Medical Statistics : For Beginners

188 Pages·2017·9.258 MB·English

by  Ramakrishna HK (auth.)

Ramakrishna HK
Medical Statistics
For Beginners
123
Medical Statistics
Ramakrishna HK
Medical Statistics
For Beginners
Ramakrishna HK
Subbaiah Institute of Medical Sciences
Shivamogga
Karnataka
India
ISBN 978-981-10-1922-7 ISBN 978-981-10-1923-4 (eBook)
DOI 10.1007/978-981-10-1923-4
Library of Congress Control Number: 2016953631
© Springer Science+Business Media Singapore 2017
T his work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of
the material is concerned, specifi cally the rights of translation, reprinting, reuse of illustrations, recitation,
broadcasting, reproduction on microfi lms or in any other physical way, and transmission or information
storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology
now known or hereafter developed.
T he use of general descriptive names, registered names, trademarks, service marks, etc. in this publication
does not imply, even in the absence of a specifi c statement, that such names are exempt from the relevant
protective laws and regulations and therefore free for general use.
T he publisher, the authors and the editors are safe to assume that the advice and information in this book
are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the
editors give a warranty, express or implied, with respect to the material contained herein or for any errors
or omissions that may have been made.
Printed on acid-free paper
This Springer imprint is published by Springer Nature
The registered company is Springer Science+Business Media Singapore Pte Ltd.
T he registered company address is 152 Beach Road, #22-06/08 Gateway East, Singapore 189721,
Singapore
This book is dedicated
To my parents
Keshavamurthy and Bhagyalakshmi, who taught me
elementary knowledge of how to handle numbers,
To my wife
Dr. Swarnalatha MC, who gave valuable suggestions,
is a constant source of encouragement, and tolerated
my odd working hours,
To my children
Manu and Ajay, who made my life worth living.
Foreword
I feel privileged to write this foreword to the book on Medical Statistics for Beginners
by Dr. H. K. Ramakrishna.
H is introduction to the book, sharing his personal experience and journey as an
author, is a “must read.” Today, the world is really fl at—one’s effort is the only lim-
iting factor. Dr. Ramakrishna has shown what can be done with focused effort.
Where you come from and what your offi cial designation is are completely irrele-
vant, as far as accomplishments are concerned. Dr Ramakrishna deserves high
praise for this work and he should be taken as a “role model” by all surgeons.
Statistics is considered a “dry” subject. But it is essential for us to understand at
least the basics of statistics to function well as surgeons. This book meets this
requirement. The language is simple. The approach is direct and practical. All the
principles are explained in a succinct manner.
One can see from the screenshots that everything is worked out using basic com-
puter tools that are universally available. Several free resources available on the
Internet are introduced. With this, every one of us can do the things that are shown
in the book. The links to statistical calculators that he has himself developed are a
great “value add.”
The chapters on “Designing a Study Clinical Trial or Dissertation,” “Evidence-
Based Medicine” (EBM), and “Writing an Article for Journals” are very apt. After
all, the purpose of statistics is to help us evolve into “scientifi c surgeons.” Every one
of us must endeavor to practice EBM and share our vast experience and add to the
scientifi c knowledge by formally publishing our work.
Finally, I do hope that this book inspires all of us in this country to diligently
document our work and publish more often. We fall woefully short of other coun-
tries—even small South-East Asian countries—in the fi eld of scientifi c publication!
We cannot afford to let the status quo continue.
I wish this book every success. It is a landmark effort in the fi eld of surgical
publication.

