Computing the test statistic and p-value in minitab express

#COMPUTING THE TEST STATISTIC AND P VALUE IN MINITAB EXPRESS HOW TO#
#COMPUTING THE TEST STATISTIC AND P VALUE IN MINITAB EXPRESS FREE#

Use this test if you know that the two populations' variances are the same (or very similar). For your convenience, we describe both versions. There is a version of a t-test which can be applied without the assumption of homogeneity of variance: it is called a Welch's t-test. Ојв‚Ѓ and Ојв‚‚ are different from one another ДЇormally, to perform a t-test, we should additionally assume that the variances of the two populations are equal (this assumption is called the homogeneity of variance).The alternate hypothesis is that the population means are: The null hypothesis is that the population means are equal. In particular, if this pre-determined difference is zero ( О” = 0): The alternative hypothesis is that the difference Ојв‚Ѓ - Ојв‚‚ is: The null hypothesis is that the actual difference between these groups' means, Ојв‚Ѓ and Ојв‚‚, is equal to some pre-set value, О”. Gosset worked at the famous Guinness Brewery in Dublin, Ireland, and devised the t-test as an economical way to monitor the quality of beer. The t-Student distribution owes its name to William Sealy Gosset, who, in 1908, published his paper on the t-test under the pseudonym 'Student'. If the number of degrees of freedom is large (>30), which generically happens for large samples, the t-Student distribution is practically indistinguishable from N(0,1).Дensity of the t-distribution with ОЅ degrees of freedom

This distribution has a shape similar to N(0,1) (bell-shaped and symmetric) but has heavier tails. If there are d degrees of freedom, then the distribution of the test statistics is the t-Student distribution with d degrees of freedom. The degrees of freedom are essential, as they determine the distribution followed by your t-score (under the null hypothesis). Again, the exact formula depends on the t-test you want to perform - check the sections below for details.

In the simplest case, the number of degrees of freedom equals your sample size minus the number of parameters you need to estimate.

#COMPUTING THE TEST STATISTIC AND P VALUE IN MINITAB EXPRESS FREE#

The degrees of freedom are the number of observations in a sample that are free to vary as we estimate statistical parameters. The exact formula depends on the t-test type - check the sections dedicated to each particular test for more details.Дetermine the degrees of freedom for the t-test: Use a one-tailed t-test if you want to test whether this mean (or difference in means) is greater/less than the pre-set value.ДЇormulas for the test statistic in t-tests include the sample size, as well as its mean and standard deviation. Use a two-tailed t-test if you only care whether the population's mean (or, in the case of two populations, the difference between the populations' means) agrees or disagrees with the pre-set value.

#COMPUTING THE TEST STATISTIC AND P VALUE IN MINITAB EXPRESS HOW TO#

These next steps will tell you how to calculate the p-value from t-test or its critical values, and then which decision to make about the null hypothesis. So, you've decided which t-test to perform.

The change in blood pressure in patients before and after administering some drug.

The change in student test performance before and after taking a course.In particular, you can use this test to check whether, on average, the treatment has had any effect on the population. This test is sometimes referred to as an independent samples t-test, or an unpaired samples t-test.ДЄ paired t-test is used to investigate the change in the mean of a population before and after some experimental intervention, based on a paired sample, i.e., when each subject has been measured twice: before and after treatment. The average difference in the results of a math test from students at two different universities.The average difference in weight gain in two groups of people: one group was on a high-carb diet and the other on a high-fat diet.In particular, you can use this test to check whether the two groups are different from one another. The average weight of people from a specific city - is it different from the national average?Д¬hoose the two-sample t-test to check if the difference between the means of two populations is equal to some pre-determined value, when the two samples have been chosen independently of each other.The average volume of a drink sold in 0.33 l cans - is it really equal to 330 ml?.Your choice of t-test depends on whether you are studying one group or two groups:Д¬hoose the one-sample t-test to check if the mean of a population is equal to some pre-set hypothesized value.

Computing the test statistic and p-value in minitab express