SOLAS 4.0 New Features

New Multiple Imputations Methods

• Mahalanobis Distance Matching Method
  The Mahalanobis distance is used in this method to identify fully observed cases that have similar characteristics to cases that have missing values. Missing data are filled in by sampling from the fully observed cases that are closest to the case with missing values. The multiple imputations are independent repetitions drawn from the range of closest cases.
• Predictive Mean Matching Method
  This method applies Ordinary Least Squares Regression for estimating predicted values for each case in the dataset. Rather than using the predicted values for the imputation, they are used to identify similarities between cases with missing values and fully observed cases. Cases are sorted in to Donor Pools and similar to the Mahalanobis Distance method, imputations are drawn from these pools.
• Propensity Score/Predictive Mean Matching/Mahalanobis Distance Combination Method
  The Propensity Score method and Predictive Mean Matching method described above are both applied to the data set. This results in each case in the data set having a propensity score and predicted value associated with it. These are then used as covariates and the Mahalanobis Distance method is applied to find cases that can be used to impute missing values.

New Graphics

• Collapse Missing Data Pattern
  There is a new option to collapse the SOLAS missing data pattern. This option looks at the pattern of missing and observed variables for each case and displays the various patterns that occur inthe data, indicating how many times that paticular pattern occurs.
• Pre & Post Imputation Graphics
  The new Marginplot can be used to plot variables that contain missing values. Values observed for both variables form a standard scatterplot. Additional boxplots along the X and Y axes give details about values that are not observed for both variables.
  After imputation it is useful to see the spread of the values that were imputed. This can be seen by using the new Scatterplot option in the Plot menu. This can be done from any of the imputed datapages.

64-bit Application

SOLAS 4.0 is available as a 32 or 64-bit application allowing for the use of larger data sets at faster processing speeds.