This article covers how to complete a Risk of Bias assessment using the Newcastle-Ottawa Scale (NOS). Rayyan offers NOS in two versions: one for cohort studies and one for case-control studies. Both use the same three-domain star system. They differ in the items asked under Selection and in the third domain, which is Outcome for cohort studies and Exposure for case-control studies. For an overview of all available tools and how to add articles, see How to Assess Risk of Bias in Rayyan.
Select NOS for your article
- In the Risk of bias tab, open the dropdown in the Tool column for the article.
- Hover over NOS and choose Cohort or Case-control, depending on the study's design.
- Click Start assessment or double-click the article to open it. The article's full text opens with the assessment panel alongside it.
The panel shows NOS (cohort) or NOS (case-control) as the risk of bias tool, with a progress bar that tracks how many of the three domains you have completed. Each domain shows how many of its items you have answered and, once you start, its star score. Click Guide at any time for guidance on the scale.
How scoring works
NOS awards stars across three domains, up to a total of 9 ★. Domain and total scores update automatically as you answer each item, and recalculate if you change an answer. Every item also has an optional Comments field for your reasoning.
| Domain | Cohort studies | Case-control studies | Maximum stars |
|---|---|---|---|
| Domain 1 | Selection | Selection | 4 ★ |
| Domain 2 | Comparability | Comparability | 2 ★ |
| Domain 3 | Outcome | Exposure | 3 ★ |
Rayyan sets the overall risk level from the total score. The thresholds are the same for both versions:
| Total score | Overall risk |
|---|---|
| 7 to 9 ★ | Low risk |
| 4 to 6 ★ | Moderate risk |
| 0 to 3 ★ | High risk |
Cohort studies
Domain 1: Selection (max 4 ★)
Answer all four items. Each item awards up to 1 star based on the answer you select.
| Item and answer | Stars |
|---|---|
| S1. Representativeness of the exposed cohort | |
| Truly representative of the average exposed in the community | 1 ★ |
| Somewhat representative of the average exposed in the community | 1 ★ |
| Selected group of users (e.g. nurses, volunteers) | 0 ★ |
| No description of the derivation of the cohort | 0 ★ |
| S2. Selection of the non-exposed cohort | |
| Drawn from the same community as the exposed cohort | 1 ★ |
| Drawn from a different source | 0 ★ |
| No description of the derivation of the non-exposed cohort | 0 ★ |
| S3. Ascertainment of exposure | |
| Secure record (e.g. surgical records) | 1 ★ |
| Structured interview | 1 ★ |
| Written self-report | 0 ★ |
| No description | 0 ★ |
| S4. Demonstration that outcome of interest was not present at start of study | |
| Yes | 1 ★ |
| No | 0 ★ |
Domain 2: Comparability (max 2 ★)
A single multi-select item. Select both options to award 2 stars.
| Item and answer | Stars |
|---|---|
| C1. Comparability of cohorts on the basis of the design or analysis (select one or both) | |
| Study controls for the most important factor | 1 ★ |
| Study controls for any additional factor (awarded in addition to the above) | +1 ★ |
Domain 3: Outcome (max 3 ★)
Answer all three items. Each item awards up to 1 star based on the answer you select.
| Item and answer | Stars |
|---|---|
| O1. Assessment of outcome | |
| Independent blind assessment | 1 ★ |
| Record linkage | 1 ★ |
| Self-report | 0 ★ |
| No description | 0 ★ |
| O2. Was follow-up long enough for outcomes to occur? | |
| Yes | 1 ★ |
| No | 0 ★ |
| O3. Adequacy of follow-up of cohorts | |
| Complete follow-up, all subjects accounted for | 1 ★ |
| Subjects lost to follow-up unlikely to introduce bias (small number lost, or description provided) | 1 ★ |
| Follow-up rate below adequate threshold and no description of those lost | 0 ★ |
| No statement | 0 ★ |
Case-control studies
Domain 1: Selection (max 4 ★)
Answer all four items. Each item awards up to 1 star based on the answer you select.
| Item and answer | Stars |
|---|---|
| S1. Is the case definition adequate? | |
| Yes, with independent validation | 1 ★ |
| Yes, e.g. record linkage or based on self-reports | 0 ★ |
| No description | 0 ★ |
| S2. Representativeness of the cases | |
| Consecutive or obviously representative series of cases | 1 ★ |
| Potential for selection biases or not stated | 0 ★ |
| S3. Selection of controls | |
| Community controls | 1 ★ |
| Hospital controls | 0 ★ |
| No description | 0 ★ |
| S4. Definition of controls | |
| No history of disease (endpoint) | 1 ★ |
| No description of source | 0 ★ |
Domain 2: Comparability (max 2 ★)
A single multi-select item. Select both options to award 2 stars.
| Item and answer | Stars |
|---|---|
| C1. Comparability of cases and controls on the basis of the design or analysis (select one or both) | |
| Study controls for the most important factor | 1 ★ |
| Study controls for any additional factor (awarded in addition to the above) | +1 ★ |
Domain 3: Exposure (max 3 ★)
Answer all three items. Each item awards up to 1 star based on the answer you select.
| Item and answer | Stars |
|---|---|
| E1. Ascertainment of exposure | |
| Secure record (e.g. surgical records) | 1 ★ |
| Structured interview where blind to case/control status | 1 ★ |
| Interview not blinded to case/control status | 0 ★ |
| Written self-report or medical record only | 0 ★ |
| No description | 0 ★ |
| E2. Same method of ascertainment for cases and controls | |
| Yes | 1 ★ |
| No | 0 ★ |
| E3. Non-response rate | |
| Same rate for both groups | 1 ★ |
| Non-respondents described | 0 ★ |
| Rate different and no designation | 0 ★ |
Review the overall risk and complete the assessment
When all three domains are complete, the panel shows the Overall risk assessment (Low risk, Moderate risk, or High risk) next to the total score, for example 7/9 ★. The same result appears in the Overall risk column of the assessment table.
At the same point, an optional overall note field appears. It is a single note for the whole assessment, covering all three domains, so use it to record your overall interpretation of the study's quality.
- Click Save changes at any point to save your progress and come back later. The status changes to In progress after the first save.
- Mark as completed becomes available once every item in all three domains is answered. Click it to finish the assessment. The status changes to Complete.
Like RoB 2 and MMAT, the NOS form is fixed, so you cannot add, remove, or reword its items. This keeps your assessment aligned with the published scale and comparable to other reviews that use it.