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Biomedical subjects

W F Stewart

Publications and source records attributed to W F Stewart.

At least 91 records · Page 5Linked to original sources
PubMed1995

Incorporating biomarkers into cancer epidemiology: a matrix of biomarker and study design categories.

During the last decade, there has been increasing interest in the use of biomarkers in cancer epidemiology to enhance exposure assessment, to gain insight into disease mechanism, and to understand acquired or inherited susceptibility. To facilitate the use of biomarkers in health research, biomarkers have been divided into categories that depict the spectrum of cancer pathogenesis from exposure to disease. In this paper, we consider the epidemiological designs most suitable for the study of each type of marker. In particular, we present a two-dimensional matrix relating the biomarker categories on one axis to four different types of activities (laboratory, transitional, and etiological studies and public health applications) that develop markers and apply them in human populations. We then use the matrix to review the potential application of biomarkers in observational studies of cancer etiology, discussing the advantages, disadvantages, and logistical considerations in using biomarkers to answer research questions.

Biomarkers, Tumor↗
PubMed1994

Prospective study of central nervous system function in amateur boxers in the United States.

Active amateur boxers from six US cities were studied in 1986-1990 to determine whether changes in central nervous system function over a 2-year interval (as evaluated by tests of perceptual/motor function, attention/concentration, psychomotor speed, memory, visuoconstructional ability, and mental control, measures of ataxia and brain-stem auditory evoked potentials, and electroencephalography) were associated with degree of participation in amateur boxing. A total of 484 participants were examined at baseline; 393 (81.2%) were examined 2 years later. At baseline, 22% of the participants had not yet competed in a bout; 9% had never competed in a bout by the second examination. Exposure was defined by number bouts, sparring-years, and sparring with a professional boxer. Very few statistically significant odds ratios were found between exposure and change in function. Significant tests of trend were found between the total number of bouts incurred before the baseline examination and changes in memory, visuoconstructional ability, and perceptual/motor ability. The significant trends for change in function in the latter two domains were primarily due to performance on the Block Design test, which was common to both test domains. No statistically significant associations were found between more recent bouts (after the baseline visit) and any functional domains, nor between bouts or sparring and any other outcome measures. The significant trends with past bouts, but not more recent bouts, may reflect the need for a long latency period before effects are manifest. Alternatively, given changes in safety practices, the observed association may be related to more severe exposure from bouts that occurred before 1986, when new safety measures were imposed.

Adolescent↗
PubMed1994

A validation study of the Dementia Questionnaire.

OBJECTIVE: To determine the validity of the Dementia Questionnaire (a semistructured informant interview) for the diagnosis of dementia. DESIGN: Comparison of dementia status determined by a telephone-administered informant questionnaire with the criterion standard of clinical diagnosis established by examination and laboratory studies. SETTING: Gerontology Research Center, the Baltimore Longitudinal Study of Aging. SUBJECTS: Volunteer cohort of 42 men and 32 women aged 68 to 97 years. Subjects were selected from strata defined by Blessed Information Memory Concentration Test scores, with oversampling of borderline scores (3 to 10). MAIN OUTCOME MEASURES: Sensitivity and specificity of the Dementia Questionnaire in comparison with the criterion standard of clinical diagnosis. SECONDARY OUTCOME MEASURE: Interrater reliability (kappa coefficient). RESULTS: Sensitivity and specificity for dementia were 100% and 90%, respectively. Most false-positive findings were from subjects with cognitive impairment that did not meet criteria for dementia (Diagnostic and Statistical Manual of Mental Disorders, Revised Third Edition. Interrater reliability was high (kappa = 0.83). CONCLUSION: The Dementia Questionnaire can be used effectively in research studies to screen for dementia.

Aged↗
PubMed1994

Occupational case-control studies: I. Collecting information on work histories and work-related exposures.

The strength and credibility of evidence from occupational case-control studies largely depend on the validity and precision with which the work history is reported and the exposure is assessed. We discuss the two steps which ultimately lead to an exposure decision. The first step involves the exchange between the respondent and an interviewer. The latter is usually naïve to occupations and workplace exposures and, as such, is limited to asking generic and open-ended questions about the workplace. Often, this type of information is too nonspecific to assess exposure. In the second step, an expert reviews the information reported on each occupation and decides on exposure status without contacting either the interviewer or respondent. Exposure assessment is not, therefore, integrated with data collection and, in fact, is usually not initiated until after all the interviews are completed. As such, the exposure expert does not have an opportunity to resolve questions before making the exposure decision. To improve the quality and specificity of data collected, we have developed over 40 sets of close-ended questions (branch questions) which are specific to defined occupations. These branch questions, incorporated into a computer-assisted telephone interview, are asked if selected occupations or their synonyms are reported. Second, to link the data collection process with the assessment process, we have developed a procedure called SCORE (Subject Corrected Occupational Report) which provides the industrial hygienist with a cost efficient method to ask questions directly of respondents. Shortly after each interview is completed, a computerized version of the work history is reviewed by the industrial hygienist who develops questions when more information is needed. Subsequently, respondents are mailed a form listing their reported work history along with the questions. After two mailings, 73% of participants in a pilot study returned the SCORE form.

