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  1. Home
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  3. /Clinical trials
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  5. /Healthy volunteers
  6. /Symbol Coding

Clinical trials data

Symbol Coding in healthy volunteer trials: 56 registered studies

Every registered healthy volunteers study on ClinicalTrials.gov that names Symbol Coding 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 healthy volunteers studies name it in an outcome measure
56
Name it in a primary outcome, 32%
18 of 56
Of the condition's 656 studies name it, against 9% of all registered studies
9%
Other conditions
Median participants per study
57
By phase
Try the Symbol Key GameTry Symbol Coding

Tests named in the same studies

The library tests that healthy volunteers studies naming Symbol Coding name most often beside it.
  1. 1

    Trail Making Test8 studies, 3 as a primary outcome

  2. 2

    Stroop Color-Word Test8 studies, 2 as a primary outcome

  3. 3

    Digit Span Test6 studies, 4 as a primary outcome

  4. 4

    Verbal Learning5 studies, 3 as a primary outcome

  5. 5

    Psychomotor Vigilance Task5 studies, 1 as a primary outcome

  6. 6

    Verbal Fluency4 studies, 1 as a primary outcome

  7. 7

    Matrix Reasoning3 studies, 2 as a primary outcome

  8. 8

    Paired Associate Learning3 studies, 2 as a primary outcome

  9. 9

    Selective Reminding Task3 studies, 2 as a primary outcome

  10. 10

    Task Switching Test3 studies, 2 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: 0 studies, 0 with a test as a primary outcome2005: 0 studies, 0 with a test as a primary outcome20052006: 1 studies, 1 with a test as a primary outcome2007: 1 studies, 0 with a test as a primary outcome2008: 1 studies, 0 with a test as a primary outcome2009: 0 studies, 0 with a test as a primary outcome2010: 2 studies, 2 with a test as a primary outcome20102011: 4 studies, 0 with a test as a primary outcome2012: 0 studies, 0 with a test as a primary outcome2013: 2 studies, 1 with a test as a primary outcome2014: 2 studies, 1 with a test as a primary outcome2015: 0 studies, 0 with a test as a primary outcome20152016: 2 studies, 0 with a test as a primary outcome2017: 2 studies, 1 with a test as a primary outcome2018: 4 studies, 2 with a test as a primary outcome2019: 1 studies, 1 with a test as a primary outcome2020: 3 studies, 0 with a test as a primary outcome20202021: 4 studies, 2 with a test as a primary outcome2022: 3 studies, 2 with a test as a primary outcome2023: 2 studies, 1 with a test as a primary outcome2024: 6 studies, 1 with a test as a primary outcome2025: 13 studies, 3 with a test as a primary outcome20252026: 3 studies, 0 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
200611
200710
200810
200900
201022
201140
201200
201321
201421
201500
201620
201721
201842
201911
202030
202142
202232
202321
202461
2025133
202630

Phases and study sizes

By phase

  • Early phase 12 studies, 1 as a primary outcome
  • Phase 118 studies, 2 as a primary outcome
  • Phase 1/21 studies, 0 as a primary outcome
  • Phase 21 studies, 0 as a primary outcome
  • Phase 32 studies, 1 as a primary outcome
  • Phase 44 studies, 0 as a primary outcome
  • Not applicable22 studies, 11 as a primary outcome
  • Observational6 studies, 3 as a primary outcome

Participants per study

102050100
  • Phase 124 median, 12 to 46
  • Not applicable74 median, 31 to 120
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 healthy volunteers study that names Symbol Coding, by phase
PhaseStudies with a sizeMedianMiddle half
Phase 1172412 to 46
Not applicable227431 to 120

When healthy volunteer trials measure it

Half of the primary outcomes that name Symbol Coding are measured within 5 weeks of the start, and the middle half from the first day to 10 weeks. 18 primary outcomes give a duration.

