QbTest and Continuous Performance Test Results for ADHD: What They Mean

Your child sat in front of a computer for 15–20 minutes and pressed a button every time a specific shape or letter appeared. Now you've got a report full of "omission errors," "commission errors," "hit reaction time variability," and maybe a motion-tracking heat map. Welcome to continuous performance testing — one of the most misunderstood components of an ADHD evaluation.

What Continuous Performance Tests Measure

A continuous performance test (CPT) measures sustained attention and impulse control under standardized, low-stimulation conditions. The child watches a screen, responds to target stimuli (press when you see this), and withholds responses to non-targets (don't press when you see that). The test runs long enough — typically 15 to 20 minutes — to capture attentional fatigue and variability over time.

The most commonly used CPTs in clinical practice:

Conners CPT-3: Published by the same company that makes the Conners 4 rating scales. Targets appear on screen and the child presses the spacebar for every letter except "X." Produces scores for detectability, omissions, commissions, perseverations, and hit reaction time.

TOVA (Test of Variables of Attention): Uses geometric shapes as stimuli. Provides attention, impulsivity, reaction time, and variability scores across four quarters of the test.

QbTest: Combines a standard CPT with infrared motion tracking. A reflective headband tracks the child's head and body movement throughout the test, adding an objective hyperactivity measurement that rating scales can't provide.

Reading the Core Metrics

Omission Errors

An omission error occurs when the target appears and the child fails to respond. Omissions measure vigilance — how well the child maintains sustained attention over time. A high omission rate means the child is missing targets, either because their attention drifted or because they processed the stimulus too slowly to respond.

On standardized scoring, omission scores are compared to age-matched norms. Read the score and classification against the norms and interpretation stated for the specific test and QbTest parameter in the report.

Commission Errors

A commission error occurs when a non-target appears and the child responds anyway. Commissions measure impulsivity — the child's ability to inhibit a prepotent response. A high commission rate indicates the child is responding before fully processing the stimulus, pressing the button reflexively rather than waiting to confirm the target.

Hit Reaction Time and Variability

Average reaction time tells you processing speed. But the more clinically informative metric is reaction time variability — how consistent the child's response speed is across the test. A child with ADHD often shows highly variable reaction times: fast on some trials, very slow on others, with the variability increasing as the test goes on. This inconsistency is a hallmark of attentional fluctuation.

QbTest Motion Tracking

The QbTest's unique contribution is its hyperactivity measurement. The infrared camera records the distance, area, and frequency of head and body movements during the test. The report displays this as a motion plot — a visual map of movement activity compared to age-matched norms.

A child who was fidgeting, shifting in their seat, leaning forward and back, or rocking will produce a dense, expansive motion plot. A child who sat relatively still will show a tight, contained pattern. This gives evaluators objective hyperactivity data that doesn't depend on a rater's subjective impression.

Why a "Normal" CPT Doesn't Rule Out ADHD

This is the most important thing to understand about CPT results: a normal score does not mean your child doesn't have ADHD. There are three well-documented reasons:

The testing environment is artificial. A quiet room, one-on-one attention, a novel computerized task, and a short duration create conditions that naturally boost focus — especially for children with ADHD, who often perform better with novelty and external structure. The real challenge isn't focusing for 15 minutes on a computer game. It's sustaining attention during a 45-minute lecture while 25 other children move around the room.

Cognitive ability compensates. Children with average-to-high IQs can use their cognitive reserves to power through a brief CPT, scoring within normal limits despite having genuine daily attention deficits. The test captures a snapshot of peak performance under ideal conditions, not typical performance under normal classroom demands.

CPTs have moderate sensitivity. The research reports sensitivity and specificity in the range of 60–70%, meaning a substantial percentage of children with confirmed ADHD will score normally. A normal CPT result simply cannot rule out an ADHD diagnosis when multi-informant rating scales, clinical interviews, and real-world impairment data point the other direction.

Clinical guidelines from the AAP, NICE, and CADDRA all state that CPTs are supplementary tools — they add information when abnormal, but a normal result doesn't override other evidence. If a school team or clinician tells you the CPT was "normal, so it's not ADHD," that's not consistent with current diagnostic standards.

When CPT Results Are Abnormal

Abnormal CPT results — high omissions, high commissions, and elevated variability — provide performance data that complements rating scales and other evaluation information. They do not establish ADHD or school eligibility on their own.

QbTest is integrated into select NHS ADHD pathways in the UK and has FDA clearance in the US. If your child's QbTest shows elevated Attention or Hyperactivity metrics, those are objective performance measures to consider alongside the rest of the clinical evaluation; they do not establish ADHD by themselves.

The ADHD Rating Scale Decoder explains how CPT results fit alongside rating scale data in the overall evaluation — and how to use both together when presenting your child's case to the school team or prescribing clinician.