Setting the selected list box control item from another list box

I have a list box control with 3 options. This control updates several different bar charts in my Axiom application. As the user scrolls to see the other bar charts, they don't see the list box control anymore. I copied the list box allowing them to change it in several different places as they scroll. However, if they scroll back up to a previous copy of that list box control, it won't show the same value. I tried setting the selected item of list box 1 from list box 2 but I didn't have luck with this. Has anyone done this where you could give me your scripting line?

Example: 

This works fine to get the selected value and use it to update a label:

if (selectedItems[0]=="% of time") LBL_ByPeriod.Text = "% of time By Period (672 hours)";

I don't know though how to do something like this:

public void LB_ChartAgg_OnSelectionChange(object sender, string[] selectedItems)

if (selectedItems[0]=="% of time") LB_ChartAgg2.selectedItems[0] = "% of time";