Latest time point of each outcome

  • Within a day21 outcomes, 6 as a primary outcome
  • Up to 4 weeks11 outcomes, 3 as a primary outcome
  • 1 to 3 months15 outcomes, 7 as a primary outcome
  • 3 to 6 months3 outcomes, 1 as a primary outcome
  • 6 to 12 months4 outcomes, 0 as a primary outcome
  • 1 to 2 years1 outcomes, 1 as a primary outcome
  • No duration given1 outcomes, 0 as a primary outcome

A test as a primary outcomeOnly in secondary or other outcomes

55 of the 56 outcome measures give a duration. A single visit counts as within a day.

Status, results, interventions and countries

Status

  • Recruiting12 studies, 2 as a primary outcome
  • Active, not recruiting2 studies, 1 as a primary outcome
  • Completed33 studies, 12 as a primary outcome
  • Stopped early2 studies, 1 as a primary outcome
  • Status unknown7 studies, 2 as a primary outcome

What they test

  • Behavioral10 studies, 6 as a primary outcome
  • Drug29 studies, 4 as a primary outcome
  • Device3 studies, 2 as a primary outcome
  • Dietary supplement7 studies, 2 as a primary outcome
  • Procedure1 studies, 1 as a primary outcome
  • Diagnostic test2 studies, 1 as a primary outcome
  • Other6 studies, 3 as a primary outcome
  • None given4 studies, 1 as a primary outcome

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

Where their sites are

  • United States20 studies, 11 as a primary outcome
  • United Kingdom5 studies, 0 as a primary outcome
  • Denmark4 studies, 0 as a primary outcome
  • Finland4 studies, 0 as a primary outcome
  • Spain4 studies, 0 as a primary outcome
  • Belgium3 studies, 1 as a primary outcome
  • Italy3 studies, 2 as a primary outcome
  • Canada2 studies, 0 as a primary outcome
  • France2 studies, 1 as a primary outcome
  • Germany2 studies, 0 as a primary outcome
  • Hungary2 studies, 1 as a primary outcome
  • Netherlands2 studies, 0 as a primary outcome

19 countries in all. A study with sites in several counts in each; 1 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 healthy volunteers studies that name Symbol Coding: 7 of 33, 21%

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

Completed healthy volunteers studies that name Symbol Coding and every completed study, by how they reported results
ResultsCompleted healthy volunteers studies that name Symbol CodingEvery completed study
Results on ClinicalTrials.gov and a paper2, 6%776, 10%
Results on ClinicalTrials.gov only2, 6%1,139, 14%
A results paper only3, 9%1,711, 22%
Neither26, 79%4,327, 54%

The 56 studies

Filter by phase, sponsor, status, country, intervention, outcome list, size and start year. Each study links to its record on ClinicalTrials.gov.
ConditionHealthy volunteers
TestSymbol Coding

56 studies match. 18 name Symbol Coding in a primary outcome. Median size 57 participants. Median time to the primary outcome: 5 weeks.

Loading 56 studies; the filters turn on when they arrive.

By start year
0510152000: 0 studies, 0 naming Symbol Coding in a primary outcome20002001: 0 studies, 0 naming Symbol Coding in a primary outcome2002: 0 studies, 0 naming Symbol Coding in a primary outcome2003: 0 studies, 0 naming Symbol Coding in a primary outcome2004: 0 studies, 0 naming Symbol Coding in a primary outcome2005: 0 studies, 0 naming Symbol Coding in a primary outcome20052006: 1 studies, 1 naming Symbol Coding in a primary outcome2007: 1 studies, 0 naming Symbol Coding in a primary outcome2008: 1 studies, 0 naming Symbol Coding in a primary outcome2009: 0 studies, 0 naming Symbol Coding in a primary outcome2010: 2 studies, 2 naming Symbol Coding in a primary outcome20102011: 4 studies, 0 naming Symbol Coding in a primary outcome2012: 0 studies, 0 naming Symbol Coding in a primary outcome2013: 2 studies, 1 naming Symbol Coding in a primary outcome2014: 2 studies, 1 naming Symbol Coding in a primary outcome2015: 0 studies, 0 naming Symbol Coding in a primary outcome20152016: 2 studies, 0 naming Symbol Coding in a primary outcome2017: 2 studies, 1 naming Symbol Coding in a primary outcome2018: 4 studies, 2 naming Symbol Coding in a primary outcome2019: 1 studies, 1 naming Symbol Coding in a primary outcome2020: 3 studies, 0 naming Symbol Coding in a primary outcome20202021: 4 studies, 2 naming Symbol Coding in a primary outcome2022: 3 studies, 2 naming Symbol Coding in a primary outcome2023: 2 studies, 1 naming Symbol Coding in a primary outcome2024: 6 studies, 1 naming Symbol Coding in a primary outcome2025: 13 studies, 3 naming Symbol Coding in a primary outcome20252026: 3 studies, 0 naming Symbol Coding 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
200611
200710
200810
200900
201022
201140
201200
201321
201421
201500
201620
201721
201842
201911
202030
202142
202232
202321
202461
2025133
202630

