To ensure that we can compare the two models, we list the independent variables of both models in two separate blocks before running the analysis. When estimating a regression model including interactions, we first estimate a main effects multiple regression model.
#SPSS CODE INTERACTION HOW TO#
Screenshots for the procedure to produce histograms in SPSS are available in the How to Guides for the Dispersion of a Continuous Variables topic that is part of SAGE Research Methods Datasets. Click Continue to return to the previous dialog box and then click OK to perform the analysis.
For this example, just check “Histogram” under the Descriptive heading. This opens another dialog box where you can select the plots you want to produce. In the “Explore” dialog box that opens, move the immigration, trust and conformity variables into the Dependent List: box. A high score means positive feelings towards immigration, high levels of trust in people around, and high relative importance placed on values of conformity.Īnalyze → Descriptive Statistics → Explore They can all be regarded as continuous, with means of approximately zero and an approximate range of about −2.0 to +2.0 for immigration, −2.7 to +2.0 for trust, and −3 to + 3 for conformity. All three variables are centred about the mean. An individual’s mean score across all human values items was subtracted from their mean score on the items relating to the concept in question, thus identifying the priority placed on this particular value in relation to others. The variable conformity was compiled using items identified by the European Social Survey as relating to that value. Score variables for immigration and trust were constructed using a summative scale of selected survey items, tested for internal consistency. Score on a scale measuring strength of importance respondent placed on values of conformity in relation to nine other basic human values (conformity).Score on a scale measuring respondent level of trust in other people (trust).Score on a scale measuring how beneficial UK respondents feel immigration is to Great Britain (immigration).This example uses three variables from the 2016 European Social Survey: It is possible to have three-way interactions or more, but we focus on the two-way case for ease of explanation.Ģ An Example in SPSS: Attitudes to Immigration, Trust, and Conformity in Great Britain This example will focus on interactions between one pair of variables that are both continuous in nature. An interaction can occur between independent variables that are categorical or continuous and across multiple independent variables. In a linear regression model, the dependent variables should be continuous. Focus is given instead to the difference in slopes which is described by the interaction coefficient. In a model including an interaction term, the slope estimates cannot be interpreted in the same way, as they are now conditional on other values. Most attention is focused on the slope estimates because they capture the relationship between the dependent and independent variables. This requires estimating an intercept (often called a constant) and a slope for each independent variable that describes the change in the dependent variable for a one-unit increase in the independent variable. In a “main effects” multiple regression model, a dependent (or response) variable is expressed as a linear function of two or more independent (or explanatory) variables. Interaction describes a particular type of non-linear relationship, where the “effect” of an independent variable on the dependent variable differs at different values of another independent variable in the model.