T test example problems pdf

This is a useful tip in understanding the necessary critical value of a t test for it to reach statistical significance. The technical details and formulas for the methods of this procedure are presented in line with the example 1 output. T is also computed from the data, so it is a statistic. If acrobat or reader can open the sample form, then the other pdf could be damaged or the web server could be having problems. These reports include confidence intervals of the mean or median, the t test, the z test, and nonparametric tests. Our t test will have df equal to the total of our sample sizes minus 2. Introduction the t test is a basic test that is limited to two groups. A paired ttest is used to compare two population means where you have two samples in which observations in one sample can be paired with observations in. Compute the appropriate ttest for the data provided below. Select the variable weight to be analyzed into the test variable box, and enter the test value which the average value to be tested with the mean value specified in the null hypothesis, that is 140 in this example. The repeatedmeasures t test also known as the pairedsamples or related t test is used when participants provide data for each level or condition of the independent variable in a withinparticipants design for example, before and after an intervention. Following a ten day recovery period, rats kept at 80 percent body weight are tested for the number of chocolate chips consumed during a 10 minute period of time both with and without electrical stimulation.

For example, see if this sample form displays in your browser. Hypothesis testing with t tests university of michigan. Hypothesis testing with z tests university of michigan. Chapter 205 onesample t test introduction this procedure provides several reports for making inference about a population mean based on a single sample. For this tutorial we will focus on the independent t test. Example ztest form for the problem on page 215 of the textbook. A manufacturer of running shoes knows that the average lifetime for a particular model of shoes is 15 months. Consider the following accident statistics data that record the counts of the number of accidents in each of 647 households during a one year period. Examples of research questions that would use an independent t test. Discussion i essentially we compared the sample means of two samples. An investigator predicts that individuals that fit the type a behavior pattern highly competitive and time conscious will have higher scores on a questionnaire measure of need for achievement that individuals that fit the type b behavior pattern absence of type qualities. An independent testing agency was hired prior to the november 2010 election to study whether or not the work output is different for construction workers employed by the state and. If this is a t test, use alpha, the number of tails and the degrees of freedom to look up the.

Researchers are testing a new blood pressurereducing drug. The independent ttest ttest independent ttest between. The pairedsamples t test also called dependentsamples t test is used to compare two means for situations in which every participant is in both samples or situation of two set of units that are matched in pairs, for example, husbands and. This work is licensed under a creative commons attribution. Due to the increased variability in using the sample standard deviation instead of the population standard deviation, the tdistribution is used in place of the zdistribution. The salary of 6 employees in the 25th percentile in the. When one drug is being tested to replace another, its important to check that the new drug has the same effects on the body as the old drug. In the show the pickup artist, mystery the host wants the artists in training to change from being plain old afcs average frustrated chumps, into master pickup artists. Twosample ttest using r 33 twosample ttest using r t. As part of the suit, these advocates have collected data on all houses purchased by. Unit 7 hypothesis testing practice problems solutions. The repeatedmeasures ttest also known as the pairedsamples or related ttest is used when participants provide data for each level or condition of the independent variable in a withinparticipants design for example, before and after an intervention.

He insists that one way to help increase your confidence and. For this tutorial we will focus on the independent ttest. Expenza, a namebrand drug is being used to lower blood pressure. The first three steps are identical to those in note 9. The output and technical details are presented in the following order. Skewness, kurtosis, more than one mode, and a host of other problems will be. Populations, distributions, and assumptions populations. Summary in this howto guide we have described the basics of a t test. Lecture 12 hypothesis testing allatorvostudomanyi egyetem. The focus will be on conditions for using each test, the hypothesis tested by each test, and the appropriate and inappropriate ways of using each test. All students at umd who have taken the test not just our sample 2.

Look up the significance level of the zvalue in the standard normal table table 2 in statistics tables when the standard deviation of the sample is substituted for the standard deviation of the population, the statistic does not. The null hypothesis is that there is no significant difference in average test scores between females and males in the population. If this is a ttest, use alpha, the number of tails and the degrees of freedom to look up the critical value in a ttable. Use the questions, datasets, and answers provided below to finetune your skills.

The t test and basic inference principles the t test is used as an example of the basic principles of statistical inference. Collect sample of males and sample of females and ask their opinions on whether capital punishment should be legal. I in the next lecture we will see more about comparing the means and distributions of two samples. Solution for the acceptance region of a one sided test with alpha. A premium golf ball production line must produce all of its balls to 1. Troubleshoot viewing pdf files on the web adobe inc. One sample hypothesis test of means or t tests note that the terms hypothesis test of means and ttest are the interchangeable. The second section, onesample test, displays the results most relevant to the one sample t test. Blood pressure and oral contraceptive use bp before oc bp after oc afterbefore 1.

Here are the sat scores from the 25 students who completed the sat prep program. But for t to be an useful statistic, we need to know its distribution. Collect sample of iron pans and sample of copper pans and measure their resiliency at high temperatures. Observed actual count values in each category expected the predicted expected counts in each category if the null hypothesis were true conducting a chisquare test is much like conducting a. I our goal was to understand if the true mean of the rst sample was greater than the true mean of the second. The independent t test depends on the means, standard deviations and sample sizes of each. T test for independent samples solution victor bissonnette. Twosample t test this example will use the same data as the previous example to test whether the difference between females and males average test scores is statistically significant. The ttest and basic inference principles the ttest is used as an example of the basic principles of statistical inference. They are just two different names for the same type of statistical test. The test statistic of the onesample t test, denoted t. One sample t test as in the following picture, and the onesample t test dialog box will appear on the screen. A researcher is interested in the affects that a persons avatar i. To evaluate the statistical significance of the t test, you need to compute the p.

Twenty five high school students complete a preparation program for taking the sat test. Example ttest of pearsons r form for the problem on page 324 of the textbook null hypothesis. Summary in this howto guide we have described the basics of a ttest. I made these practice questions and answers in somewhat of a rush, and there may be some mistakes. To evaluate the statistical significance of the ttest, you need to compute the p. Rejection occurs for tscore the 99th percentile of a students t on df9 rejection occurs for tscore t. These reports include confidence intervals of the mean or median, the ttest, the. For multiple groups, you would have to compare each pair of groups, for example with three groups there would be three tests ab, ac, bc, whilst with seven groups there would need to be 21 tests. A random sample of 22 fifth grade pupils have a grade point average of 5. The observed significance or pvalue of the test is the area of the right tail of the standard normal distribution that is cut off by the test statistic z 5. The number we entered as the test value in the onesample t test window. The ttest, or students test, compares the mean of a vector against a theoretical mean.

Observed actual count values in each category expected the predicted expected counts in each category if the null hypothesis were true conducting a chisquare test is much like conducting a z test or t test. Example ztest form for the problem on page 215 of the. Technology stepbystep twosample ttests dependent sampling. Someone in the research and development division of the shoe company claims to have developed a longer lasting product. This new product was worn by 30 individuals and lasted on average for 17 months. One of the simplest situations for which we might design an experiment is the case of a nominal twolevel explanatory variable and a quantitative outcome variable. If the production line gets out of sync with a statistical significance of more than 1%, it must be shut down and repaired. The t test, or students test, compares the mean of a vector against a theoretical mean.