Original ArticleSelf-reported information on the diagnosis of colorectal cancer was reliable but not necessarily valid
Introduction
In the United States of America, Europe, and most of the industrialized world, colorectal cancer is the third most common cancer and the second most common cause of cancer deaths [1], [2], [3]. Risk increases progressively with age, and the incidence of colorectal cancer is expected to increase as worldwide trends in population aging continue [1].
The process of diagnosis for colorectal cancer is often characterized by multiple symptoms and a number of diagnostic tests. Symptoms may range from the acute, such as rectal bleeding, to more general, constitutional complaints, such as lethargy and loss of appetite. Symptoms may not be apparent until late in the disease course, and as a result, colorectal cancer is often diagnosed at an advanced stage [4]. Patients sometimes undergo a number of tests before a conclusive diagnosis is made.
Self-report is a common method of obtaining data pertaining to symptoms and diagnostic tests for epidemiologic studies, primarily because it is easy to implement and is inexpensive [5], [6], [7], [8]. However, self-reported data may be limited by a number of factors, such as recall error, biases such as social desirability and acquiesce, and by poorly constructed measures [7], [9], [10], [11].
There is a scarcity of data on the reliability of self-reported colorectal cancer symptoms. Malats et al. [12] compared hospital records with interview data to assess agreement on the initial symptom experienced by patients with cancer of the digestive tract (just over half had colorectal cancer). They found that the concordance between hospital records and interview data was 61% for type of first symptom, with only 46% agreement for the date of first symptom (within 30 days).
A number of studies have assessed the validity of self-reported testing for colorectal cancer [5], [13], [14], [15], [16]. However, these studies focused on colorectal cancer screening in the general population. There are no published data on the validity of self-reported diagnostic testing among colorectal cancer patients. Most studies of the validity of self-reported screening tests found at least moderate agreement between self-report and other, more objective data [13], [14], [15], [16]. Colonoscopy and sigmoidoscopy were more accurately recalled than fecal occult blood testing; recall was generally better for more invasive tests [5], [14]. A common finding was that participants tended to report having had screening tests more recently than had been the case.
We examined the test–retest reliability and the validity of patient self-report on key elements of the process of diagnosis of colorectal cancer.
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Sample
One hundred and eighty-one adults were randomly selected from participants in a population-based, longitudinal study of the diagnosis of colorectal cancer and the quality of life following diagnosis. All had been diagnosed with a first, primary diagnosis of colorectal cancer between January 1, 2003 and December 31, 2004, were aged between 20 and 80 years, and had been recruited through the Queensland Cancer Registry. During a telephone interview, these 181 potential participants were asked
Results
The mean and median time between Interview 1 and Interview 2 was 34 days (range = 27–44 days). The sociodemographic and disease-related characteristics of the study participants are presented in Table 2.
Discussion
To our knowledge, this is the first study to assess the test–retest reliability and validity of self-reported cancer diagnostic tests. Such information is important because self-report will continue to be widely used in cancer epidemiology studies. Our findings suggest that the accuracy of self-reported diagnostic information is variable, depending on the type of information being elicited. Overall, we found the test–retest reliability to be moderate to high, and the validity moderate to poor.
Acknowledgments
The authors wish to acknowledge the general practitioners who kindly completed the questionnaires for this study. This project was funded by The Cancer Council Queensland.
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