assessing quality of individual studies

Assessing the Quality of Individual Studies

Prepared for:

The Agency for Healthcare Research and Quality (AHRQ)

Training Modules for Systematic Reviews Methods Guide

www.ahrq.gov

Systematic Review Process Overview

To describe the concept of quality assessment

To identify reasons for quality assessment

To list the steps in quality assessment

To describe and report the methods for quality assessment

Learning Objectives

Definition of quality:“[T]he extent to which all aspects of a study’s design and conduct

can be shown to protect against systematic bias, nonsystematic bias, and inferential error.” (Lohr & Carey, 1999)

Considered to be synonymous with internal validity

Relevant for individual studies

Distinct from assessment of risk of bias for a body of evidence

What Is Quality Assessment?

Lohr KN, Cary TS. Jt Comm J Qual Improv 1999;25:470-9.

Systematic Errors: Include selection bias and confounding, in which values tend to be

inaccurate in a particular direction

Nonsystematic Errors:Are attributable to chance

Inferential Errors:Result from problems in data analysis and interpretation, such as

choice of the wrong statistical measure or wrongly rejecting the null hypothesis

What Are the Components of Quality Assessment?

Lohr KN, Cary TS. Jt Comm J Qual Improv 1999;25:470-9.

Consider the Contribution of an Individual Study to the Body of Evidence

Quality (systematic error and inferential error, type of study)

Size of study (nonsystematic or random error)

Direction and magnitude of results

Relevance of results to key questions

Risk of Bias

Precision

Directness

Consistency

Applicability

Owens DK, et al. In: Methods guide for comparative effectiveness reviews. Available at: http://effectivehealthcare.ahrq.gov/ehc/products/60/318/2009_0805_grading.pdf.

Direct vs. indirect comparisons, health outcomes vs. surrogate outcomes

Quality assessment is required for:Interpreting results

Grading the strength of the body of evidence

Quality assessment may also be used for:Selecting studies for the review (based on a priori assessment of

evidence gaps)

Selecting studies for qualitative synthesis

Selecting studies for quantitative synthesis

Interpreting heterogeneous findings

Reasons for Quality Assessment

1. Classify the study design

2. Apply predefined criteria for quality assessment of each outcome based on:Study design — sources of bias may vary by design

Study conduct — poor study conduct and discrepancy between design and conduct may increase risk of bias

Reporting — quality assessment may be influenced by adequacy of reporting when information on study design and conduct are missing

What Are the Steps in Quality Assessmentof Each Individual Study (I)?

Helfand M, Balshem H. In: Helfand M, Balshem H. In: Methods guide for comparative effectiveness reviews. Available at: http://www.effectivehealthcare.ahrq.gov/ehc/products/60/294/2009_0805_principles1.pdf.

.

3. Arrive at a summary judgment of the study’s quality to rate studies good, fair, or poorRequires resolution of conflicts when two reviewers

independently evaluate quality

What Are the Steps in Quality Assessment of Each Individual Study (II)?


Did the study have more than one group or arm? If so, was a control group present?

Did investigators have control over allocation and timing of the intervention?

Did investigators randomly allocate subjects to interventions?

Did investigators concurrently measure intervention and exposure status for intervention and comparison groups?

Did investigators concurrently measure outcomes for intervention and comparison groups?

Questions To ConsiderWhen Classifying Study Design

Select a tool that is based on coverage of important criteria

Based on the topic, select and apply one of several available tools that consider and explain how to evaluate:Similarity of groups at baseline in terms of baseline characteristics

and prognostic factors

Validity of primary outcomes

Blinded measurement of outcomes

Apply Predefined Criteria for All Study Types (I)

Helfand M, Balshem H. In: Methods guide for comparative effectiveness reviews. Available at: http://www.effectivehealthcare.ahrq.gov/ehc/products/60/294/2009_0805_principles1.pdf.

Apply one of several available tools that considerIntention-to-treat analysis

Differential loss to followup between the compared groups or overall high loss to followup

Conflict of interest

Apply Predefined Criteria for All Study Types (II)

Methods used for randomization

Allocation concealment

Blinding of subjects and providers

Additional Criteria for Trials


Sample size, width of confidence intervals, or power

Methods for selecting participantsInception cohort, methods to adjust for or avoid selection bias

Methods for measuring exposure variables

Additional Criteria for Observational Studies (I)


Methods for dealing with any design-specific issues such as recall bias and interviewer bias

Analytical methods to control confoundingMatching, stratification, multivariate analysis, or other statistical

adjustment

Additional Criteria for Observational Studies (II)


After assessment of individual criteria, assign ratings of “good,” “fair,” or “poor” (attributes described in later slides)

