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    1. Verbal Fluency TestGradeA
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    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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  1. Home
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  3. /Clinical trials
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  5. /Parkinson's disease
  6. /Verbal Fluency

Clinical trials data

Verbal Fluency in Parkinson's disease trials: 140 registered studies

Every registered Parkinson's disease study on ClinicalTrials.gov that names Verbal Fluency in an outcome measure: how often it is a primary outcome, the tests named with it, how large the studies are and when they measure it.

Registered Parkinson's disease studies name it in an outcome measure
140
Name it in a primary outcome, 32%
45 of 140
Of the condition's 892 studies name it, against 11% of all registered studies
16%
Other conditions
Median participants per study
44
By phase
Try Verbal Fluency

Tests named in the same studies

The library tests that Parkinson's disease studies naming Verbal Fluency name most often beside it.
  1. 1

    Trail Making Test50 studies, 10 as a primary outcome

  2. 2

    Digit Span Test43 studies, 6 as a primary outcome

  3. 3

    Stroop Color-Word Test42 studies, 11 as a primary outcome

  4. 4

    Verbal Learning33 studies, 11 as a primary outcome

  5. 5

    Category Fluency29 studies, 10 as a primary outcome

  6. 6

    Picture Naming Test25 studies, 2 as a primary outcome

  7. 7

    Clock Drawing Task18 studies, 3 as a primary outcome

  8. 8

    Symbol Coding17 studies, 4 as a primary outcome

  9. 9

    Line Angle Matching15 studies, 3 as a primary outcome

  10. 10

    Card Sorting Test (Berg)13 studies, 4 as a primary outcome

A test as a primary outcomeOnly in secondary or other outcomes

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: 1 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: 1 studies, 0 with a test as a primary outcome20102011: 3 studies, 1 with a test as a primary outcome2012: 4 studies, 1 with a test as a primary outcome2013: 4 studies, 0 with a test as a primary outcome2014: 6 studies, 2 with a test as a primary outcome2015: 2 studies, 0 with a test as a primary outcome20152016: 7 studies, 1 with a test as a primary outcome2017: 12 studies, 2 with a test as a primary outcome2018: 12 studies, 2 with a test as a primary outcome2019: 10 studies, 6 with a test as a primary outcome2020: 12 studies, 5 with a test as a primary outcome20202021: 14 studies, 5 with a test as a primary outcome2022: 12 studies, 2 with a test as a primary outcome2023: 10 studies, 6 with a test as a primary outcome2024: 9 studies, 4 with a test as a primary outcome2025: 10 studies, 4 with a test as a primary outcome20252026: 11 studies, 4 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
200410
200500
200600
200700
200800
200900
201010
201131
201241
201340
201462
201520
201671
2017122
2018122
2019106
2020125
2021145
2022122
2023106
202494
2025104
2026114

Phases and study sizes

By phase

  • Early phase 13 studies, 0 as a primary outcome
  • Phase 14 studies, 0 as a primary outcome
  • Phase 1/22 studies, 2 as a primary outcome
  • Phase 214 studies, 2 as a primary outcome
  • Phase 32 studies, 0 as a primary outcome
  • Phase 43 studies, 1 as a primary outcome
  • Not applicable87 studies, 26 as a primary outcome
  • Observational25 studies, 14 as a primary outcome

Participants per study

102050100200
  • Phase 267 median, 31 to 117
  • Not applicable34 median, 21 to 65
  • Observational100 median, 52 to 163
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 Parkinson's disease study that names Verbal Fluency, by phase
PhaseStudies with a sizeMedianMiddle half
Phase 2146731 to 117
Not applicable863421 to 65
Observational2410052 to 163

When Parkinson's disease trials measure it

Half of the primary outcomes that name Verbal Fluency are measured within 12 weeks of the start, and the middle half from 5 days to 4 months. 40 primary outcomes give a duration.

Latest time point of each outcome

  • Within a day25 outcomes, 10 as a primary outcome
  • Up to 4 weeks19 outcomes, 5 as a primary outcome
  • 1 to 3 months44 outcomes, 13 as a primary outcome
  • 3 to 6 months23 outcomes, 5 as a primary outcome
  • 6 to 12 months8 outcomes, 1 as a primary outcome
  • 1 to 2 years6 outcomes, 3 as a primary outcome
  • Over 2 years7 outcomes, 3 as a primary outcome
  • No duration given8 outcomes, 5 as a primary outcome

A test as a primary outcomeOnly in secondary or other outcomes

132 of the 140 outcome measures give a duration. A single visit counts as within a day.

