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Contributors
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xxiii
LindaFerrari Guy’s and St Thomas’ NHS Foundation Trust, London, UK
Alessandro Fichera Division of Colon and Rectal Surgery, Baylor University
Medical Center, Dallas, TX, USA
Fergal J. Fleming Division of Colorectal Surgery, Department of Surgery,
University of Rochester Medical Center, Rochester, NY, USA
Bhuwan Giri DeWitt Daughtry Family Department of Surgery, University of
Miami Leondard M.Miller School of Medicine, Miami, FL, USA
Jackson Health System, Miami, FL, USA
Paolo Goffredo Division of Colon & Rectal Surgery, University of Minnesota,
Minneapolis, MN, USA
EmreGorgun Department of Colorectal Surgery, Digestive Disease and Surgery
Institute, Cleveland, OH, USA
Ga-ram Han Department of General Surgery, Division of Colon and Rectal
Surgery, Mayo Clinic, Phoenix, AZ, USA
Traci L. Hedrick Chief, Division of General Surgery, Department of Surgery,
University of Virginia Health, Charlottesville, VA, USA
Susanna S. Hill Division of Colon and Rectal Surgery, Department of Surgery,
University of Minnesota School of Medicine, Minneapolis, MN, USA
JenniferHolder-Murray Division of Colon and Rectal Surgery, Department of
Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA, USA
AlexL.Huang Mount Sinai Hospital, New York, NY, USA
E.Huang Department of Surgery, The Ohio State University College of Medicine,
Columbus, OH, USA
RogerD.Hurst Department of Surgery, University of Chicago, Chicago, IL, USA
Alexandra Jones Department of Surgery, University of Louisville,
Louisville, KY, USA
ScottR.Kelley Mayo Clinic, Colon and Rectal Surgery, Rochester, MN, USA
SergeyKhaitov Mount Sinai Hospital, New York, NY, USA
ErinKing-Mullins Colorectal Wellness Center, Fayetteville, GA, USA
ErvinKocjancic Department of Urology, University of Chicago, Chicago, IL, USA
Reconstructive Urology and Trans Health, Chicago, IL, USA
Julia Kohn Division of Colon and Rectal Surgery, University of Minnesota,
Minneapolis, MN, USA
NathanKohrman Keck School of Medicine of USC, Los Angeles, CA, USA
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Contributors
JohnKonen Rush University Medical College, Department of Surgery, Division
of Colon & Rectal Surgery, Chicago, IL, USA
Monika A. Krezalek Department of Surgery, Division of Colon and Rectal
Surgery, NorthShore University Health System, Evanston, IL, USA
SamuelH.Lai University of Colorado Surgery, Aurora, CO, USA
SeanJ.Langenfeld Division of Colon and Rectal Surgery, Department of Surgery,
University of Nebraska Medical Center, Omaha, NE, USA
JonathanLaryea Division of Colon and Rectal Surgery, Department of Surgery,
University of Arkansas for Medical Sciences, Little Rock, AR, USA
JenniferA.Leinicke Omaha, NE, USA
Chih-Yi Liao Section of Hematology/Oncology, Department of Medicine,
University of Chicago, Chicago, IL, USA
Sender Liberman McGill University Health Centre, Colon & Rectal Surgery,
Montreal, QC, Canada
AmyL.Lightner Department of Colorectal Surgery, Digestive Disease Surgical
Institute, Cleveland Clinic, Cleveland, OH, USA
AnthonyLoria Division of Colorectal Surgery, Department of Surgery, University
of Rochester Medical Center, Rochester, NY, USA
Henry J. Lujan, M.D., F.A.C.S., F.A.S.C.R.S. Jackson South Medical Center,
Colon and Rectal Surgery, Miami, FL, USA
VictorMaciel,MD Allegheny General Hospital/St. Vincent Hospital, Colon and
Rectal Surgery, Pittsburgh, PA, USA
KellieMathis Department of Surgery, Mayo Clinic, Rochester, MN, USA
Nicholas P. McKenna Mayo Clinic, Division of Colon and Rectal Surgery,
Rochester, MN, USA
Evangelos Messaris, MD, PhD, MBA Division of Colon and Rectal Surgery,
Department of Surgery, Beth Israel Deaconess Medical Center, Harvard Medical
School, Boston, MA, USA
