Setting the Base Rate in the PADDS Pediatric ADHD Assessment Software Program

To be effective we must first determine the correct base rate , or the initial risk that the patient has ADHD. The Base Rate is also known as Prevalence, or Pre-Test Probability. Establishing the proper base rate is important because it will have a dramatic effect on the Post-Test Probability.

The PADDS is set by default at a conservative base rate of 4%, which is consistent with the reported 95% confidence intervals, this however, should be adjusted to reflect your individual situation.

Currently reported base rates can range anywhere from 0.03 to 0.74. The higher estimates are from specialized ADHD clinics and the lower estimates are from recent epidemiological studies. Specialized neuropsychology clinics normally have higher base rates as a result of referral sources weeding out many of the more unlikely cases in advance, however, a solid rationale must exist for the use of these extremely high base rates. Whenever possible, the practitioner should calculate the base rate of ADHD based on literature review and the past history of their particular setting, and periodically update this to reflect changes in the population or individual client pool.

From the PADDS program main menu screen, follow the steps shown in the images below.

PADDS Documentation

• Setting the Base Rate
• Target Tests (TTEF)
• Information Handout(pdf)
• User Qualification Form(pdf)
• PADDS Brochure(pdf)
• Testimonials

PADDS Support

• PADDS Program FAQ
• PADDS Support FAQ
• PADDS Tutorials

Sample Reports(pdf)

• Cognitive Tests (TTEF)
• SNAP-IV Parent/Teacher
• Case Study Reports
• PADDS Scoring
• Bell Curve Psychometrics
• Diagnostic Interview(CADI)

PADDS Research

• Reliability & Validity
• ROC of PADDS
• Clinical Demographics
• Incremental Validity
• PADDS Report Features
• Target Test Development
• Clinical Manual Excerpt
• Research Opportunities
• Our Important Associates

In the example above, we use sample data from a specialty clinic. The calculated local base rate is 0.35. This is then input in the form below as shown, and click Apply to set it.

Do not attempt to change the Base Rate (Prevalence) until you are certain you understand what it is and how it will affect your test scores and outcomes. It is imperative to incorporate meaningful base rate information into the process of establishing incremental validity. The PADDS uses a conservative estimate of 4%, as a beginning base rate. When test scores fall below or above the 95% confidence interval, this default base rate is sufficient. However, the clinical referral population is usually higher than this estimate. To maximize the effectiveness of the PADDS, we established this mechanism, by which the actual base rate from an individual practice can be incorporated into the overall assessment process. This gives a more accurate rationale to the incremental validity of the PADDS scores, and to the improvement of the incremental validity of other sources of data that may rely on accurate base rate.

To calculate your actual base rate for ADHD, you must determine the percentage of patients, referred to you for ADHD assessment, who are then subsequently diagnosed as ADHD.
(i.e. out of 100 patients, 34 are positive for ADHD = 34% base rate). This may need to be recalculated periodically to reflect changes in the referral population.

There is more information in the manual and on our website covering more in-depth aspects of the Evidence-Based Assessment.
Check back often.