Assess quality for each outcome of interest

Base ratings on the evaluation of likely effect of design or execution flaws on internal validity, rather than a nominal failure to meet every quality criterion

Adjudicate differences between raters in a transparent manner when two raters independently assess overall quality

Arrive at a Comprehensive Judgment of Quality


Design and conduct of study address risk of bias

Appropriate measurement of outcomes

Appropriate statistical and analytical methods

Low drop-out rates

Adequate reporting of statistical and analytical methods, drop-out rates and reasons, and outcomes (no reporting errors)

Attributes of Good-Quality Studies


Do not meet all the criteria required for a rating of good quality

No flaw is likely to cause major bias

Missing information often drives rating

Attributes of Fair-Quality Studies


Significant biasesInappropriate design, conduct, analysis, or reporting

Large amounts of missing information

Discrepancies in reporting

Attributes of Poor-Quality Studies


Poor-quality studies may be excluded or included

Base decisions on gaps in current evidence and availability of good-quality or fair-quality studies

Justify selective inclusion of poor-quality studies for subgroups or subquestions

Treatment of Poor-Quality Studies in the Review

Accompany overall quality rating for individual studies with a statement of:Flaws in the design or execution of a study

The potential consequences of that flaw

Report the criteria and the process used to arrive at a quality rating

Reporting Quality Ratings

Quality assessment:Is synonymous with internal validity

Refers to individual studies

Contributes to, but is separate from, the evaluation of the risk of systematic bias for the body of evidence

Key Messages (I):Definition of Quality Assessment

Results of quality assessment are used in multiple steps in the systematic review process, from final inclusion of studies to interpretation of evidence

Steps in quality assessmentStudy design classification

Assessment of individual quality criteria

Summary judgment of the study quality

Key Messages (II): Rationale of and Steps in Quality Assessment

Transparency of processFull reporting of all elements of quality for each individual study

Explicit description (and examples) of how each criterion was operationalized

Clear reporting of how team members scored quality

Description of how conflicts between raters were resolved

Transparency of judgmentExplanation of final rating

Key Messages (III): Reporting

Deeks JJ, Dinnes J, D’Amico R, et al, for the International Stroke Trial Collaborative Group and the European Carotid Surgery Trial Collaborative Group. Evaluating non-randomised intervention studies. Health Technol Assess 2003;7(27):iii-x,1-173.

Hartling L, Bond K, Harvey K, et al. Developing and testing a tool for the classification of study designs in systematic reviews of interventions and exposures. (Prepared by the University of Alberta Evidence-based Practice Center under contract no. 290-02-0023.) In press.

Helfand M, Balshem H. Principles in developing and applying guidance. In: Methods guide for comparative effectiveness reviews. Rockville, MD: Agency for Healthcare Research and Quality, Posted August 2009. Available at: http://www.effectivehealthcare.ahrq. gov/ehc/products/ 60/294/2009_0805_principles1.pdf.

References (I)

Lohr KN, Carey TS. Assessing “best evidence”: issues in grading the quality of studies for systematic reviews. Jt Comm J Qual Improv 1999;25:470-9.

Owens DK, Lohr KN, Atkins D, et al. Grading the strength of a body of evidence when comparing medical interventions. In: Methods guide for comparative effectiveness reviews. Rockville, MD: Agency for Healthcare Research and Quality, Posted July 2009. Available at: http://effectivehealthcare.ahrq.gov/ehc/products/60/318/2009_0805_grading.pdf.

Sanderson S, Tatt ID, Higgins JP. Tools for assessing quality and susceptibility to bias in observational studies in epidemiology: a systematic review and annotated bibliography. Int J Epidemiol 2007;36:666-76.

References (II)

West S, King V, Carey TS, et al. Systems to Rate the Strength of Scientific Evidence, Evidence Report/Technology Assessment No. 47 (Prepared by the Research Triangle Institute–University of North Carolina Evidence-based Practice Center under Contract No. 290-97-0011. Rockville, MD: Agency for Healthcare Research and Quality, March 2002. AHRQ Publication No. 02-E015. Available at: http://www.ahrq.gov/clinic/epcsums/strengthsum.pdf.

Whiting P, Rutjes AWS, Dinnes J, et al. Development and validation of methods for assessing the quality of diagnostic accuracy studies. Health Technol Assess 2004;8(25):iii, 1-234.

References (III)

This presentation was prepared by Meera Viswanathan, Ph.D., a member of the Research Triangle Institute–University of North Carolina Evidence-based Practice Center.

The presentation is based on an update of chapter 6 in version 1.0 of the Methods Guide for Comparative Effectiveness Reviews (update available at: http://www.effectivehealthcare. ahrq.gov/ehc/products/60/294/2009_0805_principles1.pdf).

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assessing quality of individual studies

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