Hi everyone, If anybody could give some advice you'd be my life saver. I measured three variables in an online questionnaire. One with the Likert scale, one with a modified Likert scale with 6 levels and one, the NPI-15 as a forced-choice format with dichotomous answers to each item. I wanted to analyze the relationship between the variables using a multiple regression analysis in SPSS. Now for the NPI, you normally simply calculate the grand sum for evaluation, since every item can give 1 or 0 points, depending on the choice, the max. would be 15. Is it even possible to compare two variables that have been measured using a Likert scale (the variable gets calculated using the MEAN function in SPSS) to one with a forced-choice-format (the variable gets calculated using the SUM function in SPSS)? Or could I just calculated the mean for the NPI-15 anyway despite of the format used in collecting the data? Or will this mess up my data? This is my first time working with SPSS, please be kind if my question is super dumb.