table is they actually give Let's get our t table out, and I actually copied and pasted thisīottom part and moved it up so you could see the whole thing here. We want a 98% confidence interval and we want a degree of freedom of 14. When we're thinking about a confidence interval for your mean. Size and it's going to be your sample size minus one Your degree of freedom is based on the sample More advanced conversations about degrees of freedom,īut for the purposes of this example, you need to know that when you're looking at the t distribution for a given degree of freedom, Sample standard deviations and how to have an unbiased estimate for the population standard deviation. We talked a little bitĪbout degrees of freedom when we first talked about Situation our degree of freedom is going to be equal to 14. Of freedom is going to be 15 minus one, so in this The different sample sizes, depending on the degrees of freedom, and your degree of freedom is going to be your sample size minus one. It's actually a pretty deep concept, but it's this idea that youĪctually have a different t distribution depending on To take into consideration when we're looking up theĪppropriate critical value on a t table, and that's this The key thing to realize is there's one extra variable Guess we call it a t table instead of a z table, but Should use in this situation? We're about to look at, I What they're asking us is what is the appropriate critical value? What is the t star that we Size, which in this case is going to be 15, so Underestimate the margin of error, so it's going to be t star times the sample standard deviation divided by the square root of our sample The t distribution here because we don't want to Now in other videos we have talked about that we want to use So we're going to go take that sample mean and we're going to go plus or But we also want to constructĪ 98% confidence interval about that sample mean. Here we're going to take a sample of 15, so n is equal to 15, and from that sample we can calculate a sample mean. There's a parameter here, let's say it's the population mean. Of what's going on here, you have some population. What is the critical value, t star or t asterisk, for constructing a 98% confidence interval for a mean from a sample size of n isĮqual to 15 observations? So just as a reminder
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