ADHD or autism: what actually sets them apart
This page compares two ways of functioning that look alike from a distance and separate up close. It starts from ordinary situations rather than lists of criteria, because it is in a meeting, a last-minute change of plan or the day after a party that the difference becomes visible. It also states plainly what an online questionnaire will never do here: choose.
1What is the difference between ADHD and autism?
The difference lies less in visible behaviour than in what produces it. With an attention disorder, the difficulty is first about regulation: sustaining effort, holding a thread, delaying a reaction, returning to an interrupted task. On the autism spectrum, it is first about processing social and sensory information: reading what is implied, tolerating an environment, absorbing an unplanned change.
Two people can therefore leave the same meeting exhausted for opposite reasons. One fought to stay hooked to what was being said; the other followed easily but paid for the noise, the lighting and the turn-taking. The table below applies that logic to six ordinary situations.
| Situation | What comes up on the attention side | What comes up on the autism side |
|---|---|---|
| A meeting that drags on | The thread is lost, attention drifts off, you come back not knowing where things stand | The thread is easy to follow, but noise, lighting and turn-taking are costly |
| A plan changed the night before | Often taken well, sometimes even a relief | Costly: the whole sequence has to be rebuilt, and irritation can rise |
| A noisy workspace | Impossible to stay on one task, everything passing by grabs attention | The noise becomes physically unpleasant, the priority is getting out of it |
| A group conversation | You cut in, answer too fast, forget what the other person just said | You decode what is implied more slowly, and prepare answers in advance |
| The day after a social evening | Tiredness from the effort of paying attention and from oversights to catch up on | Tiredness from social decoding and from the environment, sometimes lasting days |
| Daily routines | Hard to set up, harder still to keep going over time | Often set up deliberately, because they save energy |
2Why are the two so often confused?
First because the observable difficulties look alike. Antshel and Russo, in a 2019 review, describe shared genetic heritability and common difficulties in social functioning and executive functioning, while concluding that the differences remain large enough to keep two distinct categories. Put differently: what shows overlaps, what produces the behaviour rather less.
Then because attention is not a single function. Hours and colleagues, in 2022, note that several executive difficulties associated with attention disorders are also found in autistic people, and that selective attention does not behave the same way in the two configurations. A questionnaire that simply asks whether you find it hard to concentrate cannot separate them.
Finally because the classifications themselves kept the confusion alive for a long time. Until 2013, the two categories were mutually exclusive: recognising one meant ruling out the other. Adults now over forty were therefore assessed under a regime in which coexistence was simply not provided for.
- Social camouflage blurs both pictures, particularly in women: the effort of compensating reads as tiredness rather than as difficulty.
- Anxiety frequently settles on top of either one and redistributes the visible symptoms.
- Lasting lack of sleep degrades everyone's attention, and says nothing about neurodevelopment.
3Can someone be concerned by both at once?
Yes, and it is common. The meta-analysis by Rong and colleagues, published in 2021 and covering 63 studies, puts at 38.5% the proportion of autistic people affected at the time of the study by an attention disorder, and at 40.2% across the lifespan. The systematic review by Lai and colleagues, published in 2019 in The Lancet Psychiatry and based on 96 studies, reports a lower estimate of 28%.
| Publication | Number of studies | Pooled estimate |
|---|---|---|
| Rong et al., 2021 | 63 | 38.5% at the time of the study, 40.2% across the lifespan |
| Lai et al., 2019 | 96 | 28% (95% confidence interval: 25 to 32) |
The gap between those two figures is not a contradiction, it is information. Estimates vary with how participants are recruited, with age, with the presence of intellectual disability and with the criteria used. Hours and colleagues note that rates reported in the literature span a very wide range. Remembering roughly one third is more honest than one number presented as settled.
The practical consequence is simple: the question of which one is often the wrong question. For a substantial share of the people concerned, the answer is both, to differing degrees, and it is that combination that best explains what they live through.
4What each questionnaire looks at, and what it ignores
A questionnaire sees only what it asks. The two Brain Quiz questionnaires involved here have 28 items each and are read across four axes, but those axes do not overlap. Knowing what each one leaves out is worth more than comparing two scores out of 100 that do not measure the same thing.
| Questionnaire | What it looks at | What it does not look at |
|---|---|---|
| ADHD in adults, 28 items | Sustained attention, organisation and planning, restlessness and impulsivity, emotional regulation | Sensory processing, reading what is implied, the need for stable landmarks |
| Adult autism spectrum, 28 items | Social interaction, communication, routines and flexibility, sensory processing | Sustained attention, forgetfulness, impulsivity, planning |
Both share the same arithmetic: each answer is worth 0 to 4 points, multiplied by a weight between 1 and 3, the total is rescaled to 100 and placed in one of four reading bands. Those weights and thresholds were set by the editorial team. They come from no calibration on a population, so neither score compares to a norm.
