Cognitive Test ADHD Risk Assessment Methodology
Our cognitive tests (Go/No-Go and CPT-Lite) use a clinical-grade methodology to assess ADHD risk based on performance metrics. This page explains how we calculate risk using standardized clinical norms and weighted indices, similar to professional assessments like QBTest, Conners CPT, and TOVA.
Clinical-Grade Approach
Our methodology uses the same principles as professional clinical assessments:
- Standardization against established clinical norms
- Z-score transformation for each metric
- Weighted composite indices based on research
- Interpretation bands aligned with clinical standards
Overview of Our Cognitive Tests
Go/No-Go Task
Measures response inhibition and impulse control. Participants respond to "Go" stimuli (green circles) and inhibit responses to "No-Go" stimuli (red squares).
Focus: Inhibition, timing consistency, speed-accuracy trade-offs
CPT-Lite (X Task)
Measures sustained attention and vigilance. Participants respond only when the letter "X" appears, ignoring all other letters.
Focus: Sustained attention, vigilance, reaction time consistency
Step 1: Clinical Norms
We use established clinical norms (means and standard deviations) for adult CPT performance. These norms are based on conservative estimates from CPT research literature and represent typical performance for neurotypical adults.
Adult CPT-Lite Clinical Norms
| Metric | Norm Mean | Norm SD | Direction |
|---|---|---|---|
| Accuracy | 99% | 1.5% | Lower = worse |
| Reaction Time Variability (RTV) | 40 ms | 15 ms | Higher = worse |
| Omission Errors | 2 | 2 | Higher = worse |
| Commission Errors | 2 | 2 | Higher = worse |
| Performance Decrement | 1% | 2% | Higher = worse |
| Mean Reaction Time | 450 ms | 80 ms | Slower = worse |
These norms are conservative and consistent with CPT research literature. Actual clinical assessments may use proprietary norms.
Step 2: Z-Score Standardization
For each metric, we calculate a z-score to measure how far your performance deviates from the clinical norm:
z = (observed − norm_mean) / norm_SD
Example: If your accuracy is 95% and the norm is 99% with SD of 1.5%:
z_AccuracyLoss = (99 − 95) / 1.5 = 2.67
Important: Negative z-scores (performance better than normal) are clamped to 0. This means we only consider deviations that indicate risk—no "credit" for being better than typical.
Step 3: Weighted ADHD Risk Index
The z-scores are combined using research-based weights that reflect the relative importance of each metric for ADHD assessment. Different weights are used for Go/No-Go vs CPT-Lite, reflecting their different cognitive demands.
Go/No-Go Weights
Go/No-Go emphasizes inhibition and timing consistency:
- • Reaction Time Variability: 40%
- • Commission Errors (Inhibition): 25%
- • Accuracy Loss: 15%
- • Omission Errors: 10%
- • Mean Reaction Time: 10%
- • Performance Decrement: 0% (omitted)
CPT-Lite Weights
CPT-Lite emphasizes vigilance and sustained attention:
- • Reaction Time Variability: 35%
- • Omission Errors (Inattention): 30%
- • Performance Decrement: 15%
- • Accuracy Loss: 10%
- • Commission Errors: 5%
- • Mean Reaction Time: 5%
Calculation Formula
ADHD_RISK_INDEX =
(weight_RTV × z_RTV) +
(weight_Errors × z_Errors) +
(weight_Accuracy × z_AccuracyLoss) +
(weight_RT × z_RTMean) +
(weight_Drop × z_PerformanceDrop)
Step 4: Clinical Interpretation Bands
The ADHD Risk Index is interpreted using clinical bands that align with professional assessment standards:
| Risk Index | Interpretation | Risk Level |
|---|---|---|
| < 0.40 | No objective ADHD signal | Low Risk |
| 0.40 – 0.79 | Mild ADHD traits | Moderate Risk |
| 0.80 – 1.19 | Moderate ADHD-consistent signal | Moderate Risk |
| ≥ 1.20 | Strong ADHD-consistent signal | High Risk |
Step 5: Risk Percentage
The risk index is converted to a percentage (0-100) using the standard normal cumulative distribution function (CDF). This provides an intuitive "relative attention-regulation risk vs. norms" score that can be easily understood.