Status, results, interventions and countries

Status

  • Recruiting27 studies, 14 as a primary outcome
  • Not yet recruiting2 studies, 1 as a primary outcome
  • Active, not recruiting5 studies, 1 as a primary outcome
  • Completed64 studies, 21 as a primary outcome
  • Stopped early10 studies, 3 as a primary outcome
  • Status unknown32 studies, 5 as a primary outcome

What they test

  • Behavioral27 studies, 5 as a primary outcome
  • Drug22 studies, 4 as a primary outcome
  • Device42 studies, 10 as a primary outcome
  • Dietary supplement2 studies, 1 as a primary outcome
  • Procedure7 studies, 2 as a primary outcome
  • Diagnostic test10 studies, 7 as a primary outcome
  • Biological1 studies, 1 as a primary outcome
  • Radiation2 studies, 2 as a primary outcome
  • Genetic2 studies, 1 as a primary outcome
  • Other47 studies, 20 as a primary outcome
  • None given6 studies, 3 as a primary outcome

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

Where their sites are

  • United States46 studies, 19 as a primary outcome
  • Brazil12 studies, 4 as a primary outcome
  • Italy12 studies, 3 as a primary outcome
  • Canada8 studies, 1 as a primary outcome
  • Netherlands8 studies, 0 as a primary outcome
  • Türkiye8 studies, 5 as a primary outcome
  • Sweden7 studies, 1 as a primary outcome
  • Taiwan7 studies, 0 as a primary outcome
  • United Kingdom7 studies, 2 as a primary outcome
  • China6 studies, 2 as a primary outcome
  • Germany6 studies, 1 as a primary outcome
  • Spain6 studies, 3 as a primary outcome

32 countries in all. A study with sites in several counts in each; 6 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 Parkinson's disease studies that name Verbal Fluency: 33 of 64, 52%

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

Completed Parkinson's disease studies that name Verbal Fluency and every completed study, by how they reported results
ResultsCompleted Parkinson's disease studies that name Verbal FluencyEvery completed study
Results on ClinicalTrials.gov and a paper9, 14%776, 10%
Results on ClinicalTrials.gov only13, 20%1,139, 14%
A results paper only11, 17%1,711, 22%
Neither31, 48%4,327, 54%

The 140 studies

Filter by phase, sponsor, status, country, intervention, outcome list, size and start year. Each study links to its record on ClinicalTrials.gov.
ConditionParkinson's disease
TestVerbal Fluency

140 studies match. 45 name Verbal Fluency in a primary outcome. Median size 44 participants. Median time to the primary outcome: 12 weeks.

Loading 140 studies; the filters turn on when they arrive.

By start year
0510152000: 0 studies, 0 naming Verbal Fluency in a primary outcome20002001: 0 studies, 0 naming Verbal Fluency in a primary outcome2002: 0 studies, 0 naming Verbal Fluency in a primary outcome2003: 0 studies, 0 naming Verbal Fluency in a primary outcome2004: 1 studies, 0 naming Verbal Fluency in a primary outcome2005: 0 studies, 0 naming Verbal Fluency in a primary outcome20052006: 0 studies, 0 naming Verbal Fluency in a primary outcome2007: 0 studies, 0 naming Verbal Fluency in a primary outcome2008: 0 studies, 0 naming Verbal Fluency in a primary outcome2009: 0 studies, 0 naming Verbal Fluency in a primary outcome2010: 1 studies, 0 naming Verbal Fluency in a primary outcome20102011: 3 studies, 1 naming Verbal Fluency in a primary outcome2012: 4 studies, 1 naming Verbal Fluency in a primary outcome2013: 4 studies, 0 naming Verbal Fluency in a primary outcome2014: 6 studies, 2 naming Verbal Fluency in a primary outcome2015: 2 studies, 0 naming Verbal Fluency in a primary outcome20152016: 7 studies, 1 naming Verbal Fluency in a primary outcome2017: 12 studies, 2 naming Verbal Fluency in a primary outcome2018: 12 studies, 2 naming Verbal Fluency in a primary outcome2019: 10 studies, 6 naming Verbal Fluency in a primary outcome2020: 12 studies, 5 naming Verbal Fluency in a primary outcome20202021: 14 studies, 5 naming Verbal Fluency in a primary outcome2022: 12 studies, 2 naming Verbal Fluency in a primary outcome2023: 10 studies, 6 naming Verbal Fluency in a primary outcome2024: 9 studies, 4 naming Verbal Fluency in a primary outcome2025: 10 studies, 4 naming Verbal Fluency in a primary outcome20252026: 11 studies, 4 naming Verbal Fluency 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
200410
200500
200600
200700
200800
200900
201010
201131
201241
201340
201462
201520
201671
2017122
2018122
2019106
2020125
2021145
2022122
2023106
202494
2025104
2026114

