Clinical Cohort Protocol Designer

This skill must not confuse cohort protocol design with case-control design, cross-sectional design, randomized trial design, or pure biomarker discovery without cohort logic.

Reference Module Integration

The references/ directory is not optional background material. It defines the operational rules that must be actively used while running this skill.

Use the reference modules as follows:

• references/cohort-question-fit-rules.md → use when judging whether a cohort design is appropriate in Section B.
• references/cohort-type-selection-framework.md → use when choosing retrospective versus prospective cohort structure in Section C.
• references/time-zero-and-follow-up-rules.md → use when defining index date, baseline window, follow-up start, censoring, and observation windows in Sections D–E.
• references/enrollment-and-eligibility-framework.md → use when writing source population, inclusion criteria, exclusion criteria, and enrollment logic in Section D.
• references/endpoint-definition-framework.md → use when defining primary and secondary outcomes in Section F.
• references/variable-collection-taxonomy.md → use when structuring covariates, exposures, predictors, confounders, effect modifiers, and follow-up variables in Section G.
• references/analysis-line-framework.md → use when building the main statistical analysis line in Section H.
• references/bias-and-validity-review-rules.md → use when identifying internal validity threats and design limitations in Section I.
• references/feasibility-and-data-quality-rules.md → use when distinguishing available versus missing variables, follow-up completeness, and ascertainment burden in Section J.
• references/output-section-guidance.md → use to keep the final report sectioned, bounded, and decision-oriented across Sections A–L.
• references/literature-integrity-rules.md → use whenever referring to prior cohort precedents, clinical variable availability, guideline practice, registries, event rates, follow-up assumptions, or published evidence.
• references/workflow-step-template.md → use to keep the workflow sequencing explicit and consistent.

If any output section is generated without using its corresponding reference module, the output should be treated as incomplete.

Input Validation

Valid input usually includes one or more of the following:

• a disease / population plus exposure or predictor plus outcome idea
• a prognostic or treatment-response question suitable for longitudinal follow-up
• a real-world evidence question involving routine clinical data
• a biomarker or risk factor question that needs cohort structuring
• a request to design a retrospective or prospective cohort study
• a partially defined clinical protocol needing enrollment, follow-up, endpoint, and analysis logic

Examples:

• “Design a retrospective cohort study to assess whether baseline sarcopenia predicts survival after immunotherapy.”
• “Help me build a prospective cohort protocol for postoperative delirium risk in older surgical patients.”
• “I want a clinical cohort study on ctDNA and recurrence in colorectal cancer.”
• “Can you structure a hospital-based cohort for AKI and long-term mortality?”
• “We have EHR data and want to study whether early steroid exposure affects infection risk.”

Out-of-scope — respond with the redirect below and stop:

• direct patient-specific diagnostic or treatment advice
• a request that is really a randomized trial protocol
• a question better answered by case-control, cross-sectional, diagnostic accuracy, or mechanistic experimental design without cohort logic
• pure literature review requests with no protocol-design purpose

“This skill is designed to build retrospective or prospective clinical cohort study protocols. Your request ([restatement]) is outside that scope because it requires [patient-specific medical advice / a different study design family / a completed evidence answer rather than cohort protocol design].”

Sample Triggers

• “Design a retrospective clinical cohort protocol for this question.”
• “Should this be a retrospective or prospective cohort?”
• “Help me define inclusion criteria, follow-up, and endpoints for a cohort study.”
• “We have hospital records. How do we structure a cohort protocol?”
• “I want a prognostic cohort design with a clear statistical main line.”
• “Can you build the variable collection and endpoint framework for this clinical cohort study?”

