Assessment of Diagnostic Technology in Health Care Rationale, Methods, Problems, and Directions (1989) / Chapter Skim
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4. Primary Assessment of Diagnostic Tests: Barriers to Implementation
4. Primary Assessment of Diagnostic Tests: Barriers to Implementation
Pages 73-106
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From page 73... ...
We win also address briefly a number of methodological issues concerning the interpretation and reporting of Be study data. Five specific stages of a primary technology assessment win be addressed: planning and protocol development, recruitment, implementation, interpretation, aIld reporting.
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From page 74... ...
~ choosing the clinical problem to be evaluated in a diagnostic technology assessment, policy-or~ented investigators would use cr~tena such as me frequency of a condition, He cost of the technology, and the potential impact of He study result on clinical practice. Other factors that might influence the choice include the potential effect of He test on patient management and outcome and deficiencies in existing diagnostic methods (Figure 4.1)
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From page 75... ...
EXISTING DIAGNOSTIC METHODS INADEQUATE? FIGURE 4.1 Factors that influence the choice of die clinical condition to be studied.
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From page 76... ...
Patient Population The study population must be weD defined. When certain subsets of eligible patients are excluded because of other, coexisting disease, a physician may be unable to generalize the study result to me whole spectrum of patients encountered in clinical practice.
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From page 77... ...
Fineberg has proposed the foBow~ng hierarchy for the evaluation of diagnostic tests: technical capability, diagnostic accuracy, therapeutic impact, and impact on patient outcome Iceberg et al.
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From page 78... ...
The design of a technology assessment influences the feasibility of conducting each type of study. In a randomized design, each patient undergoes only one of the study tests; in a nonrandomized design, each patient would undergo all of the study tests, although randomization may be used to assign a patient to a particular sequence of tests.
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From page 79... ...
ONLY ONE CODY TEST RESULT) FIGURE 4~2 Alternative combinations of endpoint and study design.
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From page 80... ...
Consider a study designed to assess the diagnostic accuracy of barium enema (BE) in detecting colonic polyps (also see Figure 4.31.
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From page 81... ...
There would not be a protocol for subsequent patient care. A study of efficacy should assess the potential benefit of the technology when applied to a specific clinical problem in a defined population under ideal conditions.
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From page 82... ...
The "clean" results of an efficacy assessment may have little value for the physician whose patients win receive their tests under "usual"' rather than "ideal" conditions. The pragmatist would argue Hat only studies of effectiveness, which attempt to mimic clinical reality, provide the infonnation physicians need to make decisions about individual patients.
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From page 83... ...
Nevertheless, one goal of technology assessment is to foster appropriate changes in practice habits and to discourage the use of additional tests whenever they will not have an impact. In the long teen, if we want to encourage physicians to abandon ineffective tests in favor of more effective ones, we win need to evaluate the technology's substitutive value as wed (Weinstein 1985~.
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From page 84... ...
Sample Size As part of the planning stage, investigators must calculate the sample size required to ensure adequate power for the study. A review of 71 "negative" clinical trials found that 50 of the teals had a greater than 10 percent chance of missing a true 50 percent therapeutic improvement because of small sample sizes (Freiman et al.
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From page 85... ...
The factors that directly influence He size of the sample include heterogeneity of He study population and the degree of accuracy of existing diagnostic methods. Other factors influence the size of the screened population: the frequency of the condition under study, He breadth of the study focus, and the likelihood of patient withdrawal.
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From page 86... ...
For example, "MR! is not a homogeneous diagnostic test, but offers a range of related, but different, diagnostic tests" (Weinstein 1985, p.
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From page 87... ...
study of diagnostic tests for pulmonary embolism took 15 months (Vreim 1988~. Without inshtudonal support, the project cannot succeed.
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From page 88... ...
Referring Physicians The success of the first step, referral, depends on the cooperation of the individuals who usually refer patients for imaging studies: the internist, surgeon, pediatrician, or obstet~cian-gynecologist who requires either a solution to a diagnostic problem or He confirmation of a presumptive diagnosis. Unfortunately, these individuals cannot necessarily be counted on to provide the requisite number of cases (Croke 1979, Marks et al.
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From page 89... ...