Example conversions:
- • Risk Index 0.5 → ~69% risk score
- • Risk Index 0.8 → ~79% risk score
- • Risk Index 1.0 → ~84% risk score
- • Risk Index 1.5 → ~93% risk score
Why This Methodology is Clinically Defensible
- ✓Matches CPT research consensus: Uses established findings from CPT research literature on ADHD markers
- ✓Standardization approach: Uses z-scores and weighting, not arbitrary raw score cutoffs
- ✓Focuses on regulation: Emphasizes attention regulation drift, not intelligence or overall cognitive ability
- ✓Aligned with professional tools: Similar approach to QBTest, Conners CPT, and TOVA composite scoring
- ✓Test-specific weights: Different weightings for Go/No-Go (inhibition) vs CPT-Lite (vigilance) reflect their distinct cognitive demands
Key Metrics Explained
Reaction Time Variability (RTV)
The standard deviation of reaction times across trials. High variability (inconsistent response times) is one of the strongest markers of ADHD, even when average reaction time is normal. This reflects fluctuations in attention and executive control.
Clinical significance: Research shows adults with ADHD have significantly higher RTV even with similar mean reaction times.
Omission Errors
Targets that were missed (failing to respond when you should). High omission errors indicate inattention—difficulty maintaining focus and detecting targets, a core ADHD symptom.
More important for CPT-Lite: Vigilance tasks are particularly sensitive to inattention.
Commission Errors
Incorrect responses (responding when you shouldn't). High commission errors indicate impulsivity—difficulty inhibiting responses, another core ADHD symptom.
More important for Go/No-Go: Inhibition tasks directly measure impulse control.
Accuracy
Overall correctness of responses. Normal performance is typically ~99% accuracy. Lower accuracy can indicate combined attention and impulse control challenges.
Speed-accuracy trade-off: Some individuals with ADHD show fast but inaccurate responses, while others show slow, cautious responses—both patterns are informative.
Performance Decrement
Decline in performance over time (measured as accuracy drop from first to last portion of the test). Large decrements suggest difficulty sustaining attention, a key ADHD indicator.
More relevant for CPT-Lite: Vigilance tasks measure sustained attention over longer periods.
Important Limitations
This is Supportive Evidence, Not Diagnostic
- Cognitive tests provide objective performance data but cannot diagnose ADHD alone
- Only a qualified healthcare professional can make an ADHD diagnosis
- Results may be influenced by factors other than ADHD (fatigue, stress, medication, other conditions)
- Performance can vary across sessions—one test result is not definitive
- Clinical norms are population-based averages; individual variation exists
- Our norms are conservative estimates; actual clinical assessments may use proprietary norms
Medical Disclaimer
- This cognitive assessment is for informational purposes only
- Not intended to replace professional medical evaluation, diagnosis, or treatment
- Results should be discussed with a qualified healthcare provider
- If you have concerns about ADHD, consult with a healthcare professional for comprehensive evaluation
- Emergency situations should be addressed immediately with appropriate medical care
Technical Notes
Normal CDF Approximation
We use the Abramowitz and Stegun approximation for the standard normal cumulative distribution function to convert risk indices to percentages. This is a standard statistical method used in clinical assessments.
Z-Score Clamping
Negative z-scores (performance better than normal) are clamped to 0. This ensures we only assess risk based on deviations that indicate potential challenges—no "penalty" for above-average performance.
References & Further Reading
Our methodology is based on established CPT research and aligns with how professional assessment tools work:
- Continuous Performance Test (CPT) research literature on ADHD markers
- Go/No-Go task research on response inhibition and ADHD
- QBTest, Conners CPT, and TOVA assessment methodologies
- Meta-analyses on reaction time variability as an ADHD marker
- Clinical norms from CPT validation studies
Specific clinical norms and weights are derived from research consensus and conservative estimates. Professional clinical assessments may use proprietary norms that are not publicly available.