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    1. Verbal Fluency TestGradeA
    2. Stroop Color-Word TestGradeA
    3. Trail Making TestGradeA
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    6. Digit Span TestGradeA
    7. Symbol Coding TestGradeA
    8. Verbal Learning TestGradeA
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    • Older Adult Executive SpeedGradeA20 min
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    • Motor and AttentionGradeA−29 min
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    Registered studies

    • Dementia and Alzheimer's1,673
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    All 25 conditions
    16,361Registered studies name a cognitive test in an outcome measure11,688 name a test you can run hereExplore the studies
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  2. /Data
  3. /Clinical trials
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  5. /COVID-19 and long COVID

Clinical trials data

Cognitive tests in COVID-19 and long COVID trials: 221 registered studies

Every registered COVID-19 and long COVID study on ClinicalTrials.gov that names a cognitive test in an outcome measure: the tests used most, how often as a primary outcome, which tests go together, how large the studies are and when they measure the outcome.

Registered COVID-19 and long COVID studies name a cognitive test in an outcome
221
Name one in a primary outcome
71
See the tests
Median participants per study
89
By phase
Led by industry
13

The tests COVID-19 and long COVID trials use most

The Trail Making Test leads: 36 of the 221 studies name it, 16%. Next comes the Digit Span Test (31). As a primary outcome, the Trail Making Test leads with 15 studies.

  1. 1

    Trail Making Test36 studies, 15 as a primary outcome

  2. 2

    Digit Span Test31 studies, 14 as a primary outcome

  3. 3

    Stroop Color-Word Test30 studies, 13 as a primary outcome

  4. 4

    Verbal Fluency24 studies, 8 as a primary outcome

  5. 5

    Verbal Learning22 studies, 8 as a primary outcome

  6. 6

    Symbol Coding21 studies, 5 as a primary outcome

  7. 7

    Category Fluency14 studies, 5 as a primary outcome

  8. 8

    Continuous Performance Test9 studies, 2 as a primary outcome

  9. 9

    Complex Figure Copy and Recall8 studies, 4 as a primary outcome

  10. 10

    Simple Reaction Time7 studies, 2 as a primary outcome

  11. 11

    Picture Naming Test6 studies, 4 as a primary outcome

  12. 12

    Tower Planning6 studies, 1 as a primary outcome

  13. 13

    Short Story Recall4 studies, 3 as a primary outcome

  14. 14

    N-Back Task4 studies, 2 as a primary outcome

  15. 15

    Paired Associate Learning4 studies, 1 as a primary outcome

  16. 16

    Rapid Visual Information Processing4 studies, 1 as a primary outcome

  17. 17

    Task Switching Test4 studies, 1 as a primary outcome

  18. 18

    Matrix Reasoning3 studies, 2 as a primary outcome

  19. 19

    Psychomotor Vigilance Task3 studies, 2 as a primary outcome

  20. 20

    Size Order Memory Test3 studies, 2 as a primary outcome

  21. 21

    Clock Drawing Task3 studies, 1 as a primary outcome

  22. 22

    Effort Discounting Task3 studies, 1 as a primary outcome

  23. 23

    Choice Reaction Time3 studies, 0 as a primary outcome

  24. 24

    Recognition Memory Test3 studies, 0 as a primary outcome

  25. 25

    Word Pair Learning2 studies, 2 as a primary outcome

A test as a primary outcomeOnly in secondary or other outcomes

50% of COVID-19 and long COVID studies name only instruments outside the library, such as clinician-administered screening scales. They count in every figure on this page and are not listed. The explorer below holds all 58 tests.

Tests used together

The pairs of tests COVID-19 and long COVID studies name together most often.
  1. Stroop Color-Word Test and Trail Making Test18 studies name both
  2. Digit Span Test and Trail Making Test17 studies name both
  3. Trail Making Test and Verbal Learning13 studies name both
  4. Digit Span Test and Stroop Color-Word Test12 studies name both
  5. Digit Span Test and Verbal Learning12 studies name both
  6. Stroop Color-Word Test and Verbal Fluency11 studies name both
  7. Digit Span Test and Verbal Fluency10 studies name both
  8. Stroop Color-Word Test and Verbal Learning10 studies name both
  9. Trail Making Test and Verbal Fluency10 studies name both
  10. Category Fluency and Digit Span Test9 studies name both

