Cited by 527Meta-analysis and systematic reviewsStatistical Methods in Clinical TrialsReliability and Agreement in Measurement

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Observer bias in randomized clinical trials with measurement scale outcomes: a systematic review of trials with both blinded and nonblinded assessors

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Hróbjartsson, Asbjørn, Thomsen, Ann Sofia Skou, Emanuelsson, Frida, Tendal, Britta, Hilden, Jørgen, Boutron, Isabelle, Ravaud, Philippe, Brorson, Stig·2013·Canadian Medical Association Journal

DOI 10.1503/cmaj.120744PMC PMC3589328

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Abstract

BACKGROUND: Clinical trials are commonly done without blinded outcome assessors despite the risk of bias. We wanted to evaluate the effect of nonblinded outcome assessment on estimated effects in randomized clinical trials with outcomes that involved subjective measurement scales. METHODS: We conducted a systematic review of randomized clinical trials with both blinded and nonblinded assessment of the same measurement scale outcome. We searched PubMed, EMBASE, PsycINFO, CINAHL, Cochrane Central Register of Controlled Trials, HighWire Press and Google Scholar for relevant studies. Two investigators agreed on the inclusion of trials and the outcome scale. For each trial, we calculated the difference in effect size (i.e., standardized mean difference between nonblinded and blinded assessments). A difference in effect size of less than 0 suggested that nonblinded assessors generated more optimistic estimates of effect. We pooled the differences in effect size using inverse variance random-effects meta-analysis and used metaregression to identify potential reasons for variation. RESULTS: We included 24 trials in our review. The main meta-analysis included 16 trials (involving 2854 patients) with subjective outcomes. The estimated treatment effect was more beneficial when based on nonblinded assessors (pooled difference in effect size -0.23 [95% confidence interval (CI) -0.40 to -0.06]). In relative terms, nonblinded assessors exaggerated the pooled effect size by 68% (95% CI 14% to 230%). Heterogeneity was moderate (I(2) = 46%, p = 0.02) and unexplained by metaregression. INTERPRETATION: We provide empirical evidence for observer bias in randomized clinical trials with subjective measurement scale outcomes. A failure to blind assessors of outcomes in such trials results in a high risk of substantial bias.

