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Hi there: I am trying to test a simple mediation model where a level2 predictor (w) is an exogenous variable and a level1 variable (y1) is the primary endogenous variable. Variables x1 and x2 (both level1 variables) are hypothesized to be mediators of this relationship. When I run the code below I get the following WARNING: ** WARNING in MODEL command In the MODEL command, the following variable is a yvariable on the BETWEEN level and an xvariable on the WITHIN level. This variable will be treated as a yvariable on both levels: X1 *** WARNING in MODEL command In the MODEL command, the following variable is a yvariable on the BETWEEN level and an xvariable on the WITHIN level. This variable will be treated as a yvariable on both levels: X2 However, despite this WARNING I do get an estimate of both the y1x1 and y1x2 relationship at the WITHIN level according to the output. Should I be worried, or is there a better way to specify this mediation model? VARIABLE: NAMES ARE y1 y2 x1 x2 w clus; USEV ARE y1 x1 x2 w; BETWEEN = w; CLUSTER IS clus; ANALYSIS: TYPE = TWOLEVEL; MODEL: %WITHIN% y1 ON x1 x2; %BETWEEN% x1 x2 ON w; 


It is just saying the x1 and x2 are being treated at dependent variables on both levels. This means distributional assumptions are made about them. If this is the model you want, this is how it is done. 


Hello, I am running a similar multilevel mediational path model [per Preacher et al (2011), a 211 model], yet with a 4level categorical (ordinal) outcome (i.e. y1 above is ordinal). Mplus does not seem to allow this, with the message: *** ERROR in MODEL command Observed variable on the righthand side of a betweenlevel ON statement must be a BETWEEN variable. Problem with: x1 Same message repeated for any mediating variables with both within and between level components. Running with the outcome as continuous does work. Is there a different setup required, or is the multilevel ordinal logistic model with mediation impossible to test with Mplus? I realize the numerical integration makes it computationally problematic, but Mplus won't try to run it. Thanks, Phil 


Try running it in WLSMV. If that doesn't do it, try putting a factor behind x1 and let that factor be on the righthand side of the betweenlevel ON. 


Thanks Dr. Muthen. The workaround of creating the perfect factors separating within/between components did work. As a followup question, I wonder if Mplus is able to model a weighted TWOLEVEL model with an ordinal outcome and mediators using MLR, to obtain an ordinal logistic model. The model runs using WLSMV but not with MLR, and I receive this error: THE ESTIMATED WITHIN COVARIANCE MATRIX COULD NOT BE INVERTED. COMPUTATION COULD NOT BE COMPLETED IN ITERATION 1. CHANGE YOUR MODEL AND/OR STARTING VALUES. THE MODEL ESTIMATION DID NOT TERMINATE NORMALLY DUE TO AN ERROR IN THE COMPUTATION. CHANGE YOUR MODEL AND/OR STARTING VALUES. The chapter 16 tables of estimators seems to indicate the MLR should work, but perhaps I've set this up incorrectly. I'd appreciate any suggestions you might have. The following post will show a simplified model that yields the error. 


Here is the setup I've tried: VARIABLE: USEVARIABLES = wt cl_num ord1 cl_trt med1; CLUSTER = cl_num ; WEIGHT = wt ; WTSCALE = unscaled ; CATEGORICAL = ord1 ; BETWEEN = cl_trt ; ANALYSIS: TYPE = TWOLEVEL ; ESTIMATOR = MLR ; MODEL: %WITHIN% ! create perfect factors to separate within component ! (enables model to run, per suggestions from BM, KP) med1_w by med1@1; med1@0; ! within model statements ord1 ON med1_w ; %BETWEEN% ! create perfect factors to separate between component ! (enables model to run, per suggestions from BM, KP) med1_b by med1@1; med1@0; ! mediator relationship med1_b ON cl_trt(a); ! outcome relationships ord1 ON med1_b(b); ord1 ON cl_trt; MODEL CONSTRAINT: ! indirect effect NEW(ie1); ie1=a*b ; ! Between indirect 


Try med1@0.01; If that doesn't help, send materials to support. 


Thanks Dr. Muthen, adding back that little bit of variance allowed the model to work under MLR. I appreciate your prompt suggestions. Very best regards, Phil 

Andy Luse posted on Wednesday, August 01, 2012  11:08 am



I have a 121 mediation model where the two within IVs (rotate, healthy) are dicotomous, the 2nd level mediator is latentcontinuous (Imp), and the 1st level DV (choice) is also dichotomous. I am trying to test for indirect effects for each of the two IVs through the mediator. I tried using your suggestions above, but I get the same error when setting @0 and when I set it @0.01 it just keeps running. 

Andy Luse posted on Wednesday, August 01, 2012  11:11 am



Here is the syntax... USEVARIABLES ARE id choice rotate healthy Imp_1 Imp_2 Imp_3 Imp_4 Imp_5 Imp_7 Imp_9; CLUSTER IS id; BETWEEN ARE Imp_1 Imp_2 Imp_3 Imp_4 Imp_5 Imp_7 Imp_9; CATEGORICAL = choice; ANALYSIS: TYPE IS TWOLEVEL; ESTIMATOR = MLR; MODEL: %WITHIN% e1_w BY rotate@1; rotate@0; e2_w BY healthy@1; healthy@0; e1_w WITH e2_w@0; choice ON e1_w e2_w; %BETWEEN% Imp BY Imp_1 Imp_2 Imp_3 Imp_4 Imp_5 Imp_7 Imp_9; e1_b BY rotate@1; rotate@0; e2_b BY healthy@1; healthy@0; e1_b WITH e2_b@0; Imp ON e1_b(a_1); Imp ON e2_b(a_2); choice ON Imp(b); choice ON e1_b; choice ON e2_b; MODEL CONSTRAINT: NEW(indb_1); indb_1 = a_1 * b; NEW(indb_2); indb_2 = a_2 * b; OUTPUT: TECH1 TECH8 CINTERVAL; 


Please send the two outputs and your license number to support@statmodel.com. Please keep your posts to one window. 