Bangalore, India K Lakshman , MS, FRCS
vii
Opin ion
“ Author’s style of writing is easy to read and understand. He gives meaningful
examples to explain each new idea and also explains the methodology which at
times is quite complex and painstaking. Suggestion to use the computer liberally
encourages the reader to learn easy ways of making the complex calculations. The
overview of the Biostatistics is nicely covered.
I believe that this short book may be a nice book for the medical students and
postgraduates to get to know the various statistical terms and methods for them to
use in their academic career.”
Dr. R. D. Prabhu FRCS
ix
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 My Journey from a Rural Surgeon to an Author. . . . . . . . . . . . . . . . . . . . 3
3 Understanding Biostatistics, Probability, and Tests
of Significance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Skewed Distribution Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4 Understanding Basic Statistical Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Measures of Central Tendency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Measures of Dispersion or Spread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Variance and Standard Deviation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Confi dence Interval and Confi dence Level . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Errors Type 1 and Type 2 (Alpha and Beta, Respectively) . . . . . . . . . . . . . . 31
Factors Increasing Type II Error (False Negativity) . . . . . . . . . . . . . . . . . 32
Conditional Probability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Independence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Normal or Gaussian Distribution and Skewed Distribution . . . . . . . . . . . 33
5 Tests of Significance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Chi-Square Test or Simply Chi Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Fisher’s Exact Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Formula for Fisher’s Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
! Is the Symbol for Factorial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Student’s T Test or Gosset’s Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
One- and Two-Tailed Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Paired T Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
ANOVA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Which Test to Use? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Mann–Whitney–Wilcoxon (MWW) Test . . . . . . . . . . . . . . . . . . . . . . . . . 54
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
6 Other Commonly Used Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
ANalysis Of Variance (ANOVA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Rank Test: Wilcoxon Signed-Rank Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
xi
xii Contents
Risk and Risk Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Odds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Odds Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Relative Risk Reduction (RRR), Absolute Risk Reduction (ARR),
and Number Needed to Treat (NNT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Correlation: Relation Between Two Factors . . . . . . . . . . . . . . . . . . . . . . . . . 71
Positive Correlation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Negative Correlation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Correlation Coeffi cient ( r ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Regression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Linear Regression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Other Types of Regressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Logistic Regression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Multiple Regression: To Predict an Outcome . . . . . . . . . . . . . . . . . . . . . . 76
The Poisson Regression (Distribution) . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Cox Regression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Survival Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Kaplan–Meier Estimator or Survival Graph . . . . . . . . . . . . . . . . . . . . . . . 79
Multivariate Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Power of a Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
7 Designing a Study/Clinical Trial/Dissertation, Etc. . . . . . . . . . . . . . . . . . 85
General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Concerns While Designing a Trial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Negative Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Teamwork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Phases of Trials: Applies to New Drugs . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Some Commonly Used Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Parallel Studies and Crossover Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Planning and Pilot Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Sample Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Pilot Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Collection and Compilation of Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Types of Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Data Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Bias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Sampling Errors and Nonsampling Errors . . . . . . . . . . . . . . . . . . . . . . . 102
Data Analysis and Inference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Presentation of Data and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
Bar Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Pie Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Line Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
Contents xiii
Area Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Doughnut Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Histogram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Difference Between Histogram and Bar Chart . . . . . . . . . . . . . . . . . . . . 120
Clinical Audit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Clinical Audit Versus Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Clinical Audit Is an Ongoing Process . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
Problems with Audit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
8 Writing an Article for Journals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
Clear Message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
Type of the Articles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
Quality Indicators of a Journal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
Indexing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
Impact Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
Uniform Requirement for Manuscript Submission . . . . . . . . . . . . . . . . . 133
What Happens After Submission? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
Common Reasons for Rejection of Article or Article Sent Back
for Changes (Problems in the Article) . . . . . . . . . . . . . . . . . . . . . . . . . . 143
Best Chance of Acceptance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
Plagiarism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
Peer Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
Copyright . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
Literature Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
Scholarly Databases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
Limitations and Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
Open-Access Journals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
Publish or Perish? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
9 Evidence-Based Medicine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
What Is EBM? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
Why Do We Need EBM? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
How? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
The Five-Step Approach to EBM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
Benefi ts of EBM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
Limitations of EBM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
10 Model Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
Postoperative Management Protocol to Be Followed . . . . . . . . . . . . . . . . . 168
Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
Paper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179