Does it all make sense?
This book is not an introduction to medical statistics, study design, epidemiology, systematic reviews, evidence‐based medicine, or critical appraisal, although we inevitably touch on all of these things (and more). Even so, if you are not already well versed in some of these fields, you should know a lot more by the time you get to the end.
We have concentrated on improving our readers’ understanding of quantitative research papers, and while qualitative papers contain several important elements which we have not been able to cover here, there are many other areas, particularly at the beginning and ends of papers, which readers of qualitative papers will find relevant to their needs.
Primarily, this book should be of interest to the following individuals:
Clinicians currently practising. This would include GPs, doctors in hospitals, in the community and in public health, nurses, midwives, health visitors, health educators and promoters, physiotherapists, dietitians, chiropodists, speech therapists, radiographers, pharmacists, and other clinically‐related specialists;
Clinicians of all types engaged in research activities: as part of their training; as a condition of their clinical duties; for postgraduate studies and courses; or for professional qualifications.
Those involved with the education and training of health professionals in colleges of health, in universities, and in in‐house training and research departments.
College, undergraduate, and postgraduate students in all medical and clinical disciplines which involve any element of research methods, medical statistics, epidemiology, critical appraisal, clinical effectiveness, evidence‐based medicine, and the like.
In addition, this book should appeal to individuals who although are not themselves clinicians but nonetheless find themselves in a clinical setting, and need some understanding of what the published clinical research in their area means. These people would include:
Clinical auditors and quality assessors
Clinical managers
Service managers, administrators, and planners
Those working in health authorities and in local government social and health departments
Purchasers of health provision.
People not actually employed in a clinical arena but who nonetheless have a professional or personal interest in the medical literature; for example, members of self‐help and support groups (e.g. migraine, stroke, diabetes, Alzheimer's, etc.); medical journalists; research‐fund‐providers; the educated, interested, lay public.
We have structured the contents of the book into a series of units whose sequence mirrors that of papers in most of the better‐quality journals. Thus we start with the preliminaries (title, authors, institution, journal type and status, and so on) and end with the epilogue (discussion, conclusions, and clinical implications). Throughout the book we have used a wide variety of extracts from recently published papers to illuminate our textual comments. In these we have focussed largely, but not solely, on examples of good practice in the hope that this will provide readers with some ‘how it should be done’ benchmarks. Any errors remain, of course, our own.
David Bowers, Allan House, and David Owens
Leeds, 2000
Preface to the Second Edition
We received a great many favourable comments from those who used the first edition of this book – for which many thanks. Why then a second edition? The reason is the usual one in these circumstances – we think we can make the book even better. When we set out to write the first edition we had a good idea of what we wanted to include, but inevitably there was some jostling for the available space. In the end some things that we might have included had to be left on the cutting room floor. With this second edition we have now been able to include most of that excluded material. We have also taken the opportunity to respond to some helpful suggestions from readers. In addition to these changes we have now added a considerable amount of completely new material.
Thus this second edition includes a new chapter on measurement scales, and new or significantly expanded sections on the following: ethical considerations; abstracts; consent to randomization into trials; pragmatic and explanatory trials; intention‐to‐treat analysis; elements of probability; data transformation; non‐parametric tests; and systematic review, among others.
Moreover, there is a lot of new material in the chapters on regression – including more on variable selection and model building, and on Cox regression. A good deal of the material in the middle chapters of the book has been re‐arranged and improved to make for a better and more lucid flow (the treatment of dummy variables has been brought forward a chapter, for example).
We have all taken the opportunity to update many of the extracts from clinical papers which we use to illustrate the various ideas and procedures we describe, and also to revise much of the text in the book to improve clarity and understanding. We remain more than willing to receive any constructive comments and suggestions from readers. Otherwise we are confident that this is now an even better book than the original.
SOME NOTES ON STATISTICAL SOFTWARE
There are several statistical packages, of varying levels of sophistication and complexity, which can be used to analyse clinical data. Among the most widely used are the following:
CIA (Confidence Interval Analysis)
EPI‐Info
Minitab
SPSS (the Statistics Package for the Social Sciences)
STATA
S‐PLUS
In our opinion Minitab is the simplest and friendliest statistics package for the general user. SPSS is not quite as easy to use but handles cross‐tabulation of two variables rather better and has a wider range of the more sophisticated types of analyses. The choice of types of analysis and their outputs are perhaps easier to understand in Minitab than in SPSS. Each application has, of course, its limitations. To the best of our knowledge, Minitab does not do the McNemar test, nor does it have a clinically‐based survival analysis programme, nor allow for a direct calculation of Spearman's correlation coefficient (the data needs first to be ranked). On the other hand, SPSS does not allow a chi‐squared test to be done directly on a contingency table in the columns of the data sheet, nor does it provide confidence intervals for the difference between two proportions, or with the Mann–Whitney or Wilcoxon tests, all of which Minitab does. But as we have said, SPSS has a wider range of applications.
CIA, as its name implies, only does confidence interval calculations (but in this respect is very useful). EPI‐Info is a combination database and epidemiological tool, which originates from the Centre for Disease Control (CDC) in the USA. It has the advantage of being free (it can be downloaded from the internet along with a user's manual).
Most professional clinical statisticians will probably use either STATA or S‐PLUS; both more powerful and versatile than either Minitab or SPSS (but rather less easy to use).
We
