BIAS TYPES and ASSESSMENT of BIAS in HEALTH STUDIES

Health studies are the basis of guidelines in healthcare, treatment protocols and health planning. These important studies concerning the human body must also be carefully planned, implemented and reported. The most important problems in evidence-based medicine implementations are the voluntary or involuntary research errors in these research processes. The aim of this study was the assessment of the important bias sources in health studies and the methods used to control these sources of errors. Bias resources can generally be assessed under three titles: Possible sources of bias “Before collecting research data”, “During collecting research data”, “After collecting the research data”. It is thought that this classification will provide a systematic point of view in planning of study, collecting data, analyzing data and reporting the analyzed data. Bias sources can be controlled by tools such as domain based evaluations, checklists, scales. Although the tools prepared by ICMJE (International Committee of Medical Journal Editors) and the EQUATOR Network (Enhancing the QUAlity and Transparency Of Health Research) are used for the research reporting standards; by the principle of transparency, they also contribute to prevention of biases partially. However, some international working groups (such as Cochrane) have not been satisfied with these tools, they have developed various tools to measure bias. Reducing errors in health studies and measuring the amount of errors are important to identify eligible studies that can be used in evidence-based medicine practice. There are various tools to assess bias resources, the use of these existing tools and the development of more useful tools will be beneficial in generation and selection of eligible data