diff --git a/src/classes/batchSegmentCreator.cls b/src/classes/batchSegmentCreator.cls
index 271634e..78ace3d 100644
--- a/src/classes/batchSegmentCreator.cls
+++ b/src/classes/batchSegmentCreator.cls
@@ -33,6 +33,7 @@ gglobal class batchSegmentCreator implements Database.Batchable<SObject>,Databas
 	global List<Id> segmentCampaignIds;
 	global List<Integer> segmentSizes;
 	global List<Integer> membersAdded;
+	global List<Double> sizesCDF;
 	global String errorTxt = '';
 	global boolean keepOriginal;
 	
@@ -57,7 +58,18 @@ gglobal class batchSegmentCreator implements Database.Batchable<SObject>,Databas
 	    	Boolean assigned = false;
 	    	
 	    	while(assigned == false){
-		    	Integer assignedList = Math.floor(segmentCampaignIds.size() * Math.Random()).intValue();
+	    		Integer assignedList;
+	    		Double prob = Math.Random();
+	    		
+	    		// iterate through sizesCDF to find correct bucket
+	    		// note that sizesCDF must be sorted from smallest to largest
+	    		// probability (and should be given the generation process above)
+	    		for (Integer i=0; i<sizesCDF.size(); i++) {
+	    			if (sizesCDF[i] >= prob) {
+	    				assignedList = i;
+	    				break;
+	    			}
+	    		}
 
 				if((membersAdded[assignedList] < segmentSizes[assignedList])){		    
 					 newCampaignMembers.add(
@@ -202,4 +214,4 @@ gglobal class batchSegmentCreator implements Database.Batchable<SObject>,Databas
 		System.AssertEquals(database.countquery('SELECT count()' +' FROM CampaignMember WHERE campaignId=\'' + mySegmentIds[1] + '\''), 100);
 	}
 	
-}
\ No newline at end of file
+}
diff --git a/src/classes/memberAssignment.cls b/src/classes/memberAssignment.cls
index 66adb32..92c2610 100644
--- a/src/classes/memberAssignment.cls
+++ b/src/classes/memberAssignment.cls
@@ -34,6 +34,8 @@ public with sharing class memberAssignment {
 	static List<Integer> members;
 	static List<CampaignMember> newCampaignMembers;	
 	static Boolean keep;
+	static Integer totalSize;
+	static List<Double> sizesCDF;
 	
 	public static boolean assignMembersNow(Id parentCampaignId, List<Id> segmentCampaignIds, List<Integer> segmentSizes, List<Integer> membersAdded, Boolean keepOriginal){
 		campId = parentCampaignId;
@@ -44,11 +46,31 @@ public with sharing class memberAssignment {
 		newCampaignMembers = new List<CampaignMember>();
 		
 		List<CampaignMember> oldMembers = [select id,campaignId, leadId, contactid from campaignMember where CampaignId = :campId];
+
+		// Figure out the fraction that should go into each list,
+		// then generate a cumulative distribution function to
+		// use in making the assignments
+		totalSize = 0;
+		for (Integer s : sizes) {
+			totalSize += s;
+		}
+
+		// Generate the CDF
+		sizesCDF = new List<Double>();
+		sizesCDF.add(1.0*sizes[0]/totalSize);
+		for (Integer i=1; i<sizes.size(); i++) {
+			sizesCDF.add(sizesCDF[i-1] + (1.0*sizes[i]/totalSize));
+		}
+		// be sure final value is 1.0, regardless of rounding issues:
+		sizesCDF[sizesCDF.size()-1] = 1.0;
+
 		
 		for(CampaignMember thisMember : oldMembers){
 		 	assignMember(thisMember);		    
 		}
-		system.debug('******newCampaignMembers = '+newCampaignMembers);
+		// This may be millions of records long in prod, probably not
+		// worth spitting out to the console every time.
+		// system.debug('******newCampaignMembers = '+newCampaignMembers);
 		if(!newCampaignMembers.isEmpty()){
 			try {
 				insert newCampaignMembers;
@@ -66,9 +88,20 @@ public with sharing class memberAssignment {
 	}
 			
 	private static void assignMember(CampaignMember thisCampaignMember){
-		Integer assignedList = Math.floor(semgmentIds.size() * Math.Random()).intValue();
-		
-		if((members[assignedList] < sizes[assignedList])){		    
+		Integer assignedList;
+		Double prob = Math.Random();
+
+		// iterate through sizesCDF to find first correct bucket
+		// note that sizesCDF must be sorted from smallest to largest
+		// probability (and should be given the generation process above)
+		for (Integer i=0; i<sizesCDF.size(); i++) {
+			if (sizesCDF[i] >= prob) {
+				assignedList = i;
+				break;
+			}
+		}
+
+		if(members[assignedList] < sizes[assignedList]){		    
 			 newCampaignMembers.add(
 			 	new CampaignMember(
 					CampaignId = semgmentIds[assignedList],
@@ -76,9 +109,7 @@ public with sharing class memberAssignment {
 					ContactId = thisCampaignMember.ContactId		
 			 	)
 			 );
-			 if(members[assignedList] < sizes[assignedList]){
-			 	members[assignedList]++;
-			 }
+			 members[assignedList]++;
 		} else {
 			assignMember(thisCampaignMember);
 		}
@@ -89,4 +120,4 @@ public with sharing class memberAssignment {
 	    
 	    
 	
-}
\ No newline at end of file
+}
diff --git a/src/classes/segmentsController.cls b/src/classes/segmentsController.cls
index 24f640f..4149ec8 100644
--- a/src/classes/segmentsController.cls
+++ b/src/classes/segmentsController.cls
@@ -208,6 +208,26 @@ public with sharing class segmentsController {
                     batchSegments.segmentCampaignIds = newCampaignIds;
                     batchSegments.segmentSizes = segmentSizes;
                     batchSegments.membersAdded = membersAdded;
+
+		    // Figure out the fraction that should go into each list,
+		    // then generate a cumulative distribution function to
+		    // use in making the assignments
+		    Integer totalSize = 0;
+		    for (Integer s : segmentSizes) {
+		    	totalSize += s;
+		    }
+		    
+		    // Generate the CDF
+		    List<Double> segmentSizesCDF = new List<Double>();
+		    segmentSizesCDF.add(1.0*segmentSizes[0]/totalSize);
+		    for (Integer i=1; i<segmentSizes.size(); i++) {
+		    	segmentSizesCDF.add(segmentSizesCDF[i-1] + (1.0*segmentSizes[i]/totalSize));
+		    }
+		    // be sure final value is 1.0, regardless of rounding issues:
+		    segmentSizesCDF[segmentSizesCDF.size()-1] = 1.0;
+		    
+		    batchSegments.sizesCDF = segmentSizesCDF;
+		    
                     batchSegments.keepOriginal = keepOriginal;
                     batchSegments.email = batchEmailNotification;
                     ID batchprocessid = Database.executeBatch(batchSegments);
@@ -565,4 +585,4 @@ public with sharing class segmentsController {
 
     }
     
-}
\ No newline at end of file
+}