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Additional file 4 of The difference between shorter- versus longer-term psychotherapy for adult mental health disorders: a systematic review with meta-analysis
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Additional file 6 of Placebo response and effect in randomized clinical trials: meta-research with focus on contextual effects
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Additional file 8 of Trial-level characteristics associate with treatment effect estimates: a systematic review of meta-epidemiological studies
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Additional file 8 of Placebo response and effect in randomized clinical trials: meta-research with focus on contextual effects
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Additional file 1 of The difference between shorter- versus longer-term psychotherapy for adult mental health disorders: a systematic review with meta-analysis
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Additional file 13 of The difference between shorter- versus longer-term psychotherapy for adult mental health disorders: a systematic review with meta-analysis
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Additional file 3 of Design, delivery, and determinants of uptake: findings from a food hygiene behavior change intervention in rural Bangladesh
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Additional file 10 of Trial-level characteristics associate with treatment effect estimates: a systematic review of meta-epidemiological studies
Wang, H., Song, J., Lin, Y., Dai, W., Gao, Y., Qin, L., Chen, Y., Tam, W., Wu, I. X., & Chung, V. C. (2022) · Figshare · doi:10.6084/m9.figshare.20076593
Additional file 6 of Trial-level characteristics associate with treatment effect estimates: a systematic review of meta-epidemiological studies
Wang, H., Song, J., Lin, Y., Dai, W., Gao, Y., Qin, L., Chen, Y., Tam, W., Wu, I. X., & Chung, V. C. (2022) · Figshare · doi:10.6084/m9.figshare.20076617
Additional file 6 of The difference between shorter- versus longer-term psychotherapy for adult mental health disorders: a systematic review with meta-analysis
Juul, S., Jakobsen, J. C., Jørgensen, C. K., Poulsen, S., Sørensen, P., & Simonsen, S. (2023) · Figshare · doi:10.6084/m9.figshare.23536185
Additional file 6 of Self-determination theory interventions versus usual care in people with diabetes: a systematic review with meta-analysis and trial sequential analysis
Mathiesen, A. S., Zoffmann, V., Lindschou, J., Jakobsen, J. C., Gluud, C., Due‐Christensen, M., Rasmussen, B., Marqvorsen, E. H. S., Lund-Jacobsen, T., Skytte, T. B., et al. (2023) · Figshare · doi:10.6084/m9.figshare.24098245
Additional file 5 of Design, delivery, and determinants of uptake: findings from a food hygiene behavior change intervention in rural Bangladesh
Sobhan, S., Müller‐Hauser, A. A., Huda, T. M. N., Waid, J. L., Gautam, O. P., Gon, G., Wendt, A. S., & Gabrysch, S. (2022) · Figshare · doi:10.6084/m9.figshare.19711132
Additional file 4 of Blinding of study statisticians in clinical trials: a qualitative study in UK clinical trials units
Iflaifel, M., Partlett, C., Bell, J., Cook, A., Gamble, C. L., Julious, S., Juszczak, E., Linsell, L., Montgomery, A., & Sprange, K. (2022) · Figshare · doi:10.6084/m9.figshare.20168895
Additional file 12 of The difference between shorter- versus longer-term psychotherapy for adult mental health disorders: a systematic review with meta-analysis
Juul, S., Jakobsen, J. C., Jørgensen, C. K., Poulsen, S., Sørensen, P., & Simonsen, S. (2023) · Figshare · doi:10.6084/m9.figshare.23536203
Additional file 10 of The difference between shorter- versus longer-term psychotherapy for adult mental health disorders: a systematic review with meta-analysis
Juul, S., Jakobsen, J. C., Jørgensen, C. K., Poulsen, S., Sørensen, P., & Simonsen, S. (2023) · Figshare · doi:10.6084/m9.figshare.23536197
Additional file 5 of Trial-level characteristics associate with treatment effect estimates: a systematic review of meta-epidemiological studies
Wang, H., Song, J., Lin, Y., Dai, W., Gao, Y., Qin, L., Chen, Y., Tam, W., Wu, I. X., & Chung, V. C. (2022) · Figshare · doi:10.6084/m9.figshare.20076614
Additional file 1 of Internet psychotherapeutic interventions for anxiety disorders – a critical evaluation
Bandelow, B., & Wedekind, D. (2022) · Figshare · doi:10.6084/m9.figshare.20193921
Additional file 19 of The difference between shorter- versus longer-term psychotherapy for adult mental health disorders: a systematic review with meta-analysis
Juul, S., Jakobsen, J. C., Jørgensen, C. K., Poulsen, S., Sørensen, P., & Simonsen, S. (2023) · Figshare · doi:10.6084/m9.figshare.23536224
Additional file 4 of Self-determination theory interventions versus usual care in people with diabetes: a systematic review with meta-analysis and trial sequential analysis
Mathiesen, A. S., Zoffmann, V., Lindschou, J., Jakobsen, J. C., Gluud, C., Due‐Christensen, M., Rasmussen, B., Marqvorsen, E. H. S., Lund-Jacobsen, T., Skytte, T. B., et al. (2023) · Figshare · doi:10.6084/m9.figshare.24098239
Additional file 4 of Placebo response and effect in randomized clinical trials: meta-research with focus on contextual effects
Hafliðadóttir, S. H., Juhl, C. B., Nielsen, S. M., Henriksen, M., Harris, I. A., Bliddal, H., & Christensen, R. (2021) · Figshare · doi:10.6084/m9.figshare.15058023
Additional file 2 of Design, delivery, and determinants of uptake: findings from a food hygiene behavior change intervention in rural Bangladesh
Sobhan, S., Müller‐Hauser, A. A., Huda, T. M. N., Waid, J. L., Gautam, O. P., Gon, G., Wendt, A. S., & Gabrysch, S. (2022) · Figshare · doi:10.6084/m9.figshare.19711123
Additional file 15 of The difference between shorter- versus longer-term psychotherapy for adult mental health disorders: a systematic review with meta-analysis
Juul, S., Jakobsen, J. C., Jørgensen, C. K., Poulsen, S., Sørensen, P., & Simonsen, S. (2023) · Figshare · doi:10.6084/m9.figshare.23536212
Additional file 3 of Self-determination theory interventions versus usual care in people with diabetes: a systematic review with meta-analysis and trial sequential analysis
Mathiesen, A. S., Zoffmann, V., Lindschou, J., Jakobsen, J. C., Gluud, C., Due‐Christensen, M., Rasmussen, B., Marqvorsen, E. H. S., Lund-Jacobsen, T., Skytte, T. B., et al. (2023) · Figshare · doi:10.6084/m9.figshare.24098236
Additional file 7 of Trial-level characteristics associate with treatment effect estimates: a systematic review of meta-epidemiological studies
Wang, H., Song, J., Lin, Y., Dai, W., Gao, Y., Qin, L., Chen, Y., Tam, W., Wu, I. X., & Chung, V. C. (2022) · Figshare · doi:10.6084/m9.figshare.20076620
Additional file 9 of The difference between shorter- versus longer-term psychotherapy for adult mental health disorders: a systematic review with meta-analysis
Juul, S., Jakobsen, J. C., Jørgensen, C. K., Poulsen, S., Sørensen, P., & Simonsen, S. (2023) · Figshare · doi:10.6084/m9.figshare.23536194
Additional file 3 of Trial-level characteristics associate with treatment effect estimates: a systematic review of meta-epidemiological studies
Wang, H., Song, J., Lin, Y., Dai, W., Gao, Y., Qin, L., Chen, Y., Tam, W., Wu, I. X., & Chung, V. C. (2022) · Figshare · doi:10.6084/m9.figshare.20076608
Additional file 2 of Placebo response and effect in randomized clinical trials: meta-research with focus on contextual effects
Hafliðadóttir, S. H., Juhl, C. B., Nielsen, S. M., Henriksen, M., Harris, I. A., Bliddal, H., & Christensen, R. (2021) · Figshare · doi:10.6084/m9.figshare.15058017
Additional file 3 of Placebo response and effect in randomized clinical trials: meta-research with focus on contextual effects
Hafliðadóttir, S. H., Juhl, C. B., Nielsen, S. M., Henriksen, M., Harris, I. A., Bliddal, H., & Christensen, R. (2021) · Figshare · doi:10.6084/m9.figshare.15058020
Additional file 5 of Placebo response and effect in randomized clinical trials: meta-research with focus on contextual effects
Hafliðadóttir, S. H., Juhl, C. B., Nielsen, S. M., Henriksen, M., Harris, I. A., Bliddal, H., & Christensen, R. (2021) · Figshare · doi:10.6084/m9.figshare.15058026
Additional file 7 of Placebo response and effect in randomized clinical trials: meta-research with focus on contextual effects
Hafliðadóttir, S. H., Juhl, C. B., Nielsen, S. M., Henriksen, M., Harris, I. A., Bliddal, H., & Christensen, R. (2021) · Figshare · doi:10.6084/m9.figshare.15058032

