What is it? Why is it important?

The aim of a Sample Size Calculation (SSC) is to determine the minimum number of participants needed to address a study question. To calculate and decide on an applicable sample size, two main statistical frameworks are used:

 

  1. The hypothesis testing: the primary outcome / endpoint is assessed with a statistical test (e.g. the difference between an intervention and control group). In a hypothesis testing framework, two competing hypotheses are formulated, the:
    • Null hypothesis (H0) corresponds to the hypothetical claim that the treatment effect does not exist (e.g. no effect)
    • Alternative hypothesis (Ha) - contradicts the null hypothesis (e.g.claims the existence of a treatment effect)

 

  1. The Precision-based approach: The aim is to estimate a quantity with a certain accuracy. For example, the frequency of patients with a cardiac event (e.g. with a precision of +/- 2.5%), in other words with a certain width of the Confidence Interval (CI)

More

The goal of hypothesis testing is to quantify the extent to which the null hypothesis is plausible in light of the data.

The most widely accepted way of quantifying evidence against the null hypothesis is to use the p-value. Given that the null hypothesis is true, the p-value is defined as the probability of obtaining a result equal to or more extreme than what was observed. The smaller the p-value, the stronger the evidence against the null hypothesis.

For example, a p-value of 0.001 means that if the null hypothesis was true, then we have a chance of 1 out of 1000 to observe a result equal or more extreme as the current one, i.e., the null hypothesis is not compatible with the observed data.

What do I need to do?

As a SP-INV:

  • Consult a statistician who can support you in the calculation of your study sample size
  • Provide him/her accurate and reliable information’s (see added information under More)
  • Ensure that the planned recruitment-target for study participants is realistic and achievable

 

As a SP-INV, you need to understand the importance of a proper sample size calculation. Keep in mind that a smaller sample size — whether due to an underestimation during study planning, or the premature termination of participant recruitment — will reduce the statistical power of the study. This may compromise its ability to answer the research question (i.e., a potential treatment effect may be missed).

More

For a sample size calculation the following information should be provided to the statistician:

  • The objective of your study, which will determine the statistical framework of your study
  • The primary outcome/endpoint, including variable type (e.g. continuous, categorical, binary, count)
  • The variability for Δ (σ): a greater measurement variability makes it harder to detect a true effect from noise, which requires an increase in the study`s sample size.

 

In a hypothesis testing framework, the key ingredients to calculate the sample size of a study are:

  • The (minimal) clinically relevant treatment effect (Δ): the smallest difference of the primary outcome that clinicians and patients would care about, and the effect size we want to minimally detect in a study
  • The Type I error (α): also known as a false positive. It represents a situation where the researcher concludes that there is a significant effect when, in reality, there is no such effect Type I error is classically set at 5%.
  •  The Power (1 - β) : it is the probability of correctly rejecting the null hypothesis (e.g. a cholesterol-lowering drug has an effect on cholesterol levels). It is classically set at 80 or 90%.

Where can I get help?

Your local Research Support Centre↧ can assist you with experienced staff regarding this topic

  • Basel, Departement Klinische Forschung (DKF), dkf.unibas.ch

  • Lugano, Clinical Trials Unit (CTU-EOC), ctueoc.ch

  • Bern, Department of Clinical Research (DCR), dcr.unibe.ch

  • Geneva, Clinical Research Center (CRC), crc.hug.ch

  • Lausanne, Clinical Research Center (CRC), chuv.ch

  • St. Gallen, Clinical Trials Unit (CTU), h-och.ch

  • Zürich, Clinical Trials Center (CTC), usz.ch

SCTO Research Tools & Resources

External Links

References

ICH GCP E6(R3) Guideline – see in particular:

  • Essential records table: documentation statistical consideration
  • 3.11.4.5.4 Monitoring of clinical trials
  • 3.16.2 b Statistical programming
  • B.10.2 Statistical consideration

ICH Topic E9 statistical Principles for Clinical Trials – see in particular

  • 3.5 Sample size
  • 4.4 Sample size adjustment

ICH Topic E8(R1) General considerations for clinical studies - see in particular

  • 5.1 Study population
  • 5.6 Statistical analysis

Swiss Law

ClinO – see in particular article

  • Art. 2b Definition of intervention

ClinO-MD – see in particular article

  • Art. 2a Definition of clinical intervention
  • Art. 2a Definition of performance study