MaxwellD.Mirande Mayo Clinic, General Surgery, Rochester, MN, USA
Nitin Mishra Department of Colon and Rectal Surgery, Mayo Clinic,
Phoenix, AZ, USA
YusukeMiyatani Inammatory Bowel Disease Center, The University of Chicago
Medicine, Chicago, IL, USA
MatthewG.Mutch Washington University St. Louis, Colon and Rectal Surgery,
St. Louis, MO, USA
Contributors
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Valentine N. Nfonsam LSU Health Department of Surgery, Louisiana State
University, New Orleans, LA, USA
Cory Nonnemacher Atrium Health Navicent, Department of General Surgery,
Macon, GA, USA
MeganObi Department of General Surgery, Digestive Disease Surgical Institute,
Cleveland Clinic, Cleveland, OH, USA
KingaS.Olortegui Section of Colon & Rectal Surgery, Department of Surgery,
UChicago Medicine, Chicago, IL, USA
ArshaOstowari Department of Surgery, University of California, Orange, CA, USA
IanM.Paquette Chief of the Division of Colon and Rectal Surgery, University of
Cincinnati College of Medicine, Cincinnati, OH, USA
Nell Maloney Patel Rutgers Robert Wood Johnson Medical School, Colon and
Rectal Surgery, Westeld, NJ, USA
Terrah J. Paul Olson Division of Colorectal Surgery, Department of Surgery,
Emory University, Atlanta, GA, USA
KaylaPolcari University of Chicago, Chicago, IL, USA
Vitaliy Poylin Division of Gastrointestinal Surgery Northwestern Medicine,
Feinberg School of Medicine, Chicago, IL, USA
Northwestern University Feinberg School of Medicine, Northwestern Medical
Group, Chicago, IL, USA
Felipe F. Quezada-Diaz Colorectal Unit, Department of Surgery, Complejo
Asistencial Doctor Sótero del Río, Santiago, RM, Chile
OmerRaheem Department of Urology, University of Chicago, Chicago, IL, USA
Shahrose Rahman, MD Department of Surgery, Oregon Health & Science
University, Portland, OR, USA
Ray Ramirez Rutgers Robert Wood Johnson Medical School, Surgery, New
Brunswick, NJ, USA
TobiJ.Reidy Indiana Colon and Rectal Specialists, Indianapolis, IN, USA
Jeffrey L. Roberson Department of Surgery, Hospital of the University of
Pennsylvania, Philadelphia, PA, USA
GustavoA.Rubio Jackson Health System, Miami, FL, USA
Atsushi Sakuraba RUSH Center for Crohn’s and Colitis, RUSH University
Medical Center, Chicago, USA
Nicole M. Saur Division of Colon and Rectal Surgery, Department of Surgery,
Hospital of the University of Pennsylvania, Philadelphia, PA, USA
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Contributors
Cimarron E. Sharon Department of Surgery, University of Pennsylvania,
Perelman School of Medicine, Philadelphia, PA, USA
BenjaminD.Shogan University of Chicago, Chicago, IL, USA
Hillary Simon Division of Colon and Rectal Surgery, Department of Surgery,
University of Louisville, Louisville, KY, USA
BradfordSklow Cleveland Clinic Florida, Department of Colorectal Surgery, Port
St. Lucie, FL, USA
J. Joshua Smith Colorectal Service, Department of Surgery, Memorial Sloan
Kettering Cancer Center, New York, NY, USA
RadhikaK.Smith Washington University St. Louis, St. Louis, MO, USA
Ernie Soto Division of Colon and Rectal Surgery, Department of Surgery,
University of Arkansas for Medical Sciences, Little Rock, AR, USA
MelindaE.Stack Colon and Rectal Surgery Associates, Minneapolis, MN, USA
David B. Stewart Southern Illinois University School of Medicine, SIU
Department of Surgery, Springeld, IL, USA
Patricia Sylla Department of Colon and Rectal Surgery, Mount Sinai Hospital,
New York, NY, USA
JosephTerlizzi Mount Sinai School of Medicine, Surgery, New York, NY, USA
Vassiliki Liana Tsikitis, MD, MBA Division of Gastrointestinal and General
Surgery, School of Medicine, Oregon Health & Science University, Portland, OR, USA
MartinUwah Department of Colon and Rectal Surgery, University of Chicago,
Chicago, IL, USA
MichaelA.Valente University of Arizona, Surgical Oncology, Tucson, AZ, USA