Studies by start year

Each study counted once. 2026 is partly planned starts.
02000: 0 studies, 0 with a test as a primary outcome20002001: 0 studies, 0 with a test as a primary outcome2002: 0 studies, 0 with a test as a primary outcome2003: 0 studies, 0 with a test as a primary outcome2004: 0 studies, 0 with a test as a primary outcome2005: 0 studies, 0 with a test as a primary outcome20052006: 0 studies, 0 with a test as a primary outcome2007: 0 studies, 0 with a test as a primary outcome2008: 0 studies, 0 with a test as a primary outcome2009: 0 studies, 0 with a test as a primary outcome2010: 0 studies, 0 with a test as a primary outcome20102011: 0 studies, 0 with a test as a primary outcome2012: 0 studies, 0 with a test as a primary outcome2013: 0 studies, 0 with a test as a primary outcome2014: 0 studies, 0 with a test as a primary outcome2015: 0 studies, 0 with a test as a primary outcome20152016: 0 studies, 0 with a test as a primary outcome2017: 0 studies, 0 with a test as a primary outcome2018: 2 studies, 0 with a test as a primary outcome2019: 0 studies, 0 with a test as a primary outcome2020: 41 studies, 16 with a test as a primary outcome20202021: 46 studies, 16 with a test as a primary outcome2022: 31 studies, 12 with a test as a primary outcome2023: 52 studies, 12 with a test as a primary outcome2024: 20 studies, 3 with a test as a primary outcome2025: 18 studies, 6 with a test as a primary outcome20252026: 11 studies, 6 with a test as a primary outcome

A test as a primary outcomeOnly in secondary or other outcomes

Show as a table
Registered studies by start year
Start yearStudiesA test as a primary outcome
200000
200100
200200
200300
200400
200500
200600
200700
200800
200900
201000
201100
201200
201300
201400
201500
201600
201700
201820
201900
20204116
20214616
20223112
20235212
2024203
2025186
2026116

Phases and sponsors

By phase

  • Early phase 12 studies, 0 as a primary outcome
  • Phase 13 studies, 1 as a primary outcome
  • Phase 1/23 studies, 2 as a primary outcome
  • Phase 225 studies, 4 as a primary outcome
  • Phase 2/34 studies, 0 as a primary outcome
  • Phase 35 studies, 1 as a primary outcome
  • Phase 44 studies, 1 as a primary outcome
  • Not applicable97 studies, 29 as a primary outcome
  • Observational78 studies, 33 as a primary outcome

Sponsors and study types

Lead sponsor: industry 13, NIH 1, universities, hospitals and others 207. Interventional 143, observational 78.

Status, results, interventions and countries

Status

  • Recruiting34 studies, 11 as a primary outcome
  • Not yet recruiting8 studies, 2 as a primary outcome
  • Active, not recruiting15 studies, 2 as a primary outcome
  • Completed110 studies, 33 as a primary outcome
  • Stopped early13 studies, 3 as a primary outcome
  • Status unknown41 studies, 20 as a primary outcome

What they test

  • Behavioral43 studies, 12 as a primary outcome
  • Drug39 studies, 10 as a primary outcome
  • Device37 studies, 16 as a primary outcome
  • Dietary supplement10 studies, 3 as a primary outcome
  • Procedure8 studies, 1 as a primary outcome
  • Diagnostic test7 studies, 3 as a primary outcome
  • Biological8 studies, 4 as a primary outcome
  • Combination product1 studies, 0 as a primary outcome
  • Genetic1 studies, 0 as a primary outcome
  • Other63 studies, 13 as a primary outcome
  • None given32 studies, 16 as a primary outcome

Intervention types as registered. A study can list several; observational studies often list none.

Where their sites are

  • United States61 studies, 16 as a primary outcome
  • Germany16 studies, 3 as a primary outcome
  • Spain16 studies, 5 as a primary outcome
  • Canada12 studies, 4 as a primary outcome
  • France12 studies, 2 as a primary outcome
  • United Kingdom11 studies, 2 as a primary outcome
  • Italy8 studies, 3 as a primary outcome
  • Sweden7 studies, 3 as a primary outcome
  • Türkiye7 studies, 4 as a primary outcome
  • Chile6 studies, 1 as a primary outcome
  • China6 studies, 3 as a primary outcome
  • Switzerland6 studies, 2 as a primary outcome

36 countries in all. A study with sites in several counts in each; 8 list no site.

