External Data (Sharepoint List) - Percentage values importing as integer

Hi,

I'm pulling external data from a Sharepoint list into Visio. Integers are displaying perfectly, but percentage values are showing as integers. 

For example, 100% in Sharepoint shows as 1 in the External Data table. 50% shows as 0.5.

I can't see a way of changing this column to be percentage.

Any help appreciated!