Tips for retrospective studies in clinical medicine

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Tips for Retrospective Studies
Calvin S.H. Ng MD FRCS FCCP
Professor, Thoracic Surgery
The Chinese University of Hong Kong

Areas to cover
• Approvals
• Project design
• Real World
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Institutional Review Board (IRB)
• Committee to approve, monitor & review biomedical and behavioural
research relating to humans.
• Each hospital / university maintains its own
• Often minimum no. of members (5) (include scientist / non-scientist)

Is IRB approval always needed?
• Depends on your intent of the data
• Intent :
• Use to improve processes and operations internally -no
• Improve clinical services to patient care locally at institute – no
• Gauge performance & improve quality of care at your institution-no
• Intent :
• Publish data (even when aggregate de-identified) – yes
• Contribute to general knowledge via poster, meeting, or publication – yes

Minimal Risk - Definition
• Probability and magnitude of harm or discomfort anticipated in the research
are not greater than those ordinarily encountered in daily life or during the
performance of routine physical or psychological examinations or tests.
US Federal Code

Exempt Category
• Education research (about education technique)
• Surveys, interviews, educational tests, public observations (that do not
involve children)
• Studies of public officials
• Analysis of previously-collected , anonymous data
• Public benefit or service program
• Consumer acceptance , taste, and food quality studies

Expedited Categories

Getting through IRB Tips
• Robust rationale / background
• Detailed plan for data analysis (statistics)
• De-identified information only
• Data collection sheet
• Data management plan
Protection of patient
privacy and data

Rationale / Background
• Justification for why you are asking this research question.
• Comprehensive literature search
• Lay it out logically, A+B+C=D
• Lung resection surgery require average xx days hospital stay (data)
• VATS shown to have fewer days hospital stay (data)
• Uniportal VATS may cause less access trauma , but operated through
small incision
• Does Uniportal VATS result in fewer days in hospital ?

Patient Identifiers
• Can not be exempt if any will be recorded
• Name MRN, Insurnce ID#, account #, IP address, vehicle or device identifiers
• Any geographical data ( can localize the patient to a small area – smaller than
state )
• Phone , fax , email
• Biometrics (fingerprint., etc)
• Identifiable images
• Dates relating to an individual
• Birthdate, admission date, discharge date , death date , etc

Deidentification
• Recommend to keep a coded system of patient numbers
• Only study assign code associated with any health data
• Code can not be derived from patient ( no initials, dates, etc .. )
• Easiest is just chronologic numeric assignment

Protocol Review Monitoring Committee (PRMC)
• National Cancer Institute (NCI) requires review all research studies in areas of
diagnosis, therapy, prevention and control of cancer.
• NCI guidelines require a qualified scientific review and monitoring committee
with sufficient size and breadth of expertise to conduct a critical , fair review o
all clinical research protocols comprising the cancer center

IRB versus PRMC review
• Aim of IRB:
• Protect rights of human subjects who participate in research
• Assess the risks and benefits of proposed research
• Minimal risk
• Ensure confidentiality and informed consent
• Aim of PRMC
• Determine scientific validity
• Assure appropriate designed study
• Evaluate feasibility
• Establish their relative priority to the institutional mission
• Monitor all protocols for accrual and progress

Areas to cover
• Approvals
• Project design
• Real World

Research question
• Clinical question to be answered by primary objective
• Appropriate and sufficient rationale
• Data endpoints support primary objective
• Data points are available in retrospective nature
• How recorded? → ease of collection
• Common occurrence vs. rare ?
• Example DVT rates

Secondary Objectives
• The sample size calculation is based on the primary endpoint
• Common error – Avoid overloading the study with too many objectives and
too much data collection
• Interpretation is difficult
• Secondary objectives should help to clarify the primary objective
• Don’t introduce an entirely new research question
• “ Secondary endpoints cannot be validly analyzed if the primary endpoint
does not demonstrate clear significance “

Surrogate Endpoints
• Indicator of effect that is highly correlated with the clinical
outcome of interest
• Rationale: easier , less expensive , sooner, etc
• Must have data or strong plausibility of correlation
• Examples: amount of analgesics taken for pain /pain score
• WCC / CRP as infection

Defining Endpoints
• Very specific upfront
• Plan for exact data, not interpretation of that data
• Example : for development of hepatotoxicity from drug
• Collect : Alk phos , t.bili, AST, ALT, +/- encephalopathy
• Grade 1-4 by NCI CTCAE (version 4.0)

Being more specific
• Example: Determine frequency of chest infection after lung resection surgery
• Define lung resection; sublobar , lobar, wedge ? Technique matters (MITS/ open)?
• Define infection; fever? Elevated WCC? Clinical respiratory deterioration ? CXR show
infective changes
• Need pre-op WCC ? Need pre-op CXR ? ( what if not done pre-op)
• What if only some of the criteria met?
• Simply measure yes/ no to chest infection, or quantify degree of infection?

Finding target population
• Target population:
• Define population clearly,
• Characteristics, location , criteria
• Inclusion / exclusion criteria
• Have a specific reason for each exclusion
• Don’t become so restrictive that it’s biased
• Determine sample size ( use statistician people)
• Missing data
• Lower sample size → loss of power
• Bias → loss of validity

Power Calculations
• Design to have the potential to show statistical significance of the effect size
• Effect Size : a clinically meaningful difference worth detecting
• Must have an estimate of the effect size and relative frequency with which it
occurs
• Background research

Sampling
• Your population: Lung cancer resection patients receiving MITS during 2015
• By diagnosis
• All patients with new diagnosis lung cancer in 2015
• By time period
• All patients admitted to surgical ward in 2015 with diagnosis of lung cancer
• By treatment
• All patients that received MITS during 2015

Sampling
• Unbiased sampling method
• Reverse chronologic
• Random sample within define date range
• Inpatient v. Outpatient
• Changes the level of detail you can get and where from
• Inpatient is simpler , cleaner , but less complete picture.

Areas to cover
• Approvals
• Project design
• Real World

Use of resources & limitations
• Personal / institutional data or databases (US institutions)
• National Registries ( own country / others ), example, SEER, NCDB
• Some are open access
• Aware of:
• limitations of their search capacity / search ability
• their coding & limitations
• What gets and does not get recorded, and granularity of data
• Etc…

• Read papers related to your subject that used that database.
•
• Look at their methods section, analysis section –see what they have to be aware of.
• How can use statistics to remove some of the bias
• Look at their limitations discussion

• Retrospective / latent
bias
• SEER cannot provide
specific code for
GGO-dominant
adenoCA or subtype
of adenoCA
• No data on post-op
adjuvant therapy
etc…

Limitations – at write up
• Do not shoot yourself down
Limitations:
• Acknowledge them
• How you remedial it ( ex:
by stats)
• Limitation may not be very
important in question you
are trying to answer

Summary
• Have others review your project thoroughly
• Be very specific regarding data points
• Allow time for necessary approvals
• Understand the ways patient charts can be identified
• Determine the best way to pull your initial patient list
• Use department resources available to you
• Pick a topic you are interested in.

The Chinese University of Hong Kong
Prince of Wales
Hospital
Thank you

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