Redirect parameters from form values

I feel I've read through a lot of previous posts about redirect variables, but still cannot find a solution to passing a parameter value from a form field.

I've tried the options below and still cannot pull what I need from the form values. What am I missing?

Parameters:
variable = $form->data['continue']
variable = {$form->data['user_id']}
variable = {data['user_id'}

Thank you!