JonD.Vogel University of Colorado Surgery, Aurora, CO, USA
SarahA.Vogler Cleveland Clinic Florida, Martin Health, Port St Lucie, FL, USA
ThomasM.Ward Section of Colon and Rectal Surgery, Division of General and
Gastrointestinal Surgery, Department of Surgery, Massachusetts General Hospital,
Boston, MA, USA
Martin R. Weiser Stuart Quan Chair in Colorectal Surgery, Memorial Sloan
Kettering Cancer Center, New York, NY, USA
Weill Cornell Medical College, New York City, NY, USA
MaggieL.Westfal Washington University St. Louis, Colon and Rectal Surgery,
St. Louis, MO, USA
Matthew Z. Wilson Dartmouth Hitchcock Medical Center, Geisel School of
Medicine at Dartmouth, Division of Colon and Rectal Surgery, Lebanon, NH, USA
Contributors
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Zhaomin Xu Division of Colorectal Surgery, University of Rochester,
Rochester, NY, USA
Sumeyye Yilmaz Department of Colorectal Surgery, Digestive Disease and
Surgery Institute, Cleveland, OH, USA
AllenT.Yu Mount Sinai Hospital, New York, NY, USA
Karen Zaghiyan Division of Colorectal Surgery, Cedars-Sinai Medical Center,
Los Angeles, CA, USA
Evaluating Evidence
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ZhaominXu andBradfordSklow
Evaluating Evidence
Evidence-based medicine (EBM) is an approach to clinical decision-making that
emphasizes the use of the best available evidence to guide clinical practice. The
term was rst coined by Gordon Guyatt from McMaster University in Canada in the
1990s. [1] EBM involves critically evaluating evidence to determine validity, relevance, and applicability to particular clinical situations.
As a starting point, there must rst be a clinical question that is well dened and
therefore answerable. A poorly formulated question results in wasted time and
resources evaluating irrelevant evidence and sources. When considering how to formulate a good clinical question, rst we must dene the patient population we are
interested in. Then, there has to be an exposure or action, which may include a
comparison control. And nally, we must dene a desired outcome. Once the clinical question has been formulated, then we can move forward with identifying relevant sources and evaluating their quality and ability to answer the question.
This chapter will provide an overview of the key steps involved in evaluating
medical evidence, so the reader may formulate their own assessment of the literature and carry these practices forward in their continued education. This chapter is
not meant to serve as an in-depth review of statistics, and there are numerous other
1
Z. Xu
University of Rochester, Division of Colorectal Surgery, Rochester, NY, USA
e-mail: zhaomin_xu@umrc.rochester.edu
B. Sklow (*)
Cleveland Clinic Florida, Department of Colorectal Surgery, Port St. Lucie, FL, USA
e-mail: SKLOWB@ccf.org
© The Author(s), under exclusive license to Springer Nature
Switzerland AG 2023
K. Umanskiy, N. Hyman (eds.), Difcult Decisions in Colorectal Surgery,
Difcult Decisions in Surgery: An Evidence-Based Approach,
https://doi.org/10.1007/978-3-031-42303-1_1
1
2
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Z. Xu and B. Sklow
resources dedicated to statistics that can be referenced if readers have specic questions. For more in depth discussion of many of the topics addressed in this chapter,
a useful reference is “How to Read a Paper: The Basics of Evidence-Based Medicine
and Healthcare,” by Dr. Trisha Greenhalgh [2]. Another useful resource for readers
to reference is a recent set of guides to different statistical methods published by
JAMA Surgery which is easily accessible for those who don’t have a strong statistical background. [3–11]
Assessing Methodology
The study design is critical in determining the strength and quality of the evidence.