Because preliminary studies have suggested Cat MRI has a high level of diagnostic accuracy and the method is now available at many institutions, a physician may feel that it would be unethical to deny He patient an MRI scan · Similarly, in the ideal study designed to compare the accuracy of two diagnostic imaging methods in detecting metastatic disease to the liver, each patient would undergo both of the examinations. How do we convince the referring physician to allow the patient to undergo the second test when the physician is perfectly satisfied with the first examination, which shows He presence or absence of metastases?
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From page 90... ...
When a sample of patients and the general public were surveyed concerning their attitudes about clinical trials, most respondents (71 percent) believed that patients should serge as research subjects and cited the potential benefit to others and the opportunity to increase scientific knowIedge as major reasons.
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From page 91... ...
Summary: Recruitment A primary technology assessment is a form of human experimentation, with all its associated ethical challenges. Lack of interest, informed consent, randomization, and prior judgments of technological superiority may lead to low rates of referral or biased referral and patients who refuse to participate.
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From page 92... ...
The process of random assignment must be carefully specified in Me protocol; it may, for example, involve opening a sequentially numbered, sealed envelope with a code designating the diagnostic procedure to be perfonned. The process must be followed for each study padent.
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From page 93... ...
First, when the study's aim is to define the marginal increment of information Hat a new technology adds in a particular clinical situation, input data may consist of the history, physical examination, and laboratory values that constituted the basis for requesting the examination. Second, background information on each patient is extremely important because the generalizability of a study
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From page 94... ...
The study population may be inadequately characterized, which compromises the generalizability of the study conclusions. Often, studies must rely on busy physicians to provide key clinical data.
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From page 95... ...
Having one person serve as RA means greater standardization of data collection methods. Performing the S - y Tests Success in this phase of data gathering is influenced by many of the same factors Mat affect the quality of He input data Protocol compliance and exam quality are the two most important concems.
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From page 96... ...
Follow-Up Studies An assessment designed to evaluate the impact of a diagnostic test on patient outcome win require clinical foHow-up. In addition, when studies of diagnostic accuracy employ a risky gold standard, patients with negative index tests may not be referred for the gold-standard test, and clinical foBow-up may be used as a substitute.
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From page 97... ...
Some studies of diagnostic accuracy determine the patient's true state by using me gold-standard test in certain patients and clinical follow-up for those who do not undergo the gold-standard test. Follow-up is very
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From page 98... ...
The ideal study would include multiple interpretations of both the index test and the gold standard for the purpose of determining interobserver variability. In a study of effectiveness, tests would be interpreted as they are in usual clinical practice.
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From page 99... ...
Blinded interpretation of the index test and the gold-star~dard test is absolutely essential. Yet most reports of studies of diagnostic tests do not indicate that this precaution has been taken.
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From page 100... ...
a complete description of the sway population, of inclusion and exclusion cr~tena (if used) , and of patients who were rejected or who may have withdrawn fiom the study, so that clinicians can determine how their patients compare to the study population, with particular attention to clinical issues that define He spectrum of sevens of disease; 3.
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From page 101... ...
This occurs when the result of one of the index tests in a comparative study is used to define the true state of the patient. To obtain a valid measure of each test's performance, they must be assessed independently of one another, using a different method to verify the presence or absence of disease.
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From page 102... ...
19861. CONCLUSION In this chapter, we have examined the difficulties encountered in each stage of a primary technology assessment, from the planning and design process Trough the production of the final report.
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From page 103... ...
Recruitment for the National Cooperative Gallstone Study. In Row, H.P., and Gordon, R.S., Jr., eds., Proceedings of me National Conference on Clinical Trials Methodology, October 1977.
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From page 104... ...
In Ro~, H.P., and Gordon, R.S., Ir., eds., Proceedings of ache National Conference on Clinical Trials Methodology, October 1977. Clinical Pharmacology and Therapeutics 25:72~723, 1979.
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From page 105... ...
Controlled Clinical Trials 6:156167, 1985.
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From page 106... ...
Weinstein, M.C. Methodologic considerations in planning clinical trials of cost-effectiveness of magnetic resonance imaging twin a commentary on Guyatt and Dmmmond)
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