Library tests named most

  • Verbal Fluency140 studies, 45 as a primary outcome
  • Trail Making Test50 studies, 10 as a primary outcome
  • Digit Span Test43 studies, 6 as a primary outcome
  • Stroop Color-Word Test42 studies, 11 as a primary outcome
  • Verbal Learning33 studies, 11 as a primary outcome
  • Category Fluency29 studies, 10 as a primary outcome
  • Picture Naming Test25 studies, 2 as a primary outcome
  • Clock Drawing Task18 studies, 3 as a primary outcome
  • Symbol Coding17 studies, 4 as a primary outcome
  • Line Angle Matching15 studies, 3 as a primary outcome

Largest condition groups

  • Parkinson's disease140 studies, 45 as a primary outcome
  • Dementia and Alzheimer's12 studies, 6 as a primary outcome
  • Mild cognitive impairment11 studies, 2 as a primary outcome
  • Depression and bipolar disorder8 studies, 0 as a primary outcome
  • Aging, frailty and exercise8 studies, 1 as a primary outcome
  • Stroke5 studies, 1 as a primary outcome
  • Multiple sclerosis4 studies, 1 as a primary outcome
  • Sleep and sleep disorders4 studies, 1 as a primary outcome
  • Cardiovascular disease4 studies, 2 as a primary outcome
  • Brain injury and concussion3 studies, 2 as a primary outcome
  • Anxiety, PTSD and OCD3 studies, 0 as a primary outcome
  • Schizophrenia and psychosis2 studies, 0 as a primary outcome

Phases

Participants

Lead sponsor: industry 9, other 131. Interventional 115, observational 25.