Library tests named most

  • Symbol Coding56 studies, 18 as a primary outcome
  • Trail Making Test8 studies, 3 as a primary outcome
  • Stroop Color-Word Test8 studies, 2 as a primary outcome
  • Digit Span Test6 studies, 4 as a primary outcome
  • Verbal Learning5 studies, 3 as a primary outcome
  • Psychomotor Vigilance Task5 studies, 1 as a primary outcome
  • Verbal Fluency4 studies, 1 as a primary outcome
  • Matrix Reasoning3 studies, 2 as a primary outcome
  • Paired Associate Learning3 studies, 2 as a primary outcome
  • Selective Reminding Task3 studies, 2 as a primary outcome

Conditions

  • Healthy volunteers56 studies, 18 as a primary outcome
  • Aging, frailty and exercise12 studies, 5 as a primary outcome
  • Multiple sclerosis4 studies, 0 as a primary outcome
  • Schizophrenia and psychosis2 studies, 1 as a primary outcome
  • Substance use and addiction2 studies, 0 as a primary outcome
  • Sleep and sleep disorders2 studies, 0 as a primary outcome
  • Parkinson's disease1 study, 0 as a primary outcome
  • Depression and bipolar disorder1 study, 0 as a primary outcome
  • COVID-19 and long COVID1 study, 0 as a primary outcome
  • Anxiety, PTSD and OCD1 study, 0 as a primary outcome
  • Pain and fatigue1 study, 0 as a primary outcome

Phases

Participants

Lead sponsor: industry 17, other 39. Interventional 50, observational 6.

