Calculating a date field based upon the selection of a picklist

var years = 0;
switch(crmForm.all..DataValue) {
    //You need to check the picklist values if they have the values 1, 2 and 3. Look at the attribute in the entity customization and note the option values.
    case "1":
        years = 1;
        break;
    case "2":
        years = 2;
        break;
    case "3":
        years = 3;
        break;    }
if (years != 0) {  
    var date = new Date();
    date.setYear(date.getYear() + years);
    crmForm.all..DataValue = date; }