Conjoint Analysis SPSS Syntax: A Complete Step-by-Step Tutorial
Conjoint analysis is one of the most powerful market research techniques available to researchers today. It helps you understand exactly how consumers make trade-off decisions between product features. However, many SPSS users do not realise that conjoint analysis SPSS syntax is the only way to run this procedure. There is no graphical user interface (GUI) for it. You must enter the CONJOINT command directly into a syntax window and execute it manually. Therefore, this tutorial walks you through every stage – from generating the orthogonal design to interpreting utility scores – with clear syntax examples at each step. Whether you are studying consumer preferences, designing surveys, or conducting academic research, mastering conjoint analysis SPSS syntax will unlock a level of analytical depth most researchers never reach. What Is Conjoint Analysis? Conjoint analysis is a market research tool for developing effective product design. Using it, researchers can answer questions such as: What product attributes matter most to the consumer? Which combination of features drives the highest preference? The core idea is simple but powerful. Instead of asking respondents which single feature they prefer, conjoint analysis asks them to evaluate complete product profiles. Each profile contains multiple attributes at the same time. For example, imagine evaluating an airline ticket. You might choose between a cramped seat at $225 with a direct flight, or a spacious seat at $800 with a layover. Each option involves a trade-off. Conjoint analysis captures exactly how respondents weigh those trade-offs against each other. Running conjoint analysis in IBM SPSS Statistics is only available via SPSS syntax, making it essential to understand every subcommand before you begin. For researchers already comfortable with SPSS, exploring what data analysis tools are available helps contextualise where conjoint fits within the broader analytical toolkit. The Three Stages of Conjoint Analysis in SPSS There are three stages to running a conjoint analysis procedure in SPSS: Each stage depends on the one before it. Therefore, follow this sequence carefully. Skipping or rushing any stage will produce invalid results. Stage 1: Generate an Orthogonal Design What Is an Orthogonal Array? When you have multiple product attributes and several levels for each, the total number of possible combinations explodes very quickly. Asking respondents to evaluate all combinations is impractical. To solve this, conjoint analysis uses a fractional factorial design. The resulting set, called an orthogonal array, captures the main effects for each factor level using only a fraction of all possible combinations. Interactions between factor levels are assumed to be negligible. The Generate Orthogonal Design procedure creates an orthogonal array and is typically the starting point of a conjoint analysis. Steps to Generate the Design From the SPSS menu, go to Data > Orthogonal Design > Generate. Then: What Are Holdout Cases? Holdout cases are judged by the subjects but are not used when the Conjoint procedure estimates utilities. Instead, they serve as a check on the validity of the model. They are generated from a separate random plan, not from the main orthogonal design, and do not duplicate any experimental profiles. This is an important quality check. In many conjoint analyses, the number of parameters is close to the number of rated profiles, which can inflate correlations artificially. Holdout correlations therefore, give a more realistic measure of model fit. Once the design is saved, you can display it using Data > Orthogonal Design > Display to produce formatted profile cards for presenting to respondents. If you are collecting data for this stage through structured surveys, see our guide on market research surveys for best practices on designing effective data collection instruments. Stage 2: Collect and Prepare Your Data Three Methods of Data Recording Once respondents evaluate the profile cards, you record their responses in one of three ways. The method you choose determines which subcommand you use in your conjoint analysis SPSS syntax. You must specify one, and only one, of these subcommands in every CONJOINT command. Typical Sample Sizes The sample size in commercial conjoint studies usually ranges from 100 to 1,000, with 300 to 550 being the most typical range for commercial studies. Smaller academic studies often use fewer than 100 respondents, but the sample should always be large enough to ensure reliability. Preference data should be stored in a separate .sav file from the plan file. For example, your plan file might be named carpet_plan.sav, and your preference data file might be named carpet_prefs.sav. Before running the analysis, ensure your dataset is clean and complete. Read our detailed guide on how to delete missing data in SPSS to prepare your preference data properly before running the syntax. Stage 3: Running the Conjoint Analysis SPSS Syntax Opening the Syntax Window A graphical user interface is not available for the Conjoint procedure. To run it, you must go to File > New > Syntax in SPSS to open a syntax window. Type your CONJOINT command there, highlight it, and click the Run button (the right-pointing triangle on the toolbar). The Minimal CONJOINT Syntax The Conjoint procedure requires two files – a plan file and a data file – along with one data recording subcommand. The minimal specification looks like this: CONJOINT PLAN=’CPLAN.SAV’ /DATA=’RUGRANKS.SAV’ /SEQUENCE=PREF1 TO PREF22. Here, CPLAN.SAV is your plan file containing the orthogonal design, and RUGRANKS.SAV is your preference data file. PREF1 TO PREF22 identifies the preference variables covering all 22 profiles. You can also use an asterisk (*) to indicate the active dataset in place of a filename. For example: CONJOINT PLAN=’CPLAN.SAV’ /DATA=* This uses the currently open dataset as the preference data. However, you cannot use the asterisk for both the plan file and the data file simultaneously. The SUBJECT Subcommand If your data file contains multiple respondents, you must use the SUBJECT subcommand to identify each one. Without it, SPSS assumes all cases belong to a single subject. CONJOINT PLAN=* /DATA=’RUGRANKS.SAV’ /SCORE=SCORE1 TO SCORE22 /SUBJECT=ID. Here, the variable ID identifies each respondent. This is essential for computing individual-level utility scores and averaging importance values across subjects. The FACTORS










