Statistics How To

Hypothesis Testing > Welch’s Test for Unequal Variances What is Welch’s Test for Unequal Variances? Welch’s Test for Unequal Variances (also called Welch’s t-test, Welch’s adjusted T or unequal variances t-test) is a modification of Student’s t-test to see if two sample means are significantly different. The modification is to the degrees of freedom used … Read more

Types of Variables > Grouping Variable What is a Grouping Variable? A grouping variable (also called a coding variable, group variable or by variable) sorts data within data files into categories or groups. It tells a computer system how you’ve sorted data into groups. Grouping variables can be: Categorical variables: a category like “Male” or … Read more

Multivariate Analysis > Wilks’ Lambda What is Wilks’ Lambda? Wilks’ lambda (Λ) is a test statistic that’s reported in results from MANOVA , discriminant analysis, and other multivariate procedures. Other similar test statistics include Pillai’s trace criterion and Roy’s ger criterion. In MANOVA, Λ tests if there are differences between group means for a particular … Read more

Probability and Statistics Topic Index > SPSS for Statistics > How to Enter Data into SPSS and Define Variables SPSS looks a little like Microsoft Excel. At first glance, you might think you can type your data into the spreadsheet in the same way as you can in Excel. However, this isn’t the case. With … Read more

Statistics Definitions > Quantile What is a Quantile? The word “quantile” comes from the word quantity. In simple terms, a quantile is where a sample is divided into equal-sized, adjacent, subgroups (that’s why it’s sometimes called a “fractile“). It can also refer to dividing a probability distribution into areas of equal probability. The median is … Read more

Statistics Definitions > Stratum What is a Stratum? Stratum in geology or biology refers to layers, as in a layer of rock or layer of skin. A stratum in statistics isn’t much different — you can think of it as where your target population is divided into non-overlapping layers, subgroups, or categories. For example, strata … Read more

Probability and Statistics Index > Excel for Statistics > Excel Multiple Regression Excel multiple regression can be performed by adding a trendline, or by using the Excel Data Analysis Toolpak. If you just want to know the equation for the line of best fit, adding a trendline will work just fine. If you want to … Read more

Statistics Definitions > Pascal’s Triangle Pascal’s Triangle is a number pattern in the shape of a (not surprisingly!) a triangle. It is named after the French mathematician Blaise Pascal. Pascal’s Triangle has many applications in mathematics and statistics, including it’s ability to help you calculate combinations. Row 0 1 Row 1 1 1 Row 2 … Read more

Types of Variables > Control Variable An experiment has several types of variables, including a control variable (sometimes called a controlled variable). Variables are just values that can change; a good experiment only has two changing variables: the independent variable and dependent variable. Let’s say you are testing to see how the amount of light … Read more

Statistics Definitions > Type III error and Type IV Error What is a Type III error? A type III error is where you correctly reject the null hypothesis, but it’s rejected for the wrong reason. This compares to a Type I error (incorrectly rejecting the null hypothesis) and a Type II error (not rejecting the … Read more