A well-designed study will help to minimize bias and confounding factors. Different
study designs have different strengths and weaknesses, and the design should be
chosen based on the research question. The hierarchy of evidence is often used to
rank studies in order of their quality with reviews and meta-analyses based on high
quality randomized controlled trials (RCTs) being generally considered the gold
standard. (Table1.1) This is followed by high-quality RCTs themselves, low quality
RCTs, well-designed case-control and cohort studies, and nally expert opinions at
the bottom of the hierarchy. However, in some instances a large, well-designed
cohort study may be more important than a poorly done meta-analysis or a methodologically questionable RCT.In addition, there are also instances where RCTs may
not be the appropriate study design. [2] For example, if we were interested whether
ctDNA could reliably diagnose a recurrence in a colon cancer patient, the ideal
design would be a cross-sectional study, not a RCT.So, while the traditional hierarchy of evidence we are familiar with is a useful framework to being thinking about
quality of evidence, it is not enough.
Table 1.1 The hierarchy of evidence
Level of
evidence Description
Level I Evidence from a systematic review or meta-analysis of all relevant RCTs or
evidence-based clinical practice guidelines based on systematic reviews of high
quality RCTs.
Level II Evidence from a well-designed RCT.
Level III Evidence obtained from lower quality RCTs or controlled trials without
randomization.
Level IV Evidence from a well-designed case-control or cohort studies
Level V Evidence from systematic reviews of descriptive and qualitative studies
(meta-synthesis).
Level VI Evidence from a single descriptive or qualitative study.
Level VII Evidence from expert opinion.
RCT randomized controlled trial
1 Evaluating Evidence
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There are ve broad questions that should be asked of any paper when assessing
the methodology:
1. Was the study original?
2. What’s the patient population?
3. What are the exposures and outcomes and do they make sense?
4. Was an adequate attempt made to control for bias?
5. Was the study large enough and continued long enough to make the results useful?
Was theStudy Original?
Once we start looking for relevant papers to answer our clinical question, it can suddenly become apparent that there appears to be many papers trying to answer the
same question. While it may seem common sense that a question that has already
been answered shouldn’t be asked again, but the reality is that most papers only tell
us if a hypothesis is incrementally more or less likely than before. It’s rare that a
single paper is enough to change clinical practice. Therefore, the question is not
whether a study is completely novel, but rather does the paper add to the existing
literature in any way.
A paper could add to the existing literature by providing a larger study population
or a longer follow up. Or the paper may be looking at a more dened portion of the
patient population that previous papers did not have the opportunity to explore, such
as a specic age group or minority populations. Perhaps there were methodological
aws with the existing literature that the current paper is trying to correct. And nally,
it could be that for whatever reason, despite there being robust current evidence, there
is still skepticism and therefore an additional study may contribute to a future metaanalysis or review that will contribute to solidifying the literature further.
3
What’s thePatient Population?
The patient population can be tricky. We are frequently faced with a single patient
that generated the clinical question that we are investigating, so no matter how large
and high quality a study may be, there’s the possibility that the study can’t be applied
to our patient because the study population is different from our patient. Therefore,
there are several questions we want to ask ourselves when looking at a study’s
patient population:
1. How were the patients recruited or what was the source of the patient
population?
For example, we may nd a very robust cohort study sourced from an admin-
istrative database like the Medicare dataset. But if our original clinical question
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was in regards to a young patient, the results of this Medicare study may not
apply to our patient no matter how high quality the study is.
The method by which patients are recruited for a study may also lead to
recruitment bias. A common example of this is in survey-based studies where the
sample of patients obtained is skewed in some fashion due to certain populations
being more likely to respond to a particular survey.