As a primary outcomeSecondary or other outcomeVerbal Fluency

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
NCT07832695Start2026PhaseNot applicableConditionsParkinson's diseaseParticipants90Lead sponsorOtherStatusRecruitingLibrary tests named
  • Verbal FluencySecondary8 weeks
  • Digit Span TestSecondary8 weeks
NCT07815964Start2026PhaseObservationalConditionsParkinson's diseaseParticipants100Lead sponsorOtherStatusNot yet recruitingLibrary tests named
  • Verbal FluencyPrimary
NCT07777419Start2026PhaseNot applicableConditionsParkinson's diseaseParticipants20Lead sponsorOtherStatusRecruitingLibrary tests named
  • Stroop Color-Word TestSecondarysame day
  • Verbal FluencyPrimarysame day
  • Go/No-Go TaskSecondarysame day
  • Category FluencyPrimarysame day
NCT07678983Start2026PhaseNot applicableConditionsParkinson's diseaseParticipants66Lead sponsorOtherStatusActive, not recruitingLibrary tests named
  • Trail Making TestSecondary8 weeks
  • Stroop Color-Word TestSecondary8 weeks
  • Verbal FluencySecondary8 weeks
  • Digit Span TestSecondary8 weeks
  • Category FluencySecondary8 weeks
NCT07651085Start2024PhaseObservationalConditionsDementia and Alzheimer's, Mild cognitive impairment, Parkinson's disease, Sleep and sleep disordersParticipants65Lead sponsorOtherStatusActive, not recruitingLibrary tests named
  • Verbal LearningPrimary
  • Verbal FluencyPrimary
  • Category FluencyPrimary
  • Clock Drawing TaskPrimary
NCT07569120Start2026PhaseNot applicableConditionsParkinson's disease, Healthy volunteers, Aging, frailty and exerciseParticipants165Lead sponsorOtherStatusRecruitingLibrary tests named
  • Trail Making TestSecondary2 days
  • Verbal FluencySecondary2 days
  • Digit Span TestSecondary2 days
  • Category FluencySecondary2 days
  • Tower PlanningSecondary2 days
NCT07536022Start2026PhaseNot applicableConditionsParkinson's diseaseParticipants16Lead sponsorOtherStatusRecruitingLibrary tests named
  • Stroop Color-Word TestOther outcome8 weeks
  • Verbal FluencyOther outcome8 weeks
  • Digit Span TestOther outcome8 weeks
NCT07534397Start2026PhaseNot applicableConditionsParkinson's diseaseParticipants20Lead sponsorOtherStatusRecruitingLibrary tests named
  • Verbal FluencyPrimary6 weeks
  • Category FluencyPrimary6 weeks
NCT07456475Start2025PhaseNot applicableConditionsStroke, Brain injury and concussion, Parkinson's disease, Multiple sclerosisParticipants25Lead sponsorOtherStatusActive, not recruitingLibrary tests named
  • Verbal FluencySecondary6 weeks
NCT07355842Start2026PhaseNot applicableConditionsParkinson's disease, Sleep and sleep disordersParticipants80Lead sponsorOtherStatusRecruitingLibrary tests named
  • Trail Making TestSecondary18 months
  • Stroop Color-Word TestSecondary18 months
  • Verbal LearningSecondary18 months
  • Verbal FluencySecondary18 months
  • Digit Span TestSecondary18 months
  • Category FluencySecondary18 months
  • Picture Naming TestSecondary18 months
  • Psychomotor Vigilance TaskOther outcome18 months
  • Complex Figure Copy and RecallSecondary18 months
  • Finger Tapping TaskSecondary18 months
  • Sustained Attention to ResponseOther outcome18 months
  • Line Angle MatchingSecondary18 months
NCT07340073Start2026PhasePhase 1ConditionsParkinson's diseaseParticipants24Lead sponsorOtherStatusNot yet recruitingLibrary tests named
  • Trail Making TestSecondary9 weeks
  • Verbal FluencySecondary9 weeks
  • N-Back TaskSecondary9 weeks
NCT07277205Start2026PhaseNot applicableConditionsParkinson's diseaseParticipants45Lead sponsorOtherStatusRecruitingLibrary tests named
  • Verbal FluencyPrimary8 weeks
  • Digit Span TestSecondary8 weeks
  • Category FluencyPrimary8 weeks
  • Clock Drawing TaskSecondary8 weeks
NCT07262658Start2022PhaseObservationalConditionsParkinson's diseaseParticipants40Lead sponsorOtherStatusCompletedLibrary tests named
  • Trail Making TestPrimarysame day
  • Verbal LearningPrimarysame day
  • Verbal FluencyPrimarysame day
  • Category FluencyPrimarysame day
  • Card Sorting Test (Berg)Primarysame day
  • Paced Visual Serial Addition TestPrimarysame day
  • Symbol Scan TaskPrimarysame day
NCT07240272Start2023PhaseNot applicableConditionsParkinson's diseaseParticipants28Lead sponsorOtherStatusCompleted

Paper

Library tests named
  • Trail Making TestPrimary13 weeks
  • Verbal FluencyPrimary13 weeks
  • Digit Span TestPrimary13 weeks
  • Category FluencyPrimary13 weeks
NCT07154511Start2025PhasePhase 1/2ConditionsDementia and Alzheimer's, Parkinson's diseaseParticipants45Lead sponsorOtherStatusRecruitingLibrary tests named
  • Trail Making TestPrimary14 weeks
  • Verbal LearningPrimary14 weeks
  • Verbal FluencyPrimary14 weeks
  • Line Angle MatchingPrimary14 weeks
NCT07058714Start2025PhaseObservationalConditionsParkinson's diseaseParticipants30Lead sponsorOtherStatusCompletedLibrary tests named
  • Verbal FluencySecondarysame day
  • Digit Span TestSecondarysame day
  • Arithmetic Fluency TaskSecondarysame day
NCT07055087Start2026PhasePhase 2ConditionsParkinson's diseaseParticipants120Lead sponsorOtherStatusRecruitingLibrary tests named
  • Trail Making TestSecondary2 years
  • Stroop Color-Word TestSecondary2 years
  • Verbal LearningSecondary2 years
  • Verbal FluencySecondary2 years
  • Category FluencySecondary2 years
  • Picture Naming TestSecondary2 years
  • Short Story RecallSecondary2 years
  • Line Angle MatchingSecondary2 years
NCT06967493Start2025PhaseNot applicableConditionsParkinson's diseaseParticipants80Lead sponsorOtherStatusRecruitingLibrary tests named
  • Verbal FluencyPrimary13 weeks
  • Category FluencyPrimary13 weeks
  • Eriksen Flanker TaskPrimary13 weeks
NCT06960096Start2025PhaseObservationalConditionsParkinson's diseaseParticipants55Lead sponsorOtherStatusRecruitingLibrary tests named
  • Verbal FluencyPrimary14 months
  • Task Switching TestPrimary14 months
NCT06906276Start2025PhaseObservationalConditionsParkinson's disease, Aging, frailty and exerciseParticipants30Lead sponsorOtherStatusRecruitingLibrary tests named
  • Trail Making TestSecondarysame day
  • Stroop Color-Word TestPrimarysame day
  • Verbal LearningSecondarysame day
  • Verbal FluencySecondarysame day
  • Symbol CodingSecondarysame day
NCT06893120Start2022PhaseNot applicableConditionsParkinson's disease, Depression and bipolar disorderParticipants20Lead sponsorOtherStatusCompletedLibrary tests named
  • Verbal FluencySecondary13 weeks
  • Clock Drawing TaskSecondary13 weeks
NCT06823921Start2025PhaseNot applicableConditionsParkinson's diseaseParticipants30Lead sponsorOtherStatusRecruitingLibrary tests named
  • Trail Making TestSecondary6 months
  • Verbal FluencySecondary6 months
NCT06782724Start2025PhasePhase 2ConditionsParkinson's disease, Multiple sclerosis, Depression and bipolar disorder, Lung diseaseParticipants108Lead sponsorOtherStatusRecruitingLibrary tests named
  • Trail Making TestOther outcome8 weeks
  • Verbal LearningOther outcome8 weeks
  • Verbal FluencyOther outcome8 weeks
  • Digit Span TestOther outcome8 weeks
  • Symbol CodingOther outcome8 weeks
NCT06688357Start2019PhaseNot applicableConditionsParkinson's diseaseParticipants23Lead sponsorOtherStatusCompleted

