---

name: risk-of-bias description: Use when assessing risk of bias or study quality. Covers RoB 2 for RCTs, Newcastle-Ottawa Scale for cohorts, ROBINS-I for non-randomized interventions, and QUADAS-2 for diagnostic studies. Invoke for quality assessment.

Risk of Bias Assessment Skill

This skill guides risk of bias and study quality assessment for systematic reviews.

When to Use

Invoke this skill when the user:

• Asks to assess risk of bias
• Needs quality assessment of studies
• Mentions RoB 2, NOS, ROBINS-I, or QUADAS-2
• Wants to evaluate study quality
• Needs a risk of bias table or plot

Tool Selection

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RoB 2 (Cochrane Risk of Bias 2)

For randomized controlled trials.

Domains

Judgments

• Low risk: No concerns in this domain
• Some concerns: Some concern but not definitely high risk
• High risk: Definitely high risk in this domain

Overall Judgment

CopyIf ALL domains are "Low risk" → Overall: Low risk
If ANY domain is "High risk" → Overall: High risk
Otherwise → Overall: Some concerns

R Code for Visualization

Copylibrary(robvis)

# Prepare data
rob_data <- data.frame(
  Study = c("Smith 2020", "Jones 2021", "Brown 2022"),
  D1 = c("Low", "Some concerns", "Low"),
  D2 = c("Low", "Low", "High"),
  D3 = c("Low", "Low", "Low"),
  D4 = c("Some concerns", "Low", "Low"),
  D5 = c("Low", "Low", "Low"),
  Overall = c("Some concerns", "Some concerns", "High")
)

# Traffic light plot
png("rob_traffic_light.png", width=1000, height=600, res=150)
rob_traffic_light(rob_data, tool = "ROB2")
dev.off()

# Summary plot
png("rob_summary.png", width=800, height=400, res=150)
rob_summary(rob_data, tool = "ROB2")
dev.off()

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Newcastle-Ottawa Scale (NOS)

For observational studies (cohort and case-control).

Cohort Studies (max 9 stars)

Selection (max 4 stars)

Comparability (max 2 stars)

Outcome (max 3 stars)

Quality Categories

Copy7-9 stars: High quality
4-6 stars: Moderate quality
0-3 stars: Low quality

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ROBINS-I

For non-randomized studies of interventions.

Domains

Judgments

• Low risk: Comparable to well-performed RCT
• Moderate risk: Sound for non-randomized study
• Serious risk: Important problems
• Critical risk: Study too problematic to provide evidence
• No information: Insufficient information

Overall Judgment

CopyIf ALL domains are "Low" → Overall: Low risk
If highest is "Moderate" → Overall: Moderate risk
If ANY domain is "Serious" → Overall: Serious risk
If ANY domain is "Critical" → Overall: Critical risk

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QUADAS-2

For diagnostic accuracy studies.

Domains

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Output Format

Risk of Bias Table

Copyrisk_of_bias:
  - study_id: "Smith2023"
    tool: "RoB2"
    domains:
      D1_randomization: "Low"
      D2_deviations: "Some concerns"
      D3_missing_data: "Low"
      D4_measurement: "Low"
      D5_reporting: "Low"
    overall: "Some concerns"
    support: "Blinding of outcome assessors unclear"

Summary Reporting

Copy## Risk of Bias Assessment

We used the Cochrane RoB 2 tool for randomized trials.

**Summary:**
- Low risk: 5 studies (45%)
- Some concerns: 4 studies (36%)
- High risk: 2 studies (18%)

**Key concerns:**
- Outcome assessment blinding unclear in 4 studies
- Per-protocol analysis without addressing deviations in 2 studies

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Best Practices

1. Two reviewers: Independent assessment
2. Pilot testing: Calibrate on 2-3 studies
3. Support quotes: Document rationale with paper quotes
4. Domain-level: Report each domain, not just overall
5. Sensitivity analysis: Exclude high risk studies

Integration with Meta-Analysis

Copy# Subgroup by risk of bias
forest(ma, subgroup = rob_overall,
       subgroup.levels = c("Low", "Some concerns", "High"))

# Sensitivity: low risk only
ma_low <- update(ma, subset = rob_overall == "Low")
summary(ma_low)