Stat 1000 Tips for Inferences for the Mean using t
Published: Mon, 11/29/10
Hi ,
You are receing this e-mail because you indicated when you signed up for Grant's Updates that you are taking Stat 1000 this term. If in fact, you are not taking Stat 1000, please reply to this e-mail and let me know, and I will fix that.
Note that my final exam prep seminar is coming up this Saturday, Dec. 4. Please go to www.grantstutoring.com for more info and to register. Click the "Seminars" button.
Throughout the term I will send you all sorts of tips to help you study and learn the course. You probably already have done so, but, if not, I strongly recommend you purchase my Basic Stats 1 Study Book. You will find it a great resource to learn the course. I pride myself in explaining things in clear, everyday language. I also provided numerous examples of all the key concepts with step-by-step solutions. You can order my book at UMSU Digital Copy Centre at University Centre at UM campus. They make the book to order so please allow one business day. The book is split into two volumes and each volume costs $45 + tax.
If you ever want to look back over a previous tip I have sent, do note that all my tips can be found in my archive. Click this link to go straight to my archive:
Tips about Inferences for the Mean using t
These tips apply to HW11 for those of you doing the distance/online version of the course. I assume the rest of you will also have similar questions on your next assignment.
Study Lessons 8 and 9 in my book, if you have it, to prepare for this topic.
First, note that, if your assignment, gives you s, the sample standard deviation, instead of σ, the population standard deviation, you must use t. Remember, t has n - 1 degrees of freedom.
If you are asked for the standard error of the sample mean, that is not the standard deviation. I discuss the Standard Error of the sample mean in Lesson 8 of my book.
Note the margin of error of any confidence interval is everything that comes after the +/- in the appropriate formula.
Look at my examples 8, 9 and 10 in Lesson 9 to understand how to put bounds on a P-value if you are using t. BE CAREFUL! In Web Assigne, when you are entering the critical values and tail area bounds into your boxes always put the smaller value in the left box and the larger value in the right box because the < signs demand that.
Watch out for a matched pairs problem. Study my questions 19 and 20 in Lesson 9 to understand how to do hypothesis tests for matched pairs.
To use JMP to do a matched pairs test, copy and paste the data into New Data Table the usual way then select "Analyze", "Matched Pairs". Highlight both columns of your matched pairs data and click "Y, Paired Response" and click OK. You will then be given all the numbers you need.
If you want to use Crunchit! (and I wouldn't) copy the "http:..." stuff for the link to the data (shown at the top in your web browser) then select "Data" and "Load Data from URL". Paste the link into the box and make sure the box saying "use first line as column names" is selected. Make sure you have selected "whitespace" as the delimiter to separate your columns. Now click "Statistics", "T tests", and "Paired". Highlight column 1 in the first box and column 2 in the second box. Be sure to select the correct alternative hypothesis and set the appropriate confidence level, then click OK to get your printout.
To test hypotheses using JMP or make confidence intervals using JMP, see my previous tips I have sent. Note, if you are not given σ, obviously do not enter a value for σ in the pop-up boxes.
If you want to use Crunchit! to do a hypothesis test using t, copy the "http:..." stuff for the link to the data (shown at the top in your web browser) then select "Data" and "Load Data from URL". Paste the link into the box and make sure the box saying "use first line as column names" is selected. Now, you should see the data in your spreadsheet. Select "Graphics" and then select "Histogram". Highlight the appropriate column of data and click "OK" to get a histogram. Copy and paste it into your document. Select "Statistics", then select "T tests", then select "One-sample". In the pop-up window, make sure you click the appropriate variable in the "Variable" box to highlight it. Type in the mean you are using in your null hypothesis. Be sure you click whether you are doing a two-sided, upper-tailed (greater than) or lower-tailed test (less than) or else you will not be given the correct P-value. Click "OK". You now get a printout showing, among other things, the test statistic and P-value.
In either case (JMP or Crunchit!), you can now select, copy and paste your output to a file ready for upload as usual.
Make sure you read my section on P-values to learn how to properly interpret your P-value. All that is required is one or two sentences. Do not think you have to write an essay, and don't think you have to really write something that a "layman" will understand. A layman is never going to understand a P-value, even if you spent three pages trying to explain it.