Results

Library tests named
  • Verbal LearningSecondary2 weeks
  • Verbal FluencyPrimary2 weeks
  • N-Back TaskSecondary2 weeks
  • Category FluencyPrimary2 weeks
NCT06657274Start2024PhaseNot applicableConditionsMild cognitive impairment, Parkinson's diseaseParticipants60Lead sponsorOtherStatusRecruitingLibrary tests named
  • Stroop Color-Word TestSecondary13 weeks
  • Verbal FluencySecondary13 weeks
  • Category FluencySecondary13 weeks
  • Complex Figure Copy and RecallSecondary13 weeks
  • Matrix ReasoningSecondary13 weeks
  • Selective Reminding TaskPrimary13 weeks
  • Delayed Recall ModulePrimary13 weeks

Page 1 of 6

Questions, answered from the data

How many Parkinson's disease trials use Verbal Fluency?

140 registered Parkinson's disease studies on ClinicalTrials.gov name it in an outcome measure, 45 of them in a primary outcome: 16% of the condition's 892 studies with a cognitive outcome, against 11% of all of them. It is the 2nd most named test in Parkinson's disease trials.

Which tests do Parkinson's disease trials use with Verbal Fluency?

The Trail Making Test (50 studies), the Digit Span Test (43 studies) and the Stroop Color-Word Test (42 studies).

How many participants do phase 2 Parkinson's disease trials that use Verbal Fluency enroll?

Half of the phase 2 studies that name it enroll 67 participants or fewer, and the middle half enroll 31 to 117. 14 of them give a size.

When do Parkinson's disease trials measure Verbal Fluency?

Half of the primary outcomes that name Verbal Fluency are measured within 12 weeks of the start, and the middle half from 5 days to 4 months. 40 primary outcomes give a duration.

How many completed Parkinson's disease trials that use Verbal Fluency have reported results?

33 of the 64 completed studies that name it, 52%, have reported results: 22 posted them on ClinicalTrials.gov, 20 have a results paper linked to the registry record, and 9 did both. The other 31 show neither. Of all completed studies with a cognitive outcome, 46% have reported results.

More on Verbal Fluency and Parkinson's disease

  • Every cognitive test in Parkinson's disease trials: 892 studies
  • Verbal Fluency in all clinical trials: 1,745 studies

Verbal Fluency in other conditions

  • Dementia and Alzheimer's248
  • Cancer200
  • Mild cognitive impairment177
  • Depression and bipolar disorder154
  • Aging, frailty and exercise136
  • Stroke110
  • Schizophrenia and psychosis107
  • Brain injury and concussion86
  • Cognitive impairment and decline63
  • Obesity and diabetes63
  • Anxiety, PTSD and OCD61
  • Cardiovascular disease61
  • Multiple sclerosis58
  • Sleep and sleep disorders58
  • Pain and fatigue53

Other tests in Parkinson's disease trials

  • Trail Making Test156
  • Stroop Color-Word Test126
  • Digit Span Test86
  • Verbal Learning61

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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