Reported results

Completed studies with results posted on ClinicalTrials.gov, a results paper the registry links to the study, or both.

Completed COVID-19 and long COVID studies: 40 of 110, 36%

Every completed study with a cognitive outcome: 3,626 of 7,953, 46%

Completed COVID-19 and long COVID studies and every completed study, by how they reported results
ResultsCompleted COVID-19 and long COVID studiesEvery completed study
Results on ClinicalTrials.gov and a paper8, 7%776, 10%
Results on ClinicalTrials.gov only6, 5%1,139, 14%
A results paper only26, 24%1,711, 22%
Neither70, 64%4,327, 54%

How many participants they enroll

Enrollment as registered: actual for a finished study, planned for one still recruiting.
102050100200500
  • Phase 288 median, 40 to 142
  • Not applicable60 median, 38 to 104
  • Observational194 median, 65 to 400
Participants per study. The bar spans the middle half of the studies in each phase, the mark is the median, and the axis is logarithmic. Phases with fewer than 10 studies that give a size are left out.
Show as a table
Participants per COVID-19 and long COVID study by phase
PhaseStudies with a sizeMedianMiddle half
Phase 2248840 to 142
Not applicable966038 to 104
Observational7719465 to 400

When the cognitive outcome is measured

Half of the primary outcomes that name a library test are measured within 12 weeks of the start, and the middle half from 7 weeks to 9 months. 110 primary outcomes give a duration.

Latest time point of each outcome

  • Within a day22 outcomes, 8 as a primary outcome
  • Up to 4 weeks35 outcomes, 14 as a primary outcome
  • 1 to 3 months125 outcomes, 39 as a primary outcome
  • 3 to 6 months49 outcomes, 19 as a primary outcome
  • 6 to 12 months47 outcomes, 30 as a primary outcome
  • 1 to 2 years2 outcomes, 0 as a primary outcome
  • Over 2 years8 outcomes, 0 as a primary outcome
  • No duration given6 outcomes, 1 as a primary outcome

A test as a primary outcomeOnly in secondary or other outcomes

288 of the 294 outcome measures give a duration. A single visit counts as within a day.

Median time to the primary outcome, by test

Median weeks to the latest time point of each test's primary outcomes
TestPrimary outcomesMedian
Trail Making Test1513 weeks
Digit Span Test144 months
Stroop Color-Word Test1313 weeks

Explore the COVID-19 and long COVID studies

The 111 COVID-19 and long COVID studies that name a test in the library, with filters for test, phase, sponsor, status, country, intervention, outcome list, size and start year. Each study links to its record on ClinicalTrials.gov.
ConditionCOVID-19 and long COVID

111 studies match. 40 name a library test in a primary outcome. Median size 84 participants. Median time to the primary outcome: 12 weeks.

Loading 111 studies; the filters turn on when they arrive.

By start year
01020302000: 0 studies, 0 naming a library test in a primary outcome20002001: 0 studies, 0 naming a library test in a primary outcome2002: 0 studies, 0 naming a library test in a primary outcome2003: 0 studies, 0 naming a library test in a primary outcome2004: 0 studies, 0 naming a library test in a primary outcome2005: 0 studies, 0 naming a library test in a primary outcome20052006: 0 studies, 0 naming a library test in a primary outcome2007: 0 studies, 0 naming a library test in a primary outcome2008: 0 studies, 0 naming a library test in a primary outcome2009: 0 studies, 0 naming a library test in a primary outcome2010: 0 studies, 0 naming a library test in a primary outcome20102011: 0 studies, 0 naming a library test in a primary outcome2012: 0 studies, 0 naming a library test in a primary outcome2013: 0 studies, 0 naming a library test in a primary outcome2014: 0 studies, 0 naming a library test in a primary outcome2015: 0 studies, 0 naming a library test in a primary outcome20152016: 0 studies, 0 naming a library test in a primary outcome2017: 0 studies, 0 naming a library test in a primary outcome2018: 1 studies, 0 naming a library test in a primary outcome2019: 0 studies, 0 naming a library test in a primary outcome2020: 9 studies, 5 naming a library test in a primary outcome20202021: 26 studies, 10 naming a library test in a primary outcome2022: 15 studies, 7 naming a library test in a primary outcome2023: 28 studies, 6 naming a library test in a primary outcome2024: 15 studies, 1 naming a library test in a primary outcome2025: 9 studies, 5 naming a library test in a primary outcome20252026: 8 studies, 6 naming a library test in a primary outcome

2026 is partly planned starts.