Andy Luse posted on Friday, August 03, 2012  10:06 am



Ok, I have broken it down to where I am just trying to estimate the direct effect at each level with a single dichotomous IV (rotate) and a single dicotomous DV (choice), but I get the error "THE ESTIMATED WITHIN COVARIANCE MATRIX COULD NOT BE INVERTED. COMPUTATION COULD NOT BE COMPLETED IN ITERATION 1. CHANGE YOUR MODEL AND/OR STARTING VALUES." I'm trying to use the method above. %WITHIN% e1_w BY rotate@1; rotate@0; choice ON e1_w; %BETWEEN% e1_b BY rotate@1; rotate@0; choice ON e1_b; 


There is no difference between saying %WITHIN% e1_w BY rotate@1; rotate@0; choice ON e1_w; or choice ON rotate; Use the second approach. 

Andy Luse posted on Friday, August 03, 2012  12:20 pm



When I change the within section to choice on rotate I get "SERIOUS PROBLEM IN THE OPTIMIZATION WHEN COMPUTING THE POSTERIOR DISTRIBUTION. CHANGE YOUR MODEL AND/OR STARTING VALUES." 


You should change within and between in the same way. 

Andy Luse posted on Friday, August 03, 2012  2:26 pm



When I try that, I get the following error and it doesn't run "Unrestricted xvariables in TWOLEVEL analysis with ALGORITHM=INTEGRATION must be specified as either a WITHIN or BETWEEN variable. The following variable cannot exist on both levels: ROTATE" 


With numerical integration, the latent variable decomposition of a individual variable is not allowed. You need to create a betweenlevel variable for rotate. You can do this using the CLUSTER_MEAN option of the DEFINE command. 

Andy Luse posted on Saturday, August 04, 2012  12:21 pm



Ok, I made a new clusterlevel variable for rotate using the CLUSTER_MEAN command and then specified rotate as a within variable and the new variable (rotate_b) as a between variable. Now I am getting the following error... *** ERROR One or more variables have a variance of zero. Check your data and format statement. Continuous Number of Variable Observations Variance CHOICE 864 0.000 ROTATE 864 0.250 **ROTATE_B 864 0.000 I'm not sure why choice is listed as a continuous variable as I have specified it as categorical in the variable portion. It makes sense that rotate_b would have a variance of zero as it is the mean of the within subjects dichotomous experimental condition rotate. 


You will need to send this to support. It is not possible to diagnose it without further information. 

Andy Luse posted on Monday, August 06, 2012  9:42 am



Does this mean I'll need to purchase a new support contract? 


If you don't have an uptodate support contract, you are not eligible for support. 


Hello, Suppose 221 multilevel mediation model for about 400000 patients in 300 hospitals in 9 countries. Random intercepts for the hospital, no random slopes. Countries are not chosen at random and n is only 9. One possibility is multiple group (i.e. country) multilevel (i.e. hospital) mediation model, which for these data is too computationally demanding. I have also not seen examples of this in the literature. An often suggested proxy is to put country in as a fixed effect. In a mediation model, would country then have to be included in both the a as well as the b path? CLUSTER = hosp; BETWEEN = ctrptn ctreduc pes beds0 bedsmiss tech0 techmiss teac0 teacmiss clinical country; WITHIN = age sex er drg ermiss charlson; CATEGORICAL = d30; analysis: TYPE= twolevel; ESTIMATOR = BAYES; BITERATIONS = (1000); PROCESS=2; model: %BETWEEN% d30 on ctrptn ctreduc beds0 bedsmiss tech0 techmiss teac0 teacmiss country; d30 on clinical (b); clinical on ctrptn (a); clinical on pes country; %WITHIN% d30 on age sex er ermiss drg charlson; MODEL CONSTRAINT: NEW(ind); ind=a*b; 


Yes, seems right to me. 


Thanks for your help. I've included country dummy variables and findings are identical to those of a threelevel model. 


Does my code & calculation of the indirect effects look correct for specifying a sequential mediation model with all paths fixed? Thanks USEVARIABLES ARE ID X M2 M1 Y; MISSING ARE ALL (999); CLUSTER IS ID; !GROUPING VARIABLE IS ID WITHIN = X M2 M1;!LEVEL 1 VARIABLES BETWEEN = ; DEFINE: CENTER X M2 M1 (GROUPMEAN);!GROUP MEAN CENTER Analysis: TYPE = TWOLEVEL RANDOM; MODEL: %WITHIN% Y ON M1 (b1); !path b1 Y ON M2 (b2); !path b2 Y ON X (cdash); !Direct effect XY M1 ON X (a1); !path a1 M2 ON X (a2); ! path a2 M2 ON M1 (d1); ! path d1 %BETWEEN% Y; ! no predictors of intercept MODEL CONSTRAINT: NEW(a1b1 a2b2 a1d1b2); a1b1 = a1*b1; !Specific indirect effect of X on Y via M1 a2b2 = a2*b2; !Specific indirect effect of X on Y via M2 a1d1b2 = a1*d1*b2; !Specific indirect effect of X on Y via M1 and M2 OUTPUT: TECH1 TECH8 CINTERVAL; 


Looks ok. But I don't know why you groupmean center the mediator. 

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