

Testing a Mediation with Count data. 

Message/Author 


Hi, I want to test a mediation model, where IV and mediator are continuous and DV is a count variable. It was no problem to specify the model itself but unfortunately MPlus (6.1) cannot determine indirect effects when using count data (error: "BOOTSTRAP is not allowed with ALGORITHM=INTEGRATION."). Is there any workaround (f.e. with MODEL CONSTRAINT command), so I can test the assumed mediation effect formally? Thanks in advance, Sebastian 


In this situation you can use MODEL CONSTRAINT to define the indirect effect. 


Thank you for the quick response. I'm not sure if I did it correct, but I finally specified a constraint model with 4IV, 1 Med and 1 CountDV (see below). Is this the way you thought of? If possible, I additionally want to determine the overall mediation effect (med_total). According to Preacher & Hays (2008) the total indirect effect is the sum of the specific indirect effects. Unfortunately, they used the bootstrapprocedure to analyze indirect effects and they had several mediators, not several IVs. Do you think I can still apply this rule to the current model (like I have done)? Thank you very much, Sebastian Title: Mediation with model constraints 4 IV, 1 Med, 1 DV (count) Data: File is MPLUS3.dat ; Variable: Names are age sex type y2 y1 y3 x4 x1 x2 x3 m2 m1 sq2 sq3 sq1; usevariables are y1 m1 x1 x2 x3 x4; count is y1; analysis: estimator=ml; model: m1 on x1 (a1); m1 on x2 (a2); m1 on x3 (a3); m1 on x4 (a4); y1 on m1 (b); y1 on x1 x2 x3 x4; Model Constraint: new (med1 med2 med3 med4 med_total); med1 = a1*b; med2 = a2*b; med3 = a3*b; med4 = a4*b; med_total = med1+med2+med3+med4; output: samp; stdyx; tech1; 


This looks correct. 


Great. Thank you! 

Back to top 