HRO – see in particular article

  • Art. 3a Definition of research
Abbreviations
  • ClinO – Clinical Trials Ordinance
  • ClinO-MD – Ordinance on Clinical Trials of Medical Devices
  • CI – Confidence Interval
  • ClinO – Clinical Trials Ordinance
  • HRO – Human Research Ordinance
  • ICH – International Council for Harmonisation
  • ICH-GCP – International Council for Harmonisation - Good Clinical Practice
  • MI – Myocardial Infarction
  • SCTO – Swiss Clinical Trial Organisation
  • SD – Standard Deviation
  • SP-INV – Sponsor Investigator
  • SSC – Sample Size Calculation
Development ↦ Statistic Methodology ↦ Study Design ↦ Sample Size Calculation
Study
Basic

Provides some background knowledge and basic definitions

Basic Protocol
  1. Research and Ethics
    1. Principles
    2. Ethical Dilemma
  2. Study Protocol
    1. Aim
Basic Management
  1. Study Management
    1. Definition
Basic Ethics and Laws
  1. Principles of Ethics Research
    1. Declaration of Helsinki
    2. Declaration of Taipei
  2. Authorities
    1. Ethics Committee
    2. Swissmedic
    3. Federal Office of Public Health
    4. International
  3. Swiss Law
    1. Human Research Act
    2. Transplantation Act
    3. Stem Cell Research Act
    4. Data Protection Act
  4. Clinical Trials Ordinance
    1. Aim
    2. Medicinal Product Studies
    3. Other Clinical Studies
    4. Transplantation
    5. Transplant Products
    6. Gene Therapy, GMO, Pathogenic
    7. Ionising Radiation
  5. Clinical Trials with Medical Device Ordinance
    1. Aim
    2. Medical Device Studies
    3. In Vitro Diagnostic Medical Device Studies
    4. Ionising Radiation
  6. Medical Device Ordinance
    1. Aim
    2. Notified Bodies
  7. Human Research Ordinance
    1. Aim
    2. Projects with Data and Biological Material
    3. Further-use of Data and Biological Material
    4. Further-use and Informed Consent
    5. Deceased Persons Embryos and Foetuses
  8. Organisation Ordinance
    1. Aim
  9. Human Research Coordination Portal
    1. Human Research in Switzerland
  10. Submission Portal
    1. Ethics Portal BASEC
    2. Swissmedic eGov Portal
  11. Guidelines
    1. Good Clinical Practice E6
    2. ISO 14155
    3. ISO 20916
Basic Documents
  1. Document Management
    1. Purpose
    2. In Studies
    3. Document Identification
    4. Document Filing
  2. Standard Operating Procedures
    1. Purpose
  3. Working Instructions
    1. Purpose
  4. Logs
    1. Purpose
  5. Essential Documents or Records
    1. Requirement
  6. Certified Copies
    1. Procedures
Basic Safety
  1. Safety Laws
    1. Aim
  2. Safety Terminology
    1. Overview
  3. Safety Data
    1. Product Development
    2. Pre-Clinical Studies
    3. In Clinical Studies
  4. Safety Information
    1. Investigator Brochure
  5. Safety Vigilance
    1. Pharmacovigilance
    2. Materiovigilance
Basic Data Management
  1. Data Management
    1. In Studies
  2. Study Database
    1. Clinical Data Management System
    2. Study Data
    3. Raw Data
    4. Metadata
  3. Regulatory Requirements
    1. Swiss Law
    2. EU Regulation
Basic Statistic Methodology
  1. Statistics
    1. Definition
    2. Statistician Role
    3. Statistical Software
  2. Research Question
    1. Definition
    2. The Population
    3. Intervention and Control Groups
    4. Placebo and Comparator
    5. Study Primary Outcome / Endpoint
    6. Outcome Endpoint Description
  3. Study Variables
    1. Definition
    2. Predictor Variable
    3. Confounding Variable
Basic Quality and Risk
  1. Risk-Based Approach to Quality
    1. Definition
    2. Risk Identification
    3. Risk Evaluation and Prioritisation
    4. Risk Evaluation Matrix
    5. Risk Control Measures
    6. Risk Assessment Form
  2. Quality Requirements
    1. Quality by Design
    2. Critical to Quality
    3. Risk-Based Quality Management System
  3. Quality Responsibilities
    1. Sponsor-Investigator
    2. Site-Investigator
    3. Study Staff
Basic Monitoring
Basic Drug or Device
  1. Therapeutic Products
    1. Definition
    2. Generic Products
    3. Complementary and Herbal Medicine
    4. Orphan Drugs
    5. Product Development
    6. Good Manufacturing Practice
    7. Market Surveillance
    8. In Studies
  2. Medicinal Product
    1. Definition
    2. Market Authorization
    3. Manufacturing and Distribution
  3. Medical Device
    1. Definition
    2. Conformity Assessment
    3. Manufacture Responsibility
  4. In Vitro Diagnostic Device
    1. Definition
Basic Biobanking
  1. Definition
    1. Biobank
    2. Biological Material
    3. Specimen / Sample
    4. Pre-Analytical Phase
    5. Data Coding / Anonymisation
    6. Incidental Findings
  2. Donor
    1. In Research
  3. The Swiss Law
    1. Human Research Ordinance
    2. Research with Biological Material
    3. Further Use of Biological Material
    4. Further Use and Informed Consent
  4. Ethics Principles
    1. Declaration of Taipei
  5. Biobanking Standards
    1. ISO Biobanking
  6. Swiss Biobanking Platform
    1. Aim
    2. Services
    3. Quality Labels
Concept