As a primary outcomeSecondary or other outcomeSymbol Coding

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
NCT07827651Start2025PhaseNot applicableConditionsHealthy volunteers, Aging, frailty and exercise, Sleep and sleep disordersParticipants64Lead sponsorIndustryStatusActive, not recruitingLibrary tests named
  • Symbol CodingSecondary12 weeks
NCT07783074Start2026PhaseObservationalConditionsMultiple sclerosis, Healthy volunteers, COVID-19 and long COVID, Pain and fatigueParticipants122Lead sponsorOtherStatusRecruitingLibrary tests named
  • Symbol CodingSecondary9 weeks
  • Finger Tapping TaskPrimary9 weeks
NCT07623122Start2024PhaseNot applicableConditionsHealthy volunteers, Aging, frailty and exerciseParticipants120Lead sponsorOtherStatusCompletedLibrary tests named
  • Trail Making TestSecondary4 weeks
  • Symbol CodingSecondary4 weeks
  • Clock Drawing TaskSecondary4 weeks
NCT07580820Start2025PhaseObservationalConditionsMultiple sclerosis, Healthy volunteersParticipants32Lead sponsorOtherStatusRecruitingLibrary tests named
  • Symbol CodingOther outcomesame day
NCT07511439Start2026PhasePhase 4ConditionsHealthy volunteersParticipants60Lead sponsorOtherStatusRecruitingLibrary tests named
  • Trail Making TestOther outcome12 months
  • Verbal FluencyOther outcome12 months
  • Symbol CodingOther outcome12 months
  • Complex Figure Copy and RecallOther outcome12 months
  • Simple Reaction TimeOther outcome12 months
  • Emoji Emotion RecognitionOther outcome12 months
  • Letter-Number Sequencing TaskOther outcome12 months
  • Probabilistic Reversal LearningOther outcome12 months
  • Intra/Extra Dimensional Set ShiftOther outcome12 months
NCT07505355Start2025PhaseObservationalConditionsMultiple sclerosis, Healthy volunteersParticipants100Lead sponsorOtherStatusRecruitingLibrary tests named
  • Symbol CodingOther outcomesame day
NCT07267845Start2025PhaseNot applicableConditionsHealthy volunteersParticipants80Lead sponsorOtherStatusRecruitingLibrary tests named
  • Stroop Color-Word TestPrimary6 weeks
  • Symbol CodingSecondary6 weeks
  • Go/No-Go TaskSecondary6 weeks
  • Sustained Attention to ResponseSecondary6 weeks
NCT07231497Start2025PhasePhase 3ConditionsSchizophrenia and psychosis, Healthy volunteersParticipants103Lead sponsorOtherStatusRecruitingLibrary tests named
  • Symbol CodingPrimarysame day
  • Matrix ReasoningPrimarysame day
  • AX Continuous Performance TestPrimary1 week
  • Word Pair LearningPrimarysame day
  • Four-Armed BanditPrimary1 week
NCT07208279Start2025PhaseNot applicableConditionsHealthy volunteers, Aging, frailty and exerciseParticipants16Lead sponsorOtherStatusRecruitingLibrary tests named
  • Verbal LearningPrimary6 weeks
  • Digit Span TestPrimary6 weeks
  • Symbol CodingPrimary6 weeks
NCT07195318Start2025PhaseNot applicableConditionsHealthy volunteersParticipants120Lead sponsorOtherStatusRecruitingLibrary tests named
  • Symbol CodingOther outcome7 weeks
NCT07161518Start2025PhasePhase 4ConditionsHealthy volunteersParticipants10Lead sponsorOtherStatusRecruitingLibrary tests named
  • Symbol CodingSecondarysame day
  • Psychomotor Vigilance TaskSecondarysame day
NCT07119684Start2024PhaseNot applicableConditionsHealthy volunteersParticipants35Lead sponsorOtherStatusCompletedLibrary tests named
  • Stroop Color-Word TestSecondary6 weeks
  • Symbol CodingPrimary6 weeks
NCT07110896Start2025PhaseNot applicableConditionsHealthy volunteers, Aging, frailty and exercise, Anxiety, PTSD and OCDParticipants236Lead sponsorIndustryStatusRecruitingLibrary tests named
  • Symbol CodingSecondary13 weeks
NCT07109245Start2025PhasePhase 4ConditionsHealthy volunteersParticipants35Lead sponsorOtherStatusRecruitingLibrary tests named
  • Symbol CodingSecondary5 months
NCT07050368Start2025PhasePhase 1ConditionsHealthy volunteersParticipants20Lead sponsorIndustryStatusCompletedLibrary tests named
  • Trail Making TestOther outcome2 weeks
  • Symbol CodingOther outcome2 weeks
NCT07043452Start2025PhaseEarly phase 1ConditionsHealthy volunteersParticipantsNot givenLead sponsorOtherStatusStopped earlyLibrary tests named
  • Symbol CodingPrimarysame day
NCT06931977Start2025PhaseNot applicableConditionsHealthy volunteersParticipants97Lead sponsorIndustryStatusCompletedLibrary tests named
  • Symbol CodingSecondary12 weeks
NCT06643637Start2024PhasePhase 1ConditionsHealthy volunteersParticipants16Lead sponsorIndustryStatusCompletedLibrary tests named
  • Trail Making TestSecondary2 weeks
  • Stroop Color-Word TestSecondary2 weeks
  • Symbol CodingSecondary2 weeks
NCT06616285Start2024PhaseNot applicableConditionsHealthy volunteers, Aging, frailty and exerciseParticipants80Lead sponsorOtherStatusStatus unknownLibrary tests named
  • Trail Making TestSecondary6 months
  • Stroop Color-Word TestSecondary6 months
  • Verbal FluencySecondary6 months
  • Digit Span TestSecondary6 months
  • Symbol CodingSecondary6 months
  • Probabilistic Reversal LearningSecondary6 months
  • Effort Discounting TaskSecondary6 months
NCT06570369Start2024PhasePhase 1ConditionsDepression and bipolar disorder, Healthy volunteersParticipants26Lead sponsorIndustryStatusCompletedLibrary tests named
  • Symbol CodingSecondary2 weeks
  • Paired Associate LearningSecondary2 weeks
  • Spatial Working MemorySecondary2 weeks
NCT06431932Start2026PhasePhase 1/2ConditionsHealthy volunteersParticipants60Lead sponsorOtherStatusRecruitingLibrary tests named
  • Symbol CodingSecondary12 weeks
NCT06425679Start2023PhaseNot applicableConditionsHealthy volunteers, Aging, frailty and exerciseParticipants120Lead sponsorOtherStatusStatus unknownLibrary tests named
  • Trail Making TestPrimary11 months
  • Stroop Color-Word TestSecondary11 months
  • Digit Span TestSecondary11 months
  • Symbol CodingSecondary11 months
  • Clock Drawing TaskSecondary11 months
NCT06066281Start2023PhaseObservationalConditionsHealthy volunteersParticipants480Lead sponsorOtherStatusStatus unknownLibrary tests named
  • Digit Span TestPrimary2 years
  • Symbol CodingPrimary2 years
  • Paced Visual Serial Addition TestPrimary2 years
  • Selective Reminding TaskPrimary2 years
NCT05974605Start2022PhaseNot applicableConditionsHealthy volunteers, Aging, frailty and exerciseParticipants16Lead sponsorOtherStatusCompletedLibrary tests named
  • Verbal LearningPrimary10 weeks
  • Symbol CodingPrimary10 weeks
  • N-Back TaskPrimary10 weeks
  • Task Switching TestPrimary10 weeks
  • Short Story RecallPrimary10 weeks
  • Matrix ReasoningPrimary10 weeks
  • Size Order Memory TestPrimary10 weeks
  • Picture Order Memory TestPrimary10 weeks
  • Mnemonic Similarity TaskPrimary10 weeks
NCT05826314Start2022PhaseNot applicableConditionsHealthy volunteersParticipants75Lead sponsorOtherStatusCompletedLibrary tests named
  • Stroop Color-Word TestPrimary6 months
  • Symbol CodingPrimary6 months

