In my opinion their are no satisfactory screening tests for ADHD
particularly in adults. The ones that are used generally rely upon
apriori decisions as to exactly what the problem is in ADHD rather than
empirical correlations between test design and real world problems.
Chances are if you use a screening test to select your study group that
you will isolate a sub-population of adults that have a psychiatric
problem that shares some of the features of ADHD but that doesn't
represent most common etiological origens of the disease. Testing as it
is used now is to supplement the diagnosis arrived at from a structured
interview and to help weed out complicating or misleading comorbities
like other learning disabilities.
I suggest several things. Read the section on diagnosis of ADHD in the
Book "Driven to Distraction". It should be available in most large
bookstores and libraries. It briefly goes over the more commonly used
tests and tells in general terms why they are poor screening devices.
Follow-up on the diagnostic references listed in there. Contact
psychiatrists in your area that specialize in learning disabilities in
adults and ask them if they would tell their patients that there is a
need for research subjects with ADHD.
Most people with ADHD can focus in the highly structured environment of
traditional psychological tests. The problem becomes manifest only when
attentional priorities become less obvious and more demanding.