Mplus Users Guide v6.. - Muthén & Muthén

Special Modeling Issuesclass indicators, the threshold starting values for each variable must beordered from low to high. The exception to this is when equalityconstraints are placed on adjacent thresholds for a variable in which casethe same starting value is used. It is a good idea to start the classes apartfrom each other.Following is a translation of probabilities to logit threshold values thatcan be used to help in selecting starting values. Note that logit thresholdvalues have the opposite sign from logit intercept values. The probabilityis the probability of exceeding a threshold. High thresholds areassociated with low probabilities.Very low probability Logit threshold of +3Low probability Logit threshold of +1High probability Logit threshold of -1Very high probability Logit threshold of -3GROWTH MIXTURE MODELSIn most analyses, it is sufficient to use the default starting valuestogether with random starts. If starting values are needed, the followingtwo strategies are suggested. The first strategy is to estimate the growthmodel as either a one-class model or a regular growth model to obtainmeans and standard deviations for the intercept and slope growth factors.These values can be used to compute starting values. For example,starting values for a 2 class model could be the mean plus or minus halfof a standard deviation.The second strategy is to estimate a multi-class model with the variancesand covariances of the growth factors fixed at zero. The estimates of thegrowth factor means from this analysis can be used as starting values inan analysis where the growth factor variances and covariances are notfixed at zero.MULTIPLE SOLUTIONS FOR MIXTUREMODELSWith mixture models, multiple maxima of the likelihood often exist. Itis therefore important to use more than one set of starting values to findthe global maximum. If the best (highest) loglikelihood value is notreplicated in at least two final stage solutions and preferably more, it is413