An Introduction to JASP: A Free and User-Friendly Statistics Package James E Bartlett 1 Introduction 1.1 What is JASP? JASP is a free, open-source alternative to SPSS that allows you to perform both simple and complex analyses in a user-friendly package. The aim is to allow you to conduct complex Classical (stuff with p values) and Bayesian statistics (outlined in section 8), but have the advantage of a drag-and-drop interface that is intuitive to use. 1.2 The development of JASP JASP is still in development with new features being added almost on a monthly basis. This means you should constantly be checking their Twitter (@JASPStats) or Facebook (JASPStats) accounts to see if there is a new version available. This guide currently supports the features available in version 0.8.6 (as of February 28, 2018). If this is slightly out of date and there is a new feature you are confused about, feel free to email me and remind me to update it. 1.3 Why JASP? Although many universities predominantly use SPSS, it is extremely expensive which means you probably cannot use it unless you are affiliated with a university, and even then the licensing means it is often a nightmare to use on your own computer. JASP is a free, open-source alternative that aims to give you a simple and user-friendly output, making it ideal for students who are still getting to grips with statistics in psychology. Here are just a few benefits of using JASP: 1.3.1 Effect sizes Effect sizes are one of the most important values to report when analysing data. However, despite many articles and an APA task force (1999...no one ever listens) explaining their importance, SPSS only offers a limited number of effect size options and many simple effect sizes are requiredtobe calculated manually. On the other hand, JASP allows you to simply tick a box to provide an effect size for each test, and even provides multiple options for some statistical tests. 1.3.2 Continuously updated output Imagine you have gone through all of the menus in SPSS to realise you forgot to click one option that you wanted to be included in the output. You would have to go back through the menus and select that one option and rerun the whole analysis, printing it below the first output. This looks incredibly messy and takes a lot of time. In JASP, all of the options and results are presented on the same screen. If you want another option to be presented, all you have to do is tick a box and the results are updated in seconds. 1.3.3 Minimalist design For each statistical test, SPSS provides every value you will ever need and more. This can be very confusing when you are getting to grips with statistics and you can easily report the wrong value as SPSS also has their own naming conventions (e.g. sig. instead of p value). In JASP, the aim is minimalism. You start off with the bare bones result, and you have the option to select additional information if and when you need it. 1 1.3.4 Reproducible analyses A large number of errors being reported in psychological research has led to calls to improve the reproducibility of research findings (Munafo et al. 2017). This means that you can show someone exactly how you got to the results you included in your report. In JASP, you have the opportunity to save your data and analyses together as a .jasp file. This preserves the analyses you performed to show yourself (thinking of your future self is probably the most important factor as even you will probably forget which options you selected) and others months or years after conducting the analyses. In SPSS, you can save the output file, but this relies on you reverse engineering allthe options that you selected, providing room for error if you miss one of the options. SPSS also creates unnecessary barriers to accessing data as you can not open .sav files without having a valid SPSS license. Therefore, your data would not be accessible to anyone who did not have access to SPSS. 1.4 Using JASP 1.4.1 How to download JASP JASP can be downloaded for free on their website for either Windows, OSX, or Linux (if that’s your thing). Installing it should be pretty straightforward, just follow the instructions it provides you. After installing it and opening the program, you will find the ”Welcome to JASP” window shown in Figure 1. Figure 1: The JASP startup window 1.4.2 Entering data in JASP The first difference you will find between SPSS and JASP is how you enter data. InSPSS,you enter data manually through the data view screen. In JASP, there is currently no facility to enter data directly, and you have to load the data after it has been created in a different program. JASP currently supports SPSS .sav files (this is useful if you already have data in SPSS as you donot need to use SPSS to view or analyse it), Excel .csv files, and Open Office .osd files. If youdatais a normal Excel Workbook (.xlsx), you first have to convert it to a .csv file. If you need tocreatea .csv file from a .xlsx file, here is a useful link that explains how to create one. One feature in JASP is what they call ’data synchronisation’. Although the data is still hosted as a .csv or a .sav file, you can double click on a data point in JASP and it will open the data file in either Excel, SPSS, or Open Office (the only downside to this is if you no longer have access to SPSS you wouldnotbe 2 able to edit the original data file). You can then make changes to the file and it will automatically update in JASP when you have saved it. For further details, see the JASP tutorial. To start any data analysis, we need to load some data to use. At the top of the ”welcome” window, there are two tabs: File and Common. Click on the File tab and you will see the window in Figure 2. Here you will have your recently opened files on the right if you have used it before, but yours should be blank the first time you use it. To open a file, click on Computer >Browse, then select the data file from wherever you saved it on your computer. After it has loaded, the ”welcome” window will look slightly different as your data will be visible on the left side ofthe window like in Figure 3. Figure 2: Opening a data file in JASP. You can choose from different files in your computer, or open a file directly from the Open Science Framework 1.4.3 Changing data types The next step is to make sure JASP knows what type of data your variables are (e.g. nominal, ordinal). Unlike SPSS, JASP does its best to guess what data type it is. The symbols at the top of the columns in Figure 3 look like three circles for nominal data, three lines like a podium for ordinal data, and a little ruler for scale data. Most of the time JASP gets it right and the columns have the right symbol. However, sometimes it is not quite right. If you click on the symbol, you can change it from one data type to another if things are not quite right. Another difference between JASP and SPSS is how you define nominal factor levels. InSPSS, you might remember that to define an independent groups factor such as nationality you needto assign each level a value and label. For example, you could list the first participant as German and label them with a 1, the second person could be Chinese and be assigned a 2. Every German participant would be identified by the number 1, and every Chinese participant would be labeled2 etc. However, in JASP you have the choice of using values as factor levels or using labels as factor levels. You just need to make sure the variable type is nominal (three little circles) at the top of the column. An important thing to note is that if you use labels, all of them need to be exactly the same to be considered the same condition throughout the dataset. For example, German could not be spelled as german or GERMAN, or JASP would think these are three different conditions. It has to be written exactly the same, capitals and spaces and everything. We will come back to creating a label for values in section 3.2.1. 3 Figure 3: An empty window with a data file loaded 2 Guide Organisation This guide currently covers three basic statistical tests: T-Tests, correlations, and ANOVA. The first part of this guide focuses on how these can be analysed using the classical approach tostatistics through the use of Null Hypothesis Significance Testing (NHST). The Bayesian equivalent of the T-Test is then introduced in section 7. Throughout the guide, the aim is to demonstrate show how basic analyses that you may be familiar with performing in other statistical packages can be performed in JASP, and offer some practical recommendations. There are some digressions where the topics are not usually discussed in normal textbooks such as using the Student or Welch’s T-Test, or outlining different types of effect size for ANOVA. However, the main focus isonthe process of performing the analyses, and not on the rationale and background to using them.