Core Function

This skill should:

1. determine whether a cohort design is actually appropriate
2. classify the intended cohort design type
3. define the target question, source population, and analytic target population
4. specify time-zero, baseline window, enrollment logic, and follow-up structure
5. define primary and secondary endpoints with ascertainment logic
6. structure the variable collection framework
7. select the main statistical analysis line appropriate to the endpoint structure
8. identify confounding, bias, missingness, and validity threats
9. distinguish design elements that are core, recommended, optional, or assumption-dependent
10. recommend the best cohort protocol version for the user’s objective and likely data reality

This skill should not:

• default to causal language when the design only supports association
• place post-baseline variables into the baseline adjustment set without warning
• assume complete follow-up or uniform measurement quality
• pretend that every question should become a prospective cohort
• overbuild a protocol with every possible variable and endpoint if the main line is still unclear

Clarification Rule

If the user has not adequately specified the cohort question, this skill must clarify the minimum items needed before locking the design:

• disease / condition / clinical setting
• target population
• exposure, predictor, or baseline factor of interest
• intended outcome or endpoint family
• retrospective versus prospective preference, if any
• likely data source or recruitment setting
• approximate follow-up horizon

If critical inputs are missing, ask 2–6 concise, high-yield follow-up questions.

Do not ask a long questionnaire if a narrower set of questions would establish:

• whether a cohort design is appropriate
• where time-zero should be set
• what the primary endpoint is
• what follow-up structure is needed

If the user wants a one-shot protocol framework, proceed with explicit assumptions and label assumption-dependent elements clearly.

Supported Cohort Study Families

The skill must first identify the dominant cohort family. Typical families include:

• retrospective EHR or chart-review cohort
• retrospective registry-based cohort
• claims / administrative-data cohort
• prospective observational clinical cohort
• prospective biomarker-enriched cohort
• hospital-based disease cohort
• treatment-exposure cohort for comparative effectiveness or safety
• prognosis / risk-prediction cohort
• survivorship or recurrence-follow-up cohort
• multi-center observational cohort

If the user’s idea could fit more than one cohort family, explicitly identify the lead family and the main alternative.

Cohort Design Selection Logic

Choose the design form based on the research question, data capture reality, and outcome timing, not by habit.

Typical mappings:

• Retrospective cohort → existing EHR, registry, claims, or chart data with historical exposure and follow-up already accrued
• Prospective cohort → future enrollment, standardized variable collection, biomarker sampling, or protocolized follow-up needed
• Exposure cohort → treatment / medication / intervention exposure observed in routine care
• Prognostic cohort → baseline clinical or molecular factor predicting future outcome
• Safety cohort → adverse outcome incidence after a clinical exposure
• Natural history cohort → progression, recurrence, mortality, or longitudinal disease burden description
• Biomarker cohort → baseline marker or signature linked to future outcome, often requiring pre-specified collection procedures

Never choose a prospective design just because it seems stronger if the user lacks realistic recruitment or follow-up capacity. Never choose a retrospective design without checking whether time-zero and exposure ascertainment can be defined coherently.

Execution

Step 1 — Define the actual cohort question

Identify the true protocol objective.

Clarify whether the study is primarily about:

• prognosis
• risk factor association
• treatment effectiveness
• treatment safety
• recurrence / progression
• biomarker prediction
• natural history
• health-services or practice-variation outcomes

State the dominant objective and any secondary objectives.

Step 2 — Decide whether cohort design is appropriate

Use references/cohort-question-fit-rules.md to judge whether a cohort design fits the temporal logic of the question.

State:

• why a cohort design fits
• whether another design family might compete
• whether the intended interpretation is mainly descriptive, associative, predictive, or quasi-causal

Step 3 — Select the cohort type

Use references/cohort-type-selection-framework.md to select retrospective or prospective structure and the most likely data-source family.

State:

• recommended cohort type
• why it should lead
• what alternative cohort form could be considered
• what trade-off is being accepted

Step 4 — Define source population, eligibility, and time-zero

Use references/enrollment-and-eligibility-framework.md and references/time-zero-and-follow-up-rules.md.

Specify:

• source population
• recruitment or sampling frame
• inclusion criteria
• exclusion criteria
• index date / time-zero
• baseline assessment window
• cohort entry rule
• handling of repeat entries or multiple episodes if relevant

Do not allow vague eligibility logic.

Step 5 — Define follow-up structure

Specify:

• follow-up start
• follow-up duration or observation horizon
• visit schedule or data-capture rhythm if prospective
• censoring rules
• loss-to-follow-up handling concept
• competing events if relevant

Do not mix fixed-horizon outcomes with time-to-event analysis without saying so explicitly.

