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Research Terms Explained

Research Terms Explained

Plain-language definitions of the words that appear in study reports and news about autism research, drawn from NIH, ClinicalTrials.gov and NCCIH glossaries.

Based on ClinicalTrials.gov · NIH · NIH News in Health · NCCIH · MedlinePlus · NCI Dictionary and 1 more · All sources · Checked November 3, 2026

2 typesof clinical research: clinical trials (interventional) and observational studiesClinicalTrials.gov
20–80people in a typical Phase I trial; Phase III trials involve 1,000–3,000NIH
Placebolooks like the treatment and is given the same way, but contains no active drugClinicalTrials.gov

How studies are built

Clinical trial (interventional study)
A study in which researchers assign participants to get one or more interventions — a drug, a behavior program, a device — to test what happens. Participants usually do not choose their group. ClinicalTrials.gov describes two main types of clinical research: clinical trials and observational studies.
Observational study
A study in which researchers collect information from participants, or use data already collected, without assigning any intervention. It can find links, but cannot prove cause and effect.
Cohort
A group of people followed over time. NIH describes a cohort study as one that follows many people to learn how a condition arises and to find possible risk factors; NCI defines it as comparing an outcome in groups that are alike in many ways but differ by one characteristic.
Randomized controlled trial
A trial in which participants are assigned by chance (randomized) to a treatment group or a control group, to avoid bias in who gets which treatment. NIH calls a well-designed one the gold standard for showing that a treatment works. Often participants, researchers, or both are “masked” — not told which group a participant is in.
Control group
In a clinical trial, the group that does not receive the new treatment being studied; it is compared with the group that does, to see whether the treatment works.
Placebo
Something that looks like, and is given the same way as, the treatment being studied but contains no active drug. NIH notes placebos are not used when going without effective therapy would put you at risk, and you are told before joining if one is used.
Sample size
How many people take part (ClinicalTrials.gov calls this enrollment). MedlinePlus notes that larger studies generally give more reliable results and small studies usually need further confirmation.

Reading the numbers

Prevalence
The total number of people in a group who have (or had) a condition at a point in time or during a period of time.
Incidence
The number of new cases of a condition diagnosed each year.
Correlation vs. causation
An observational study can show that two things are linked (associated). Only a well-designed trial can show that one causes the other. NIH: observational studies “can’t prove cause and effect, but they can be useful for finding associations.”
Statistically significant
A mathematical measure of the difference between groups: the difference is greater than what would be expected by chance alone.
Clinically significant (effect size)
A measure of how large the effect is and how much it matters to patients. NCCIH notes a result can be statistically significant yet too small to be clinically useful.
Replication
Repeating a study with the same methods but different volunteers and investigators. It is how researchers learn whether results are reliable; a single study rarely gives a final answer.
Meta-analysis
A process that analyzes data from different studies on the same subject. Its results are usually stronger than those of any single study.

How results are shared and checked

Peer review
Experts in the field review a report before it is published in a scientific journal, to check that the analysis and conclusions are sound and the work meets current standards.
Preprint
A study posted on a preprint server for other scientists to weigh in on before it has been peer reviewed. NIH says such results should be treated with care and context because they have not yet been fully vetted.
Informed consent
The process of learning and discussing a study’s details — including risks and possible benefits — before deciding whether to take part. It continues throughout the study.
IRB (Institutional Review Board)
An independent committee of physicians, statisticians and community members that reviews and monitors research to protect participants’ rights and safety, before the study starts and as it proceeds.
Biomarker
A biological molecule found in blood, other body fluids or tissues that is a sign of a normal or abnormal process, or of a condition. It may also be used to see how the body responds to a treatment.
Organoid (laboratory model)
A three-dimensional, mini-organ-like structure grown in the laboratory from a person’s cells, such as stem cells. Organoids mimic some of the structure and functions of human tissue, but they are a laboratory model — not a person.
Definitions are paraphrased from the ClinicalTrials.gov glossary, the NIH glossary of common terms, NCCIH and the NCI Dictionary. Put them to work: how to read a study.

This website provides general educational information. It does not diagnose autism or replace individualized medical, developmental, psychological, or educational advice. Screening is not diagnosis.

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