Show as a table
Matching studies by start year
Start yearStudiesAs a primary outcome
200000
200100
200200
200300
200400
200500
200600
200700
200800
200900
201000
201100
201200
201300
201400
201500
201600
201700
201810
201900
202095
20212610
2022157
2023286
2024151
202595
202686

Library tests named most

Largest condition groups

  • COVID-19 and long COVID111 studies, 40 as a primary outcome
  • Pain and fatigue32 studies, 12 as a primary outcome
  • Depression and bipolar disorder8 studies, 4 as a primary outcome
  • Anxiety, PTSD and OCD8 studies, 3 as a primary outcome
  • Mild cognitive impairment4 studies, 1 as a primary outcome
  • Sleep and sleep disorders3 studies, 1 as a primary outcome
  • Brain injury and concussion2 studies, 0 as a primary outcome
  • Multiple sclerosis2 studies, 1 as a primary outcome
  • Healthy volunteers2 studies, 1 as a primary outcome
  • Delirium, surgery and intensive care2 studies, 1 as a primary outcome
  • Parkinson's disease1 study, 0 as a primary outcome
  • ADHD1 study, 1 as a primary outcome

Phases

Participants

Lead sponsor: industry 5, other 106. Interventional 82, observational 29.

As a primary outcomeSecondary or other outcome

The studies, newest registration first

Each number opens the study's record on ClinicalTrials.gov.

Registered studies that match the filters, newest registration first, with the library tests each one names and the outcome list that names them.
StudyStartPhaseConditionsParticipantsLead sponsorStatusLibrary tests named, with the latest time point
NCT07881029Start2026PhaseObservationalConditionsCOVID-19 and long COVIDParticipants55Lead sponsorOtherStatusCompletedLibrary tests named
  • Trail Making TestPrimary6 months
  • Stroop Color-Word TestPrimary6 months
NCT07783074Start2026PhaseObservationalConditionsMultiple sclerosis, Healthy volunteers, COVID-19 and long COVID, Pain and fatigueParticipants122Lead sponsorOtherStatusRecruitingLibrary tests named
  • Symbol CodingSecondary9 weeks
  • Finger Tapping TaskPrimary9 weeks
NCT07724834Start2026PhasePhase 2ConditionsCOVID-19 and long COVID, Pain and fatigueParticipants38Lead sponsorOtherStatusNot yet recruitingLibrary tests named
  • Symbol CodingSecondary9 months
NCT07709234Start2026PhaseNot applicableConditionsCOVID-19 and long COVID, Pain and fatigueParticipants20Lead sponsorOtherStatusNot yet recruitingLibrary tests named
  • Stroop Color-Word TestPrimary3 days
  • Verbal FluencyPrimary3 days
NCT07429903Start2023PhaseNot applicableConditionsCOVID-19 and long COVID, Pain and fatigueParticipants31Lead sponsorOtherStatusCompletedLibrary tests named
  • Trail Making TestSecondary12 weeks
  • Symbol Scan TaskSecondary12 weeks
NCT07359482Start2026PhasePhase 3ConditionsCOVID-19 and long COVID, Pain and fatigueParticipants160Lead sponsorOtherStatusRecruitingLibrary tests named
  • N-Back TaskSecondary12 weeks
NCT07355751Start2026PhaseNot applicableConditionsCOVID-19 and long COVIDParticipants108Lead sponsorOtherStatusNot yet recruitingLibrary tests named
  • Trail Making TestSecondary8 weeks
  • Stroop Color-Word TestSecondary8 weeks
  • Verbal LearningSecondary8 weeks
  • Verbal FluencyPrimary8 weeks
  • Digit Span TestSecondary8 weeks
  • Category FluencySecondary8 weeks
  • Picture Naming TestSecondary8 weeks
  • Complex Figure Copy and RecallSecondary8 weeks
NCT07278388Start2025PhaseNot applicableConditionsCOVID-19 and long COVID, Pain and fatigueParticipants200Lead sponsorOtherStatusRecruitingLibrary tests named
  • Effort Discounting TaskPrimary
NCT07278206Start2025PhaseNot applicableConditionsCOVID-19 and long COVIDParticipants66Lead sponsorOtherStatusRecruitingLibrary tests named
  • Trail Making TestSecondary6 months
  • Stroop Color-Word TestSecondary6 months
  • Tower PlanningSecondary2 weeks
  • Simple Reaction TimeSecondary6 months
  • Effort Discounting TaskSecondary2 weeks
NCT07051967Start2025PhaseObservationalConditionsCOVID-19 and long COVIDParticipants40Lead sponsorOtherStatusRecruitingLibrary tests named
  • Category FluencySecondary
  • Clock Drawing TaskSecondary
NCT07021794Start2025PhasePhase 2ConditionsCOVID-19 and long COVIDParticipants100Lead sponsorOtherStatusRecruitingLibrary tests named
  • Simple Reaction TimeSecondary6 months
NCT07005921Start2025PhaseNot applicableConditionsCOVID-19 and long COVID, Pain and fatigueParticipants40Lead sponsorOtherStatusCompletedLibrary tests named
  • Digit Span TestPrimary5 weeks
NCT06932237Start2025PhaseObservationalConditionsCOVID-19 and long COVIDParticipants200Lead sponsorOtherStatusRecruitingLibrary tests named
  • Verbal FluencyPrimary12 months
  • Tower PlanningPrimary12 months
  • Paired Associate LearningPrimary12 months
  • Rapid Visual Information ProcessingPrimary12 months
NCT06928506Start2025PhaseNot applicableConditionsCOVID-19 and long COVIDParticipants120Lead sponsorOtherStatusRecruitingLibrary tests named
  • Simple Reaction TimePrimary9 weeks
  • Word Pair LearningPrimary9 weeks
NCT06897553Start2024PhaseNot applicableConditionsBrain injury and concussion, Depression and bipolar disorder, COVID-19 and long COVID, Anxiety, PTSD and OCDParticipants44Lead sponsorOtherStatusRecruitingLibrary tests named
  • Stroop Color-Word TestSecondary8 weeks
  • Verbal FluencySecondary8 weeks
NCT06895850Start2021PhaseNot applicableConditionsCOVID-19 and long COVIDParticipants20Lead sponsorOtherStatusCompleted

