Saturday, July 19, 2008

Neoplasms: 12

This is the twelfth blog in a series of blogs on neoplasia.

In the past few blogs, I've been trying to explain the disconnect between cancer survival data and cancer death rate data. The cancer survival data seems to indicate that we're making enormous improvements in cancer treatment. The cancer death rate indicates that Americans are dying from cancer at about the same rate as they had been a half-century ago.

Several days ago, I listed over a dozen biases in cancer survival data that contribute to an overly optimistic sense of medical progress.

In this and the next few blogs, I thought I'd review some of these biases. The purpose of this exercise is to explain that the interpretation of survival data is enormously complex and that survival data is probably not the best way to gauge progress in the field of cancer research.

Today, let's look at Medical Record and Re-abstraction Biases.

Trialists draw information related to the diagnosis, treatment, and outcome of patients by reviewing medical records. The quality of medical research often depends on the quality of medical records. When medical records are incomplete, incorrect, illegible, or otherwise uninterpretable, the results for an otherwise well-planned clinical trial can be disastrous.

Cause of death data comes from death certificates RfreaR. Death certificate data have many deficiencies [1,2]. The most common error occurs when a mode of death is listed as the cause of death. For example, cardiac arrest is not a cause of death, though it appears as the cause of death on many death certificates. There is not much value in a death certificate for a man who died with end-stage cancer when the listed cause of death is "cardia arrest." An international survey has shown very little consistency in the way that death data are collected [3]. Death certificates are completed without the benefit of an autopsy. At best, death certificates express a clinician's reasonable judgement at the time of a patient's death.

What do researchers do when they find that their medical records are inadequate. Often, they resort to re-abstraction, a time-consuming, expensive and occasionally futile undertaking. Re-abstraction often involves revisiting charts, visiting outpatient clinics and the private offices of medical doctors, re-interviewing patients and families, and a host of extraordinary efforts aimed at restoring credibility to clinical trial data. If a subset of patients has better maintained records than another subset, a bias can be introduced to the trial.

1. [Ashworth TG: Inadequacy of death certification: proposal for change. J Clin Pathol 44:265, 1991. Comment. A British perspective on the importance of the death certificate.]

2. [Kircher T, Anderson RE: Cause of death: proper completion of the death certificate. JAMA 258:349-352, 1987. Comment. Though every physician is expected to complete death certificates, surprisingly few physicians understand how to do the job. As a consequence, death certificates are notoriously inadequate records of the cause of death. The authors explain the differences between the underlying and immediate causes of death, between the mechanism and manner of death. They also describe how to complete the medical certification section of the death certificate.]

3. [Walter SD, Birnie SE: Mapping mortality and morbidity patterns: an international comparison. Intl J Epidemiology 20:678-689, 1991. Comment. This survey of 49 national and international health atlases has shown that there is virtually no consistency in the way that death data are presented.]

-Copyright (C) 2008 Jules J. Berman

key words: cancer, tumor, tumour, carcinogen, neoplasia, neoplastic development, classification, biomedical informatics, tumor development, precancer, benign tumor, ontology, classification, developmental lineage classification and taxonomy of neoplasms

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