Blinding in Clinical Trials and Other Studies


According to Day and Altman 2000, p.504, “human behavior is influenced by what we know or believe”. This is a factor that has a significant impact on clinical trials, as we have both patients and health care professionals involved in clinical trials and their behavior during the clinical trial is likely to be conditioned by what they know and believe. Blinding or masking is the attempt in clinical trials to nullify the impact of this bias on the results and the reliability of the clinical trial (Day & Altman, 2000).

Considerations and Practicalities

There are two elements involved in the validity of the study, the first being the internal validity of the study and the second is the external validity of the study. The internal validity involves the design and conduct of the clinical trial, whereby only the differences in the planned interventions impact on the outcomes and nothing else. The strength of the internal validity impinges on the acceptance of the findings of the study or the external validity of the clinical. Blinding is a measure used to reduce bias and strengthen the internal validity of the study (Paradis, 2008).

However, blinding at what may be considered ideal levels, wherein all participants subjects, operators and investigators are kept oblivious to the interventions and the subjects under selected interventions my not be possible in all clinical trials, and hence design of clinical trials does involve single blinding. In single blinding the subjects are kept masked from the type of intervention (Day & Altman, 2000).

In the proposed study on central venous catheters (CVCs) it is not possible to employ a double blinded study, as the different CVCs are clearly identified for patient safety and any interference in patient safety would run against the ethics of clinical research (Licciardone & Russo, 2006).

The reduction of the level of blinding brings about the need for the introduction of protocols to increase the validity of the study. The introduction of such protocols in the clinical trial on CVCs calls for the fixed time schedules in the testing of blood for infection instead on the basis clinical necessity or observation, to remove the subjective bias of the health care staff involved in the drawing of blood for the testing purpose. This would also ensure that the same number of blood samples are drawn in the case of every intervention used for the study (Licciardone & Russo, 2006).

Since there is only partial blinding at the subject end, there is the requirement of blinding the laboratory staff involved in the testing of the blood from the different interventions being compared to remove any bias on their part. This makes it necessary for a set of standard protocols to be introduced at the subject end or in the several clinics where the subjects are present and the clinical study is coordinated. This standard protocol would involve coding the blood drawn from the several subjects in such a manner as to make it impossible for the testing laboratory staff to identify the intervention used against the sample drawn, but at the same time makes it possible for the study team to collate the test results against the type of intervention employed on the subject (Licciardone & Russo, 2006).


The fixed time schedule for drawing of blood for testing along with the standard protocol to ensure anonymity of the blood samples sent for testing would reduce the impact bias due to lower level blinding in the research methodology, increasing its internal validity and through that its external validity.

Literary References

Day, S. J. & Altman, D.J. 2000, ‘Blinding in clinical trials and other studies’, BMJ, vol.321, pp.504.

Licciardone, J. C. & Russo, D. P. 2006, ‘Blinding Protocols, Treatment Credibility and Expectancy: Methodological Issues in Clinical Trials of Osteopathic Manipulative Treatment’, Journal of the American Osteopathic Association, vol.106, no.8, pp.457-463.

Paradis, C. 2008, ‘Bias in Surgical Research’, Annals of Surgery, vol.248, no.2, pp.180-188.

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