Paper

Library tests named
  • Category FluencySecondary8 weeks
NCT06850350Start2026PhaseObservationalConditionsCOVID-19 and long COVIDParticipants136Lead sponsorOtherStatusRecruitingLibrary tests named
  • Size Order Memory TestPrimarysame day
NCT06614309Start2024PhaseNot applicableConditionsCOVID-19 and long COVID, Pain and fatigueParticipants45Lead sponsorOtherStatusRecruitingLibrary tests named
  • Trail Making TestSecondary2 weeks
  • Verbal LearningSecondary2 weeks
  • Task Switching TestSecondary2 weeks
NCT06586398Start2025PhaseNot applicableConditionsCOVID-19 and long COVID, Pain and fatigueParticipants10Lead sponsorOtherStatusCompletedLibrary tests named
  • Verbal FluencySecondary12 weeks
  • Short Story RecallSecondary12 weeks
NCT06510985Start2024PhaseNot applicableConditionsCOVID-19 and long COVID, Pain and fatigueParticipants120Lead sponsorOtherStatusActive, not recruitingLibrary tests named
  • Effort Discounting TaskSecondary6 weeks
NCT06503874Start2024PhaseNot applicableConditionsCOVID-19 and long COVID, Pain and fatigueParticipants58Lead sponsorOtherStatusCompletedLibrary tests named
  • Digit Span TestOther outcome2 years
  • Continuous Performance TestSecondary2 years
NCT06476496Start2024PhaseNot applicableConditionsCOVID-19 and long COVID, Pain and fatigueParticipants93Lead sponsorOtherStatusCompleted

Results

Library tests named
  • Verbal FluencySecondary5 months
NCT06452095Start2026PhaseNot applicableConditionsCOVID-19 and long COVIDParticipants120Lead sponsorOtherStatusRecruitingLibrary tests named
  • Digit Span TestSecondary6 months
  • Continuous Performance TestSecondary6 months
  • Choice Reaction TimeSecondary6 months
  • Simple Reaction TimePrimary9 weeks
  • AX Continuous Performance TestWording unclear
  • Word Pair LearningPrimary9 weeks
  • Gradual-Onset Continuous Performance TaskSecondary6 months
NCT06391489Start2024PhaseNot applicableConditionsCOVID-19 and long COVIDParticipants10Lead sponsorOtherStatusActive, not recruitingLibrary tests named
  • Verbal LearningSecondary9 weeks
  • Symbol CodingSecondary9 weeks
NCT06366724Start2024PhasePhase 2ConditionsCOVID-19 and long COVID, Pain and fatigueParticipants160Lead sponsorOtherStatusRecruitingLibrary tests named
  • Simple Reaction TimeSecondary15 weeks

Page 1 of 5

Questions, answered from the data

Which cognitive test do COVID-19 and long COVID trials use most?