5What should you do if both descriptions speak to you?
- Write down five concrete, dated situations, specifying what was costly: staying hooked, or tolerating the environment. That distinction interests a professional far more than a score does.
- Look for what already existed in primary school. How far back the difficulties go is the first thing sought in both cases, and it is documented with memories, school reports, the view of someone close.
- Watch what happens when the pressure lifts: a weekend with no obligations, a holiday. A difficulty that disappears entirely at rest points somewhere different from one that stays put.
- Talk to your family doctor with those examples in hand. They are the ones who refer you to the right professional or service, and waiting times are often long, so starting early saves months.
- Do not decide in their place. Arriving with the idea that it must be one or the other closes the discussion; arriving with situations opens it.
What this guide does not say
This page describes what the two profiles share and what separates them in ordinary situations. It does not cover the criteria professionals use, assessment pathways or possible support, and it replaces no medical advice. The figures quoted come from the publications listed in the sources and concern the samples described there, not your own situation. The two questionnaires linked from this page are self-observation questionnaires: they can neither confirm nor rule out a disorder, and they are not a way to choose between the two.
Frequently asked questions
- Can someone have ADHD and be autistic at the same time?
- Yes. Since 2013, the reference manual of the American Psychiatric Association recognises both in the same person, which earlier editions forbade. Published estimates vary with method: 38.5% in a 2021 meta-analysis covering 63 studies, 28% in a 2019 systematic review covering 96 studies. Remembering roughly one third stays more cautious than any single figure.
- Can an online questionnaire tell me which of the two applies to me?
- No, and none should claim to. A questionnaire measures how you describe your functioning at one moment. It does not reconstruct your history since childhood, does not look for what best explains your difficulties, and cannot separate lasting lack of sleep from a neurodevelopmental pattern. Only an assessment carried out by a health professional does that work.
- Which of the two questionnaires should I start with?
- The one whose description speaks to you most, without treating it as a commitment. Both have 28 items and take about eight minutes, and you can answer both. The most useful result is not the higher score but the breakdown by axis: it tells you which registers your answers cluster on, and that is what can be recounted in an appointment.
- Why were the two long considered incompatible?
- Because earlier classifications made them mutually exclusive: recognising one meant ruling out the other. Hours and colleagues restate this point in 2022. The consequence is still visible today among adults assessed before 2013, for whom coexistence was not envisaged, and among those who grew up with only one of the two explanations.
Sources
- Rong, Y., Yang, C.-J., Jin, Y., & Wang, Y. (2021). Prevalence of attention-deficit/hyperactivity disorder in individuals with autism spectrum disorder: A meta-analysis. Research in Autism Spectrum Disorders, 83, 101759. DOI 10.1016/j.rasd.2021.101759 (opens in a new tab)Méta-analyse de 63 études. Prévalence actuelle regroupée de 38,5 % (IC à 95 % : 34,0 à 43,2), prévalence sur la vie entière de 40,2 % (IC à 95 % : 34,9 à 45,7).
- Lai, M.-C., Kassee, C., Besney, R., Bonato, S., Hull, L., Mandy, W., Szatmari, P., & Ameis, S. H. (2019). Prevalence of co-occurring mental health diagnoses in the autism population: a systematic review and meta-analysis. The Lancet Psychiatry, 6(10), 819-829. DOI 10.1016/S2215-0366(19)30289-5 (opens in a new tab)Revue systématique de 96 études. Estimation regroupée de 28 % (IC à 95 % : 25 à 32) pour le trouble de l'attention dans la population autiste.
- Hours, C., Recasens, C., & Baleyte, J.-M. (2022). ASD and ADHD Comorbidity: What Are We Talking About?. Frontiers in Psychiatry, 13, 837424. DOI 10.3389/fpsyt.2022.837424 (opens in a new tab)Revue en accès libre. Rappelle que les classifications antérieures rendaient les deux catégories mutuellement exclusives, et détaille les recouvrements sur l'attention et les fonctions exécutives.
- Antshel, K. M., & Russo, N. (2019). Autism Spectrum Disorders and ADHD: Overlapping Phenomenology, Diagnostic Issues, and Treatment Considerations. Current Psychiatry Reports, 21(5), 34. DOI 10.1007/s11920-019-1020-5 (opens in a new tab)Synthèse : héritabilité génétique partagée et difficultés communes sur le fonctionnement social et exécutif, mais différences suffisantes pour maintenir deux catégories distinctes.
Related questionnaires
These questionnaires cover the subject of this guide. Each one states where its statements come from and how it is scored.
ADHD test for adults
Free online ADHD test for adults, no sign-up: 28 items, 4 reading axes, an immediate result, with the method and the sources published.
Autism test for adults
Free online autism test for adults, no sign-up: 28 concrete situations, 4 reading axes, an immediate result and a public methodology page.