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Nephrology Dialysis Transplantation 2007 22(9):2459-2468; doi:10.1093/ndt/gfm432
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© The Author [2007]. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Clinical research of kidney diseases 1: researchable questions and valid answers

Pietro Ravani1,2, Patrick S. Parfrey1, Bryan Curtis1 and Brendan J. Barrett1

1Clinical Epidemiology Unit, Faculty of Medicine, Memorial University of Newfoundland, Canada and 2Divisione di Nefrologia, Azienda Istituti Ospitalieri di Cremona, Italy

Correspondence and offprint requests to: Pietro Ravani, MD, Divisione di Nefrologia, Azienda Istituti Ospitalieri di Cremona, Italy, Largo priori 1, Cremona, 26100, Italy. Email: p.ravani@ospedale.cremona.it

The first 150 words of the full text of this article appear below.



   Introduction
 
Clinical epidemiology is the science of human disease investigation. It has a broad scope, ranging from the study of disease occurrence and prognosis to diagnostic and management options.

This series of articles will discuss general and specific issues related to the design, analysis and interpretation of studies using nephrology examples. This first paper introduces general issues of ‘definition’ and ‘measurement’ in clinical studies, along with the related concepts of ‘reliability’ and ‘validity’, or ‘random’ error and ‘systematic’ error (bias).



   Research objectives
 
Much medical research can be simplified as the study of the frequency of an illness and the assessment of some ‘input–output relationship’ in a defined patient population. The purpose is to characterize specific diseases and establish whether an explanatory input variable or exposure (test, predictor or intervention) is related to an output or outcome (gold standard result, response variable or effect).

The goal of research is to estimate these phenomena in . . . [Full Text of this Article]



   Error types
 


   Ideas and structure clinical research
 


   Definitions
 


   Sampling
 
Random sampling
Random assignment to exposure and analysis of trials
Sample size estimation


   Measurement
 
Variable types
Measures of disease frequency and effect
Measurement errors


   Concluding remarks: external and internal validity
 

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This article has been cited by other articles:


Home page
 Nephrol Dial TransplantHome page
P. Ravani, P. Parfrey, S. Murphy, V. Gadag, and B. Barrett
Clinical research of kidney diseases IV: standard regression models
Nephrol. Dial. Transplant., February 1, 2008; 23(2): 475 - 482.
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Home page
 Nephrol Dial TransplantHome page
P. Ravani, P. Parfrey, V. Gadag, F. Malberti, and B. Barrett
Clinical research of kidney diseases III: Principles of regression and modelling
Nephrol. Dial. Transplant., December 1, 2007; 22(12): 3422 - 3430.
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