Step 6 — Define endpoints and outcome ascertainment

Use references/endpoint-definition-framework.md.

State:

• primary endpoint
• key secondary endpoints
• endpoint definition source
• ascertainment mechanism
• endpoint timing
• whether the endpoint is binary, time-to-event, recurrent, longitudinal, or competing-risk structured

Do not define vague endpoints such as “better prognosis” without an operational definition.

Step 7 — Build the variable collection framework

Use references/variable-collection-taxonomy.md.

Organize variables into clear classes such as:

• exposure / predictor of interest
• baseline demographics
• disease severity and stage variables
• comorbidities
• treatment variables
• laboratory / imaging / pathology variables
• confounders
• effect modifiers
• follow-up variables
• endpoint adjudication variables

Distinguish baseline from post-baseline variables.

Step 8 — Define the main statistical analysis line

Use references/analysis-line-framework.md.

State:

• the primary analysis estimand or main comparison concept
• the primary statistical model family
• key adjustment strategy
• subgroup / interaction logic
• sensitivity analyses
• missing-data handling concept
• whether the design supports prediction modeling, association estimation, or treatment-effect estimation

Do not include every possible analysis. Lead with one coherent main line.

Step 9 — Audit bias, validity, and interpretation limits

Use references/bias-and-validity-review-rules.md.

Review threats such as:

• immortal time bias
• selection bias
• confounding by indication
• misclassification
• measurement heterogeneity
• informative censoring
• missing covariates
• limited event counts
• center effects
• overinterpretation of association as causation

Step 10 — Check feasibility and data quality realism

Use references/feasibility-and-data-quality-rules.md.

State clearly:

• what data elements are likely available
• what may be obtainable with extra effort
• what should be treated as unavailable or uncertain
• where outcome ascertainment may be weak
• whether external validation or replication is realistic

Step 11 — Recommend the lead cohort protocol version

Choose the best protocol framing for now.

State:

• the recommended design version
• why it should lead
• what has been intentionally deferred
• what upgrades would strengthen the study later
• whether the protocol is firm or provisional

Mandatory Output Structure

Use the following sectioned structure every time.

A. Study Intent Summary

Provide a concise restatement of the user’s cohort question, dominant objective, and intended evidence type.

B. Why Cohort Design Fits

State whether a cohort design is appropriate, what interpretation level it supports, and what competing design families were considered but not selected.

C. Recommended Cohort Type

State the recommended cohort type, main alternative, and the design trade-off.

D. Source Population, Enrollment Logic, and Time-Zero

Define source population, eligibility, exclusion logic, cohort entry, index date, and baseline window.

E. Follow-up Architecture

Define follow-up start, duration, visit / observation structure, censoring, loss-to-follow-up concept, and competing events if relevant.

F. Endpoint Framework

Define the primary endpoint, key secondary endpoints, ascertainment source, timing, and endpoint structure.

G. Variable Collection Framework

Organize the variable system into required domains. This section should separate core baseline variables, recommended enrichment variables, and optional exploratory variables.

H. Primary Statistical Analysis Line

State the main analysis objective, model family, covariate adjustment logic, sensitivity analyses, and missing-data concept.

I. Bias and Validity Review

List the main internal validity threats, interpretation limits, and the strongest sources of design fragility.

J. Feasibility and Data-Quality Check

State which assumptions depend on real data access, follow-up completeness, endpoint ascertainment, or variable availability.

K. Recommended Protocol Version

Give the lead protocol recommendation and explain why it is the best version to execute now.

L. Critical Assumptions and Next Clarifications

List the assumptions that still require confirmation and the minimum follow-up questions or decisions needed before the protocol becomes execution-ready.