Page 1 of 3

Questions, answered from the data

How many healthy volunteer trials use Symbol Coding?

56 registered healthy volunteers studies on ClinicalTrials.gov name it in an outcome measure, 18 of them in a primary outcome: 9% of the condition's 656 studies with a cognitive outcome, against 9% of all of them. It is the 5th most named test in healthy volunteer trials.

Which tests do healthy volunteer trials use with Symbol Coding?

The Trail Making Test (8 studies), the Stroop Color-Word Test (8 studies) and the Digit Span Test (6 studies).

When do healthy volunteer trials measure Symbol Coding?

Half of the primary outcomes that name Symbol Coding are measured within 5 weeks of the start, and the middle half from the first day to 10 weeks. 18 primary outcomes give a duration.

How many completed healthy volunteer trials that use Symbol Coding have reported results?

7 of the 33 completed studies that name it, 21%, have reported results: 4 posted them on ClinicalTrials.gov, 5 have a results paper linked to the registry record, and 2 did both. The other 26 show neither. Of all completed studies with a cognitive outcome, 46% have reported results.

More on Symbol Coding and healthy volunteers

  • Every cognitive test in healthy volunteer trials: 656 studies
  • Symbol Coding in all clinical trials: 1,457 studies

Symbol Coding in other conditions

  • Multiple sclerosis375
  • Depression and bipolar disorder143
  • Dementia and Alzheimer's117
  • Aging, frailty and exercise116
  • Sleep and sleep disorders89
  • Mild cognitive impairment84
  • Pain and fatigue82
  • Stroke61
  • Substance use and addiction60
  • Obesity and diabetes59
  • Cancer58

Other tests in healthy volunteer trials

  • Stroop Color-Word Test98
  • Trail Making Test68
  • Digit Span Test64
  • Verbal Learning56
  • N-Back Task51

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.

The census counts Symbol Key Game and Symbol Coding as one test family, so this page counts their studies together.

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