The Trail Making Test: 36 of the 221 registered studies name it in an outcome measure, 16%. Next come the Digit Span Test (31) and the Stroop Color-Word Test (30).

Which cognitive test do COVID-19 and long COVID trials use most as a primary outcome?

The Trail Making Test, named in a primary outcome by 15 studies. 71 of the 221 studies, 32%, name a cognitive test in a primary outcome.

How many participants does a phase 2 COVID-19 and long COVID trial enroll?

Half of the phase 2 COVID-19 and long COVID studies enroll 88 participants or fewer, and the middle half enroll 40 to 142. 24 of them give a size.

How long after the start do COVID-19 and long COVID trials measure a cognitive outcome?

Half of the primary outcomes that name a library test are measured within 12 weeks of the start, and the middle half from 7 weeks to 9 months. 110 primary outcomes give a duration.

Which cognitive tests do COVID-19 and long COVID trials use together?

The Stroop Color-Word Test with the Trail Making Test most often: 18 studies name both. Next, the Digit Span Test with the Trail Making Test (17).

How many completed COVID-19 and long COVID trials have reported results?

40 of the 110 completed COVID-19 and long COVID studies, 36%, have reported results: 14 posted them on ClinicalTrials.gov, 34 have a results paper linked to the registry record, and 8 did both. The other 70 show neither. Of all completed studies with a cognitive outcome, 46% have reported results.

Other conditions

  • Pain and fatigue46 shared
  • Depression and bipolar disorder15 shared
  • Anxiety, PTSD and OCD15 shared
  • Delirium, surgery and intensive care14 shared
  • Mild cognitive impairment7 shared
  • Stroke6 shared
  • Lung disease5 shared
  • Parkinson's disease4 shared
  • Multiple sclerosis4 shared
  • Brain injury and concussion4 shared
  • Dementia and Alzheimer's3 shared
  • Aging, frailty and exercise3 shared
  • Sleep and sleep disorders3 shared
  • Cardiovascular disease3 shared
  • Healthy volunteers2 shared
  • Obesity and diabetes2 shared
  • Substance use and addiction1 shared
  • Cancer1 shared
  • ADHD1 shared
  • Epilepsy1 shared
  • Schizophrenia and psychosis640 studies
  • Cognitive impairment and decline354 studies
  • Hearing loss247 studies
  • Autism200 studies

All 16,361 registered studies, by test, condition, phase and year.

How the studies are counted

For each test family, the census runs ClinicalTrials.gov's own outcome search for the family's names and reads every study first posted by the day the family was counted. These studies were read on 10 November 2026. A study counts once on a page, however many tests it names. Counts for a test cover every version of the task under any of its names, so a page can count studies that used a commercial version.

The census adds two things to each record and changes nothing in it: which outcome list names the test (primary, then secondary, then other), and the condition groups, matched on the study's condition names and MeSH terms. A study can fall in several groups; one whose only condition is cognitive impairment or decline falls in “Cognitive impairment and decline”. Studies that name only instruments outside the library count in every total and share but are not listed.

A second read on 10 November 2026 added each study's overall status, whether results are posted, its intervention types, the countries of its sites and the time frame of the outcome that names each test. A time frame counts by the latest time point it names: “Baseline, 12 and 24 weeks” is 24 weeks, a single visit is within a day, and one that names no duration, such as “end of treatment”, is left out of the timings.

A third read on 10 November 2026 added the papers the registry links to each study: those its sponsor lists as reporting results, and those PubMed links to it through the study's NCT number. A study has a results paper when one of them came out in or after the month of its primary completion and PubMed does not class it as a protocol, review or comment. A paper that never gives the NCT number is not linked, so some studies counted as reporting neither did publish.

Source: ClinicalTrials.gov, a database of the U.S. National Library of Medicine, which does not endorse these pages. Every study line is in the data release 2.1.0, and the explorer's own file is clinical-trials-studies.json.

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