2. What were the inclusion and exclusion criteria?
Traditionally, RCTs suffer from limited patient inclusion excluding many
elderly patients, minority populations, and those with poor education or are nonEnglish speakers [12]. While having a very limited population makes for cleaner
and easier studies, it makes results difcult to extrapolate for the general
population. If we are evaluating a cohort study looking at any long-term outcome
of rectal cancer patients, it’s important to know whether any inclusions or exclusions were made based on neoadjuvant or adjuvant therapies. And in this example, some older studies may no longer be relevant despite being robust because
of the differences in how rectal cancer is now managed compared to before.
3. Was the population studied in a different environment?
This question address whether the study population of a paper came from an
environment similar to our patients. If, for example, we practice in a low resource
setting, a robust paper that heralds the newest and best technology to assist with
the endoscopic treatment of large polyps may not be relevant to our practice and
patients. So, while this does not invalidate the paper from a methodological
standpoint and will serve a different population well, it cannot be applied to our
patients
Z. Xu and B. Sklow
What Are theExposures andOutcomes andDo They
Make Sense?
A fundamental question when appraising a paper is what the exposure is and what
is it being compared to, if any comparison is being made. At face value, this may be
quite simple. For example, the authors may have stated in the paper that they compared patients who recorded their ileostomy output to those who did not. However,
this begs the question of how the authors determined whether a patient did or did not
measure their ileostomy output, which inherently require assumptions such as that
patients who were recording, were doing it accurately. Another example would be
in studies that depend on a review of medical records, an assumption is being made
that medical records are accurate and reliable. These assumptions may or may not
be true and could potentially impact the validity of the results. Therefore, it is
important to determine whether the method by which the authors used to gather
their exposure data is reliable. If not, this could skew the results of the study in the
positive or negative.
Similar to exposure, the outcome has to be sensible and measurable. Binary outcomes, such as survival tend to be self-explanatory. However, the difculty with
outcomes such as survival comes down to how the outcome was captured and
1 Evaluating Evidence
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measured and whether this was reliable. We have to assess the methods by which
the authors used to determine whether a patient was still alive and how long did the
authors follow up for to determine the outcome. When evaluating a study that measures an outcome that is less concrete, such as patient-reported outcomes, it is
important to conrm that the outcome measure has been objectively validated and
actually measures what it claims to measure. The development of patient reported
outcome measures should be done in a rigorous and protocol-driven method and can
provide valuable insight into patient perspectives [6].
5
Was anAdequate Attempt Made toControl forBias?
No matter how well designed a study is there can inevitably be error that impacts the
validity of the results. There are two different types of error: random error and systematic error, which is also referred to as bias [13]. Regardless of the study design,
a paper that aims to compare groups should aim for the groups to be as comparable
as possible in order to isolate the effects of the exposure. Random error in a study is
not necessarily a mistake, but a natural part of measurement that result in variability
of the results when the same measurement is repeated multiple times. Random error
impacts precision, which is how reproducible the results of a measurement is when
taken multiple times under the same conditions. It is equally likely to be higher or
lower than the true value and therefore is not typically seen as a large problem. It
can be mitigated through several strategies:
1. Take repeated measurements: For example, if a paper is studying a specic lab
value, there is likely random error associated with the measurement itself, so
perhaps the authors ran the lab multiple times to obtain an average that more
represents the true value.
2. Increase sample size: This is the most common way studies attempt to minimize
random error, and is otherwise referred to as the power of the study. The larger
the sample size, the greater the power. A well-designed prospective study should
have a predetermined power and a power calculation that tells us the number of
patients that are needed to reach that power. When evaluating a study, if the
authors report no statistically signicant difference between an intervention and
control arm and there was no power calculation, the reader needs to examine
whether the study was underpowered [14].
3. Efcient statistical analysis: Estimation of random error is typically carried out
in studies through hypothesis contrast tests (p-values) and condence intervals.
Systemic error, or bias, is directly impacted by study methodology and causes a
skewing of the results that is predictable. Systematic error impacts accuracy, so
unlike random error, results can be very precise and consistent, but it is not around
the true value. There are many different types of bias and they can occur at any stage
of a study. Bias typically falls within three major categories: selection, measurement, and confounding.
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