In ANOVA, we always report the F-value, degrees of freedom (df) and p for each effect -possibly just one for one-way ANOVA. P (“Sig.” in SPSS) tells us the likelihood of some effect being zero in our population. However, it doesn’t tell us how strong some effect is if it is not zero; we can’t conclude that p = 0.05 indicates a […]
The Kruskal-Wallis test is an alternative for a one-way ANOVA if the assumptions of the latter are violated. We’ll show in a minute why that’s the case with creatine.sav, the data we’ll use in this tutorial. But let’s first take a quick look at what’s in the data anyway. Quick Data Description Our data contain the result of a small […]
Null Hypothesis Assumptions Levene’s test in SPSS Output Reporting Levene’s Test – What Is It? If we want to compare 3(+) groups on a metric variable, we usually want to know if they have different mean scores. In most cases, we’ll run an ANOVA in order to find out. However, this requires the homogeneity assumption which states that the population […]
The median test for independent medians tests if two or more populations have equal medians on some variable. That is, we’re comparing 2(+) groups of cases on 1 variable at a time. Rating Car Commercials We’ll demonstrate the median test on adratings.sav. This file holds data on 18 respondents who rated 3 different car commercials on […]
The Mann-Whitney test is an alternative for the independent samples t test when the assumptions required by the latter aren’t met by the data. The most common scenario is testing a non normally distributed outcome variable in a small sample (say, n < 25).* The Mann-Whitney test is also known as the Wilcoxon test for independent samples -which shouldn’t be confused […]
Null Hypothesis Assumptions Chi-Square Independence Test in SPSS Output Reporting Null Hypothesis Chi-Square Independence Test A chi-square independence test evaluates if two categorical variables are associated in some population. We’ll therefore try to refute the null hypothesis that two categorical variables are (perfectly) independent in some population.If this is true and we draw a sample from this population, then we […]
If you’d like to know if 2 groups of people score similarly on 1 dichotomous variable, you’ll compare 2 independent proportions. There’s two basic ways to do so: the chi-square independence test and; the z-test for 2 independent proportions. These tests yield identical significance levels but the z-test approach allows you to compute a confidence interval for the difference between […]
SPSS one-sample t-test tests if the mean of a single metric variable is equal to some hypothesized population value. The figure illustrates the basic idea. SPSS One Sample T-Test – Example A scientist from Greenpeace believes that herrings in the North Sea don’t grow as large as they used to. It’s well known that – on average – […]
A sign test for one median is often used instead of a one sample t-test when the latter’s assumptions aren’t met by the data. The most common scenario is analyzing a variable which doesn’t seem normally distributed with few (say n < 30) observations. * This tutorial shows how to run and interpret a sign test in SPSS. We’ll […]
SPSS one-sample chi-square test is used to test whether a single categorical variable follows a hypothesized population distribution. SPSS One-Sample Chi-Square Test Example A marketeer believes that 4 smartphone brands are equally attractive. He asks 43 people which brand they prefer, resulting in brands.sav. If the brands are really equally attractive, each brand should be chosen by roughly […]
The binomial test is the most simple statistical test there is. Understanding how it works shouldn’t be too hard and will help you understand other statistical tests more easily too. So what is it? A binomial test is a procedure for evaluating if some population proportion is x. For example, a marketeer has to make sure that 50% […]
There’s two basic tests for testing a single proportion: the binomial test and the z-test for a single proportion. For larger samples, these tests result in roughly similar significance levels. However, the binomial test only comes up with a 1-tailed p-value unless the hypothesized proportion = 0.5. Moreover, it can’t compute a confidence interval for your proportion. The […]
The vast majority of statistical tests really just compare several populations on one variable or compare several variables in one population. Now, if we add to this comparison the number of variables or populations and the measurement levels of our variables then choosing the appropriate statistical test suddenly becomes remarkably easy.* The overviews below also nicely visualize how basic tests relate […]
Aggregate is an SPSS command for creating variables holding statistics over cases. This tutorials briefly demonstrates the most common scenarios and points out some best practices. SPSS Aggregate Command The SPSS AGGREGATE command typically works like so: One or more BREAK variables can be specified.* All cases with the same value(s) on the break variable(s) are referred to as a break group Each […]
Summary SPSS MEANS produces tables containing means and/or other statistics for different groups of cases. These groups are defined by one or more categorical variables. If assumptions are met, MEANS can be followed up by an ANOVA. This tutorial walks through its main options, pointing out some tips and tricks. You may follow along by downloading and opening freelancers.sav. […]
Summary SPSS DESCRIPTIVES generates a single table with descriptive statistics for one or more variables. It can also add z-scores to your data. We’ll walk through its major options using freelancers.sav. The screenshot below shows part of its data view. User Missing Values Before running any descriptives, we first need to specify some user missing values for income_2010 through […]
Introduction Using SPSS keywords, especially TO and ALL greatly speeds up a myriad of typical tasks. This tutorial walks you through SPSS main keywords and points out how they can save time and effort. We’ll use supermarket.sav for demonstrational purposes. SPSS Main Keywords EXPRESSION MEANING RETURNS ALL All variables (not previously addressed in statement) Variable name(s) TO All variables between and […]
This tutorial shows how to compute means over both variables and cases in a simple but solid way. We encourage you follow along by downloading and opening restaurant.sav, part of which is shown below. Quick Data Check Before computing anything whatsoever, we always need to know what’s in our data in the first place. Skipping this […]
For converting string variables to date variables, ALTER TYPE is the way to go. This tutorial demonstrates how to do this and points out a couple of caveats. For those who can’t use ALTER TYPE, we’ll propose some alternatives. SPSS Alter Type The syntax below first creates a mini dataset holding 8 string variables. They demonstrate the 8 most common date formats. Next, […]
A course was evaluated by 183 students. The data are in course_evaluation.sav, part of which is shown below. The teacher wants to know the average age of his students but we only have their date of birth. 1. Ensure Date of Birth is a Date Variable The first thing we’ll do is check if date of […]