Authors: Hróbjartsson, A., Thomsen, A. S. S., Emanuelsson, F., Tendal, B., Hilden, J., Boutron, I., Ravaud, P., & Brorson, S.
Affiliations: University of Copenhagen (DK)
ORCID: Hróbjartsson, Asbjørn
Thomsen, Ann Sofia Skou
Emanuelsson, Frida
Tendal, Britta
Hilden, Jørgen
Boutron, Isabelle
Ravaud, Philippe
Brorson, Stig
Venue: Canadian Medical Association Journal
Publisher: CMA Impact Inc.
Published: 2013-01-28
Volume: 185
Issue: 4
Pages: E201-E211
ISSN: 0820-3946 (ISSN-L)
1488-2329
DOI: 10.1503/cmaj.120744
PMC: PMC3589328
OpenAlex: W2006175454
Cited by: 527
References: 52
Citations by year: 2026: 30 · 2025: 26 · 2024: 23 · 2023: 54 · 2022: 46 · 2021: 43 · 2020: 35 · 2019: 45 · 2018: 51 · 2017: 31 · 2016: 54 · 2015: 37 · 2014: 29 · 2013: 21
FWCI: 9.63
Type: journal article
Language: en
Open access: gold
doi.org
Locations: Canadian Medical Association Journal (publishedVersion)
Europe PMC (PubMed Central) (publishedVersion)
PubMed Central (publishedVersion)
PubMed (publishedVersion)
Research at the University of Copenhagen (University of Copenhagen) (submittedVersion)
Funders: U.S. Department of Veterans Affairs
Topics: Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Meta-analysis and systematic reviews
Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Clinical Trials
Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Reliability and Agreement in Measurement
Keywords: observer bias, subjective outcomes, risk of bias, effect size estimation, bias in clinical trials
MeSH terms: Double-Blind Method, Observer Variation, Randomized Controlled Trials as Topic, Outcome Assessment, Health Care

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Observer bias in randomized clinical trials with measurement scale outcomes: a systematic review of trials with both blinded and nonblinded assessors

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