Starts with a study idea

Ends after having assessed and evaluated study feasibility

Concept Protocol
  1. Research Question
    1. Feasibility
    2. Patient and Public Involvement
Concept Management
  1. Study Idea
    1. Feasibility
    2. Implementation
    3. Design
  2. Resources
    1. Study Staff
    2. Infrastructure
    3. Storage
    4. Partners
    5. Budget
Concept Ethics and Laws
  1. Research Aim
    1. Advancing Science
    2. Marketing Products
  2. Research Integrity
    1. Principles
    2. Conflict of Interest
    3. Participant Protection
  3. Ethics and Regulatory Requirements
    1. Ethics Requirements
    2. Laws and Guidelines
    3. Institution Requirements
    4. Study Compliance
  4. Ethics and Regulatory Advice
    1. Ethics Clarification
    2. Swissmedic Scientific Advice
    3. Swissmedic Pre-Submission
Concept Documents
  1. Required Documents
    1. Protocol and Synopsis
    2. Investigator's Brochure
Concept Safety
  1. Safety in Studies
    1. Risk-Benefit Ratio
    2. Participant Risk-Benefit
  2. Study Risk Categorisation
    1. Procedures
    2. Risk Categories
Concept Data Management
  1. Stakeholders
    1. Sponsor-Investigator
    2. Data Manager
    3. Statistician
    4. Site-Investigator
    5. Monitor
  2. Clinical Data Mgmt. System
    1. Selection
    2. Computerised System Validation
  3. Server Management
    1. Data Storage
    2. Back-Up and Recovery
Concept Statistic Methodology
  1. Study Feasibility
    1. Research Question
Concept Quality and Risk
  1. Study Feasibility
    1. Aim
    2. Feasibility Questionnaire
    3. Study Team Feedback
    4. Patient and Public Involvement
Concept Monitoring
  1. Monitoring
    1. Aim
    2. Study Requirement
    3. Site Qualification
Concept Drug or Device
Concept Biobanking
  1. Biobanking in Studies
    1. Requirement
    2. Quality of Biological Material
  2. Management of a Biobank
    1. Biobank Goverance
    2. Biobank Regulation
    3. Material Transfer Agreement
Development