Formatting Expectations

Follow these formatting rules every time:

• Keep the response sectioned exactly as A–L.
• Use concise paragraphs for interpretation sections.
• Use tables where structure comparison improves clarity.
• The following sections should usually use tables unless the input is extremely simple:
  • D. Source Population, Enrollment Logic, and Time-Zero
  • E. Follow-up Architecture
  • F. Endpoint Framework
  • G. Variable Collection Framework
  • H. Primary Statistical Analysis Line
  • J. Feasibility and Data-Quality Check
• In G, separate variables into necessary / recommended / optional.
• In I, explicitly distinguish bias source, why it matters, and design mitigation.
• In J and L, clearly label anything that is assumption-dependent, uncertain, or not yet verified.
• Do not turn the protocol into a manuscript-style narrative.
• Do not bury the primary analysis line under secondary analyses.

Hard Rules

Study-Design Integrity Rules

• Do not recommend a cohort design if the question is fundamentally better served by another design family without stating that clearly.
• Do not blur eligibility criteria, baseline variable definition, and analysis subgroup definition.
• Do not define time-zero vaguely.
• Do not use post-baseline information as if it were baseline without explicitly labeling the risk.
• Do not present associative cohort estimates as if they prove causality.
• Do not recommend multiple competing primary endpoints without naming one true primary endpoint.
• Do not give an endpoint label without an operational definition.
• Do not recommend a model family that mismatches the endpoint structure.
• Do not assume proportional hazards, linearity, exchangeability, or missing-at-random without acknowledging that these are modeling assumptions.

Feasibility and Data Rules

• Do not invent cohort size, event count, follow-up duration, data completeness, or external validation access.
• Do not assume laboratory, imaging, pathology, medication, or biomarker data are available unless the user said so or the output explicitly labels them as assumption-dependent.
• Do not assume prospective follow-up capacity, patient contact, or endpoint adjudication infrastructure.
• Do not pretend that registry or EHR fields are standardized if that has not been confirmed.
• Do not silently rely on unavailable covariates for the primary adjustment strategy.

Literature and Evidence Integrity Rules

• Never fabricate references, PMIDs, DOIs, trial IDs, registry names, event rates, guideline positions, or published precedent.
• Never imply that a cohort design choice is “standard” or “validated” unless that is actually verified.
• Never state that a biomarker, score, variable definition, or endpoint algorithm is clinically established unless confirmed.
• If literature support is not verified, say so explicitly.
• If an effect size, event rate, or expected follow-up completeness is unknown, label it as unknown rather than guessed.

Output Discipline Rules

• Always provide one lead protocol version.
• Always separate necessary, recommended, and optional variables or design components where applicable.
• Always identify the strongest interpretation limit.
• Always surface the assumptions most likely to fail in real data.
• Always keep the protocol compatible with the user’s stated question rather than inflating it into a more ambitious but less executable design.

Interactive Refinement Rule

If the user asks to improve or revise the protocol, preserve the same A–L output structure unless they explicitly request a different format.

When refining:

• keep the original core question stable unless the user changes it
• state what changed in the revised design
• explain why the change improves interpretability, feasibility, or validity
• do not add complexity unless it solves a concrete design problem

Associated Skills

Upstream

• clinical-question-clarifier
• study-objective-refiner
• primary-plan-recommender
• feasibility-aware-study-planner

Adjacent

• translational-study-blueprint
• medical-research-algorithm-matcher
• biomarker-validation-planner

Downstream

• protocol-writer
• statistical-analysis-plan-writer
• case-report-form-variable-planner

What This Skill Should Not Do

This skill should not:

• act as a patient-care recommendation tool
• write informed consent forms, ethics submissions, or grant prose unless explicitly asked in a later workflow
• generate sample-size calculations from fabricated assumptions
• produce literature citations unless they are verified
• design a randomized trial while calling it a cohort study
• collapse the entire study into a biomarker-only workflow without clarifying the cohort backbone
• treat every available variable as analytically necessary

Quality Standard

A high-quality output from this skill should:

• make clear why the chosen cohort structure fits the question
• define a defensible time-zero and follow-up structure
• provide a usable endpoint framework
• separate baseline, follow-up, and endpoint-related variables cleanly
• present one coherent primary statistical analysis line
• expose the main threats to validity and feasibility
• remain useful even if the user has not yet finalized all operational details
• never overstate certainty, causal interpretability, or data availability