The Newcastle-Ottawa Scale (NOS) for Assessing the Quality of Nonrandomised Studies in Meta-Analyses

TLDR

Nonrandomised studies such as case‑control and cohort designs are difficult to conduct, and assessing their quality is essential; the Newcastle‑Ottawa Scale was created by Newcastle and Ottawa universities to address this need. The study aimed to develop an easy, convenient instrument—the Newcastle‑Ottawa Scale—to assess the quality of nonrandomised studies for use in systematic reviews and meta‑analyses. The scale uses a star system evaluating selection of study groups, comparability of groups, and ascertainment of exposure or outcome, providing a structured, user‑friendly assessment.

Abstract

Nonrandomised studies, including case-control and cohort studies, can be challenging to implement and conduct. Assessment of the quality of such studies is essential for a proper understanding of nonrandomised studies. The Newcastle-Ottawa Scale (NOS) is an ongoing collaboration between the Universities of Newcastle, Australia and Ottawa, Canada. It was developed to assess the quality of nonrandomised studies with its design, content and ease of use directed to the task of incorporating the quality assessments in the interpretation of meta-analytic results. A 'star system' has been developed in which a study is judged on three broad perspectives: the selection of the study groups; the comparability of the groups; and the ascertainment of either the exposure or outcome of interest for case-control or cohort studies respectively. The goal of this project is to develop an instrument providing an easy and convenient tool for quality assessment of nonrandomised studies to be used in a systematic review.