That's actually a bad control group; you want some group whose lifestyle, including lifestyle changes, matches pretty well the rest of society but for exposure to the kind of radiating devices at issue, to isolate changes due to the effects of the devices at issue from the effects of other lifestyle changes.

Since the Amish lifestyle and lifestyle changes over the time period of interest don't match the general public in ways other than cellphone/wifi exposure, they aren't really a good control.