Starts with confidence that the study is feasible

Ends after having received ethics and regulatory approval

Development Protocol
  1. Formal Structure
    1. Requirements
    2. Protocol Template
  2. Writing the Protocol
    1. Content
    2. Responsibilities
    3. Patient and Public Involvement
  3. Study Participants
    1. Participant Risks and Benefits
    2. Participant Right
Development Management
  1. Responsibilities
    1. Sponsor-Investigator
    2. Site-Investigator
    3. Project Leader
    4. Staff Qualification and Training
    5. Good Clinical Practice Training
  2. Study Quality
    1. Implementation
  3. Study Safety
    1. Requirement
  4. Study Management
    1. Oversight
    2. Tracking
    3. Infratructure and Maintenance
    4. Multicentre Studies
    5. Insurance
    6. Outsourced Services
    7. Contract
    8. Budget
    9. Patient and Public Involvement
  5. Study Documents
    1. Protocol
    2. Participant Information Sheet
    3. Informed Consent Form
    4. General Consent
    5. Essential Documents
    6. Source Data
  6. Informed Consent Process
    1. Procedures
    2. Exemption from written Consent
  7. Study Approval
    1. Ethics Committee
    2. Swissmedic
    3. Fed. Off. Public Health
  8. Biobanking
    1. Management
Development Ethics and Laws
  1. Ethics Application
    1. Submission
    2. Application Dossier
    3. Approval
  2. Swissmedic Application
    1. Submission
    2. Application Dossier
    3. Early Clarification Meeting
    4. Late Clarification Meeting
    5. Approval Medicinal Products
    6. Approval Medical Device
  3. Federal Office of Public Health Application
    1. Submission
    2. Approval
Development Documents
  1. Required Documents
    1. Study Protocol
    2. Participant Information
    3. Insurance and Contract
    4. Study Documents
    5. Document Submission
Development Safety
  1. Safety Documentation
    1. The Protocol
    2. Study Documents
    3. Data Protection
Development Data Management
  1. Database Development
    1. Variables
    2. Specification
    3. Case Report Form
    4. Calculated Fields
    5. Data Coding and Anonymisation
    6. Data Confidentiality
  2. Data Quality
    1. Requirement
    2. Quality Assurance
    3. Data Management Plan
    4. Data Monitoring
    5. Data Transfer Agreement
  3. Database Lock
    1. Procedures
Development Statistic Methodology
  1. Statistics in the Protocol
    1. The Hypothesis
    2. Data-Analysis-Set
    3. Intercurrent Events
    4. Estimands
    5. Primary and Secondary Analysis
    6. Analysis Method
    7. Missing Data
    8. Study Termination Criteria
  2. Study Design
    1. Definition
    2. Sample Size Calculation
    3. Randomization
    4. Study Blinding
    5. Interim Analysis
  3. Analysis Plan
    1. Procedures
  4. Quality Control
    1. Procedures
Development Quality and Risk
  1. Quality Processes
    1. Development
  2. Quality and Risk Management
    1. Procedures
    2. Risk Strategy
  3. Quality Assurance
    1. Aim
    2. Audit
  4. Quality Control
    1. Aim
    2. Non-Compliance
Development Monitoring
  1. Monitoring Strategy
    1. Aim
    2. Risk-Based Monitoring
    3. On-Site Monitoring
    4. Central Data Monitoring
    5. Off-Site Monitoring
    6. Monitoring Plan
Development Drug or Device
Development Biobanking
  1. Biobank Set-Up
    1. Biobank Database
    2. Facilities and Materials
    3. Collection / Storage Containers
    4. Storage Equipment
    5. Equipment Maintenance
    6. Freezer Emergency Plan
  2. Donor Consent
    1. In Clinical Studies
    2. In Research Projects
    3. For Further Use
    4. Communication
  3. Handling of Biological Material
    1. Sample Workflow
    2. Sample Collection
    3. Sample Transport
    4. Sample Reception
    5. Sample Processing
    6. Sample Storage
    7. Sample Distribution
    8. Sample Analysis
  4. Documentation
    1. Forms and Logs
    2. Non-Conformities
  5. Safety
    1. Risk-Based Approach
    2. Donors
    3. Biobanking Staff
  6. Quality Control
    1. Quality Control Indicators
    2. Data Monitoring
    3. Method Validation
Set-Up

Starts with ethics and regulatory approval

Ends after successful study initiation

Set-Up Protocol
  1. Protocol Training
    1. Requirements
Set-Up Management
  1. Registration
    1. Research Transparency
  2. Study Training
    1. Staff Delegation
  3. Document Management
    1. Requirements
  4. Investigational Product
    1. Definition and Handling
  5. Laboratory
    1. Purpose and Requirement
  6. Study Ready for Conduct
    1. Requirements
Set-Up Ethics and Laws
  1. Study Set-Up
    1. Requirements
Set-Up Documents
  1. Required Documents
    1. Staff Training
    2. Staff Qualification
    3. Master and Site File
Set-Up Safety
  1. Safety Management
    1. Safety Management Plan
    2. Emergency Unblinding
  2. Data Safety Monitoring Committee
    1. Aim
Set-Up Data Management
  1. Database Release
    1. Requirement
    2. Access Rights
    3. Training
Set-Up Statistic Methodology
Set-Up Quality and Risk
Set-Up Monitoring
  1. Site Initation Visit
    1. Aim
    2. Prerequisite
    3. Preparation
    4. Conduct
    5. Report
Set-Up Drug or Device
Set-Up Biobanking
  1. Regulatory Affairs
    1. Requirement
  2. Staff Management
    1. Requirement
  3. Sample Management
    1. Sample Traceability
    2. Packaging and Shipment
  4. Biobanking in Studies
    1. Procedures
Conduct

