I cant change the combobox selection programmatically WPF C#

<pre><ComboBox x:Name="cbCostType" ItemsSource="{Binding}" SelectedValuePath="CostTypId" DisplayMemberPath="CostTypeName" Canvas.Left="176" Canvas.Top="118" Width="214" TabIndex="5" SelectionChanged="cbCostType_SelectionChanged"/>

<pre>public class CostType
    {
       public int CostTypeId { set; get; }
       public string CostTypeName { set; get; }

       public CostType(int costTypeId, string costTypeName)
       {
           this.CostTypeId = costTypeId;
           this.CostTypeName = costTypeName;
       }
    }

<pre> public static List<CostType> FillDriverCostTypeCombo()
        {
            var costList = new List<CostType>();
            var costIncluded = new CostType(0, "Included");
            costList.Add(costIncluded);
            var costMonth = new CostType(1, "Monthly");
            costList.Add(costMonth);
            var costDay = new CostType(2, "Daily");
            costList.Add(costDay);
            return costList;
        }

cbCostType.selectedValue=1;

var costTypeitem=new CostType(1,"monthly");
cbCostType.selectedItem=costTypeitem;