Function declaration style and variable scope problem

package sample
{
  import mx.binding.utils.BindingUtils
  import mx.containers.HBox
  import mx.controls.Alert
  import mx.controls.CheckBox
  import mx.core.IFactory
 
  import flash.events.Event
 
  public class CheckboxListRenderer extends HBox {
 
    [Bindable]
    public var listRenderer:IFactory
 
    public var checkbox:CheckBox = new CheckBox()
 
    private var instance:*
 
    private var checkboxChange = function(event:Event):void {
      if (data.hasOwnProperty('selected')) {
        data.selected = checkbox.selected
      }
    }
 
    public override function set data(item:Object):void {
      super.data = item
      if (item && item.hasOwnProperty('selected')) {
        checkbox.selected = item.selected
      }
    }
 
    protected override function createChildren():void {
      super.createChildren()
      addChild(checkbox)
 
      if (listRenderer != null) {
        instance = listRenderer.newInstance()
        addChild(instance)
      }
      trace("Checkbox list renderer created children")
    }
 
    protected override function commitProperties():void {
      super.commitProperties()
      horizontalScrollPolicy = "off"
      verticalScrollPolicy = "off"
 
      // Handle change in targeting phase for changing data selected flag.
      checkbox.addEventListener(Event.CHANGE, checkboxChange)
 
      BindingUtils.bindProperty(instance, "data", this, "data")
    }
 
  }
}

    private var checkboxChange = function(event:Event):void {
      if (data.hasOwnProperty('selected')) {
        data.selected = checkbox.selected
      }
    }

    private function checkboxChange(event:Event):void {
      if (data.hasOwnProperty('selected')) {
        data.selected = checkbox.selected
      }
    }