Reading Continuous Performance Test (CPT) Results in ADHD Assessment: What Omission and Commission Errors Really Mean

When the Numbers Don't Tell the Whole Story

If you work with attention concerns, you know the moment well: a continuous performance test (CPT) report lands on your desk, a few values flagged in red, and a client whose presentation doesn't map neatly onto any of them. Whether the referral is a school-age child, an adolescent, or one of the rapidly growing number of adults questioning their attention, computerized measures like Conners' CPT, the TOVA, IVA-2, or QbTest are among our most useful tools — and also among the easiest to misread.

The questions that come up in supervision are almost always the same. "Inattention looks normal, but commission errors are elevated — is this really ADHD?" "My client's anxiety is high; how do I know the commission errors aren't just that?" These are exactly the right questions to ask. Moving past the flagged number to the neuropsychological mechanism underneath it is where the clinical skill lives.

This article unpacks the two error types at the heart of every CPT — omission errors and commission errors — and offers a concrete framework for folding that interpretation into your assessment and treatment planning.

What Each Error Type Is Actually Measuring

At their core, CPTs index two capacities: sustained attention and impulse control. But the more useful move is to reconstruct what was happening in the client's information processing during the task, rather than reading the score at face value.

Omission errors: inattention, or delayed processing?

An omission error occurs when the target appears and the client fails to respond. Traditionally this signals inattention — but clinically it can mean several different things:

• Lowered arousal. When the brain's arousal system isn't adequately engaged, targets simply slip past. This is common in the predominantly inattentive presentation, where there's little outward hyperactivity to tip you off.
• Slow processing speed. The client registers the stimulus but takes too long to convert recognition into a motor response, missing the window. This pattern also shows up in depression and in clients with a sluggish cognitive tempo (SCT) — so omission errors are not ADHD-specific.

Commission errors: impulsivity, or anxiety?

A commission error occurs when the client presses for a non-target. These correlate strongly with impulsivity and hyperactivity:

• Disinhibition. Weak inhibitory control — a frontal executive function — leaves the client unable to withhold a prepotent response. This is the textbook ADHD pattern.
• Anxiety-driven over-arousal. Here's the catch: highly anxious clients can also produce elevated commission errors. A "I can't get this wrong" mindset drives over-responding and over-correction. A high commission score, on its own, is not enough to land on an ADHD diagnosis.

A Differential Interpretation Guide

In practice the two error types combine in different ratios, or one stands out sharply on its own. The table below is meant to sharpen your differential diagnosis as you read a profile.

Table 1. Clinical comparison of omission and commission errors

Turning Data Into Intervention

A test result is a starting point, not a conclusion. Three strategies help you carry CPT findings into the work itself.

1) Read reaction-time variability, not just error counts

Don't stop at the number of errors — look at the standard deviation of reaction time. Even when error scores fall within the normal range, large RT variability (an erratic, up-and-down response pattern) signals that the client is burning excess effort to hold attention together. These clients fatigue easily in daily life and may start a session focused, then deplete rapidly. That tells you something the error count alone never would.

2) Use error patterns for feedback and psychoeducation

Reciting numbers to a parent or client mostly activates defensiveness. Instead, translate the error into behavior:

• "It isn't that they won't stop — it's that the brakes (the commission-error system) are a little loose, so even when they want to stop, the stop doesn't quite catch."
• "The spacing-out isn't weak willpower — it's that the antenna taking information in (the omission-error system) drops the signal for a moment."

Metaphors like these build rapport and shift a parent from blaming the child toward seeing someone who needs support.

3) Match the intervention to the dominant error type

For an omission-dominant profile, prioritize cueing strategies — auditory and visual prompts that re-orient attention — and break tasks into short, manageable segments. For a commission-dominant profile, lead with CBT-style "Stop & Think" training and relaxation work that slows an impulsive response tempo. Tailoring the plan to the error signature is what makes the data clinically useful.

Holding the Whole Picture

An ADHD formulation is never the CPT alone. It integrates developmental history, interview behavior, collateral report, and the test data into a single, expert judgment. The decisive moments often come when the test and the interview disagree — a normal-range profile in a child who is visibly distractible at school — and that's precisely where your clinical intuition and a careful review of the initial intake record earn their keep.

The most accurate reading comes from connecting the objective data to the lived clinical picture. When the two are held together rather than read in isolation, the assessment stops being a set of flagged numbers and becomes the beginning of a plan your client can actually use.