Starts with participant recruitment

Ends after the last participant has completed the last study visit

Conduct Protocol
  1. Protocol Amendment
    1. Procedures
Conduct Management
  1. Participant Recruitment
    1. Pre-Screening
    2. Screening and Consent
    3. Documentation
  2. Amendment
    1. Protocol
    2. Patient Information
  3. Responsibility and Oversight
    1. Sponsor and Site-Investigator
    2. Drug and Device Accountability
    3. Compliance
    4. Newsletter
  4. Patient and Public Involvement
    1. Participation
Conduct Ethics and Laws
  1. Study Conduct
    1. Compliance and Quality Aspects
    2. Data Protection
  2. Participant Protection
    1. Requirements
    2. Consent of Vulnerable Participants
  3. Amendment
    1. Type
    2. Submission
    3. Approval
  4. Safety
    1. Requirements
  5. Inspections and Audits
    1. Inspection Conduct
    2. Audit Conduct
    3. Audit Certificate
  6. Premature Study Termination
    1. Rationale
    2. ReportingTimelines
Conduct Documents
  1. Required Documents
    1. Oversight Documentation
    2. Patient File
    3. Source Data
    4. Amendment
Conduct Safety
  1. Safety Risk Review
    1. Aim
  2. Safety Assessment
    1. Medicinal Product
    2. Medical Device
    3. Other Clinical Trials
    4. Non-Intervention Research Projects
  3. Safety Reporting
    1. Procedures
    2. Responsibilities
  4. Medicinal Product Safety Reporting
    1. Adverse Event
    2. Serious Adverse Event
    3. (Serious) Adverse Drug Reaction
    4. Suspected Unexpected Serious Adverse Reaction
    5. Advanced Therapies
  5. Medical Device Safety Reporting
    1. Adverse Event / Adverse Device Effect
    2. Serious Adverse Event and Device Effect
    3. Device Deficiency
  6. Non-Interventional Research Safety Reporting
    1. Serious Events
  7. Safety and Protective Measures
    1. Procedures
  8. Annual Safety Report
    1. Procedures
Conduct Data Management
  1. Data Entry
    1. Requirement
    2. Collection
    3. Data Integrity
  2. Data Quality
    1. Responsibility
  3. Amendment
    1. Requirement
    2. Adding Stakeholders
  4. Data Processing
    1. Data Import
    2. Interim Lock
    3. Data Translation
Conduct Statistic Methodology
  1. Interim Analysis
    1. Procedures
Conduct Quality and Risk
  1. Risk Review
    1. Procedures
  2. Deviation Documentation
    1. Note to File
  3. Regulatory Inspections
    1. Conduct
    2. Findings
    3. Corrective and Preventive Actions
Conduct Monitoring
  1. Routine Monitoring Visit
    1. Preparation
    2. Conduct
    3. Findings
    4. Report
    5. Follow-Up
Conduct Drug or Device
Conduct Biobanking
  1. Biobanking Operation
    1. Processes
Completion

Starts with last study visit completed

Ends after study publication and archiving

Completion Protocol
  1. Administrative Tasks
    1. Procedures
Completion Management
  1. Study Closure
    1. Close-Out Visit
    2. Database Lock
    3. Notification of Closure
    4. Lessons Learned
  2. Clinical Study Report
    1. Requirement
  3. Publishing
    1. Study Registries
    2. Scientific Publications
  4. Archiving
    1. Study Records
Completion Ethics and Laws
  1. End of Study Notification
    1. Reporting Timelines
    2. Registry Update
  2. Clinical Study Report
    1. Requirement
  3. Publications
    1. Responsibilities
  4. Inspections and Audits
    1. Procedures
  5. Archiving
    1. Requirements
    2. Duration
Completion Documents
  1. Required Documents
    1. Study Closure
    2. Doument Archiving
    3. Document Destruction
Completion Safety
  1. Clinical Study Report
    1. Procedures
Completion Data Management
  1. Final Database Lock
    1. Procedures
  2. Data Export
    1. Data Formatting
    2. Data Sharing
  3. Clinical Study Report
    1. Requirement
  4. Archiving
    1. Requirement
Completion Statistic Methodology
  1. Data Quality Check
    1. Procedures
  2. Data Preparation
    1. Procedures
  3. Data Analysis and Reporting
    1. Procedures
  4. Publication
    1. Statistician Responsibility
  5. Data Sharing
    1. Data Preparation
Completion Quality and Risk
  1. Clinical Study Report
    1. Quality Aspects
    2. Lessons Learned
Completion Monitoring
  1. Close-Out Visit
    1. Preparation
    2. Conduct
    3. Report
    4. Follow-Up
    5. Archiving
Completion Drug or Device
Completion Biobanking
  1. Leftover Biological Material
    1. For Further-Use
    2. Destruction
  2. Publication
    1. Analytical Results
Current Path (click to copy): Development ↦ Statistic Methodology ↦ Study Design ↦ Sample Size Calculation