Sampling Distribution

A sampling distribution is the frequency distribution of a statistic over many random samples from a single population.Sampling distributions are at the very core of inferential statistics but poorly explained by most standard textbooks. The reasoning may take a minute to sink in but when it does, you’ll truly understand common statistical procedures such as ANOVA or a chi-square test. […]

Z-Scores – What and Why?

Z-scores are linearly transformed data values having a mean of zero and a standard deviation of 1.Z-scores are also known as standardized scores; they are scores (or data values) that have been given a common standard. This standard is a mean of zero and a standard deviation of 1. Contrary to what many people believe, z-scores are not necessarily […]

SPSS Independent Samples T Test

Null Hypothesis Assumptions Independent Samples T Test in SPSS Output Reporting Null Hypothesis The null hypothesis for an independent samples t test is that two populations have equal means on some metric variable. For example, do men spend the same amount of money on clothing as women? We can’t reasonably ask the entire population of men and women how much they […]

Null Hypothesis – Simple Introduction

A null hypothesis is a precise statement about a population that we try to reject with sample data. We don’t usually believe our null hypothesis (or H0) to be true. However, we need some exact statement as a starting point for statistical significance testing. Null Hypothesis Examples Often -but not always- the null hypothesis states there is […]

Statistical Significance

What Does It Really Mean? Statistical significance is the probability of finding a given deviation from the null hypothesis -or a more extreme one- in a sample. Statistical significance is often referred to as the p-value (short for “probability value”) or simply p in research papers. A small p-value basically means that your data are unlikely under some null hypothesis. […]

Standard Deviation

The standard deviation is a number that indicates the extent to which a set of numbers lie apart. Standard Deviation – Example Five applicants took an IQ test as part of a job application. Their scores on three IQ components are shown below. Now, let’s take a close look at the scores on the 3 […]

Variance – What Is It?

The variance is a number that indicates how far a set of numbers lie apart.The variance is identical to the squared standard deviation and hence expresses “the same thing” (but more strongly). Variance – Example A study has 100 people perform a simple speed task during 80 trials. For each participant, 80 reaction times (in seconds) are […]

Simple Random Sampling – What Is It?

Introduction Popular statistical procedures such as ANOVA, a chi-square test or a t-test quietly rely on the assumption that your data are a simple random sample from your population. Violation of this assumption may result in biased or even nonsensical test results and few researchers seem to be aware of this. Plenty of reasons for a brief discussion of simple […]

Histogram – What Is It?

A histogram is a chart that shows frequencies for equal width intervals of values of a metric variable. Histogram – Example A company wants to know how monthly salaries are distributed over 1,110 employees having operational, middle or higher management level jobs. The screenshot below shows what their raw data look like. Since these salaries […]

SPSS FREQUENCIES Command

SPSS FREQUENCIES command can be used for much more than frequency tables; it’s also the easiest way to obtain basic charts such as histograms and bar charts. On top of that, it provides us with percentiles and some other statistics. Plenty of reasons for taking a closer look at this ubiquitous SPSS command. We’ll use employees.sav throughout […]

SPSS Syntax – Six Reasons you Should Use it

Most of us start working with SPSS from its point-click menu. Doing so without pasting and saving all syntax may seem obvious at first but often turns out to be a pitfall. Using SPSS syntax may seem a bit difficult at first but often turns out to save tons of time and effort in the end. This tutorial explains […]

Compute A = B = C

Summary A great way to dichotomize variables is with a single short compute command. This is also the fastest way to create multi variable filters. How Does it Work? When the structure COMPUTE A = B = C is used, SPSS will evaluate whether (B = C) is True or False for each case. The outcome variable A will be the following If (B […]

SPSS SPLIT FILE – A Quick Tutorial

SPLIT FILE is a command for having separate output for subsets of cases. It does not literally split your file into smaller files. Subsets are defined by the values on one or more split variables. After running SPLIT FILE, output is reported for each split group separately until you run SPLIT FILE OFF.Example of output […]

SPSS FILTER – Quick & Simple Tutorial

SPSS FILTER temporarily excludes a selection of cases from all data analyses.For excluding cases from data editing, use DO IF or IF instead. SPSS Filtering Basics Example 1 – Exclude Cases with Many Missing Values Example 2 – Filter on 2 Variables Example 3 – Filter without Filter Variable Tip – Commands with Built-In Filters Warning – Data Editing with […]

SPSS WEIGHT Command

By default, every case in your data counts as a single case. However, you can have each case count as more or less than one case as well. This is called weighting. For instance, the first case in your data may count as 2 cases and the second one as .5 cases. These numbers, the case weights, […]

SPSS Keyboard Shortcuts

SPSS keyboard shortcuts allow you to work with amazing speed. Some of the best SPSS shortkeys are not obvious at all so we’ll list our 20 favorite SPSS shortkeys in the table below.* Enjoy! Overview Most Useful SPSS Shortkeys WHERE SHORTKEY USEFUL FOR Data Editor CTRL + t Switch between data view and variable view. Data Editor CTRL +  /  […]

SPSS Toolbar Tool Building

Summary A previous tutorial covered assembling your own toolbar. This will become even more interesting if you add your own toolbar tools to it. This tutorial quickly walks you through and suggests some best practices. 1. Create a Folder with Syntax and Images Setting Up your SPSS Toolbar Tools Like so may Speed Things Up […]

SPSS Toolbar Building

Summary Toolbars can be very useful in SPSS. They allow users to do a lot of stuff with a single mouse click. However, some users may feel there’s some limitations to their default configuration. An ideal way to get around these is to assemble your own toolbar. Some limitations of standard toolbars Most users will […]

SPSS Dictionary

It’s not informative that “a respondent has 0 on v1” unless you know what v1 and 0 refer to. Such information – what the data actually represent – is collectively know as the dictionary. This tutorial merely explains what the SPSS dictionary is. For learning how to modify it properly (that is, by syntax), see Changing Variable Properties 1 – Introduction. SPSS Dictionary – What is […]