Case-Control Studies↗
PubMed1994

Occupational case-control studies: II. Recommendations for exposure assessment.

Obtaining valid and reliable quantitative exposure estimates is a significant challenge in community-based case-control studies in part, because industrial hygiene monitoring data are usually not available and detailed information on the job and work environment is usually not systematically obtained or assessed. To improve the quality and credibility of disease risk information obtained from occupational case-control studies, we recommend that standardized exposure assessment methods be used to derive quantitative exposure estimates. We identify sources of variation inherent to the assessment process, including: the quality of the information reported on the job, industry, activities, and materials; the industrial hygienist's familiarity with the reported job/industry; the probability that the job/industry was exposed, which depends on plant preferences for particular substances, on process technology, and on customer specifications; and variability in workplace characteristics. To improve the reliability of estimating job-related exposures both within and between studies, we recommend that the epidemiologic analyses be conducted with and without data rated to be of poor quality; that contact be made with experts when the study industrial hygienist is unfamiliar with the manufacturing process in question; that existing data bases be used to estimate the probability of exposure; that a data base be developed that describes manufacturing processes; and that explicit criteria based on industrial hygiene principles be used to evaluate workplace characteristics. In addition, a procedure is described for deriving quantitative exposure estimates by using a reference scale of frequently monitored jobs with their associated mean exposure levels. Areas of research are identified to improve exposure assessment in community-based case-control studies.

Case-Control Studies↗
PubMed1994

Comparative epidemiology of selected midline congenital abnormalities.

We present comparative epidemiologic characteristics of five congenital abnormalities that have been suggested to result from midline abnormal developmental disturbances: esophageal atresia with or without tracheoesophageal fistula (EA/TEF), imperforate anus with or without fistula (IA/F), omphalocele (OM), bladder exstrophy (BE), and diaphragmatic hernia (DH). The purpose was to assess the extent of epidemiologic similarities among these five defects. Data were collected as part of a population-based case-control study of infants with these defects born to mothers residing in Maryland, Washington, D.C., or Northern Virginia from 1980 through 1987. The estimated annual birth prevalences (per 10,000 live births) and 95% confidence intervals (CI) of these five defects were 0.40 (0.26-0.61) for BE, 1.34 (1.08-1.67) for OM, 1.59 (1.29-1.95) for DH, 2.11 (1.76-2.53) for EA/TEF, and 2.97 (2.55-3.46) for IA/F. The birth prevalence of IA/F and DH increased between 1980 and 1987. In contrast to the other four defects, DH showed a significant male preponderance (rate ratio 1.57, 95% CI 1.03-2.47), a significant white excess (rate ratio white:other, 1.56, 95% CI 1.00-2.48), and a lower proportion of multiple associated defects (30% vs. 46-61%). We concluded from this study that the descriptive epidemiology of diaphragmatic hernia is different from that of the other four defects. This finding may imply differences in etiologic and pathogenetic mechanisms underlying DH.

Abnormalities, Multiple↗
PubMed1994

An update on the epidemiology of migraine.

Epidemiologic studies provide estimates of the scope and distribution of the public health problems posed by migraine. These studies have been facilitated by the development of the International Headache Society criteria for migraine, which have now been used in separate prevalence studies in several countries. In this article, we review some of the methodological challenges in studying migraine epidemiology, report recent results from studies using IHS criteria, and suggest directions for future research.

Adolescent↗
PubMed1994

The epidemiology of migraine.

To obtain accurate estimates of migraine prevalence, population-based studies are required. Clinic-based studies include a highly selected group of migraine sufferers. Even in population-based studies, there have been wide variations in estimates of migraine prevalence. A meta-analysis has shown that age, gender and case definition account for 70% of this variance. Recent studies using International Headache Society (IHS) diagnostic criteria have given relatively consistent estimates of migraine prevalence (about 15-18% of women and 6% of men) and indicate that migraine occurs most commonly in men and women aged 25-55 years. Migraine is a heterogeneous condition with a spectrum of severity and associated disability, and it is under-diagnosed worldwide.

Adolescent↗
PubMed1994

The economic and social impact of migraine.

Migraine is an episodic disorder which is often disabling both during and between attacks. While pain intensity is the most important symptom to individual sufferers, headache-related disability is the major determinant of the economic impact of illness. Because migraine is underdiagnosed and under-treated, cost-effective healthcare interventions could serve to reduce the burden of illness on individual sufferers and society. Measures which assess both pain intensity and disability might serve to capture the essential elements of migraine and provide the basis for effective healthcare interventions.

Cost of Illness↗
PubMed1994

Longitudinal study of brainstem auditory evoked responses in 87 normal human subjects.

We evaluated the reproducibility of brainstem auditory evoked responses (BAERs) in 87 normal individuals in a longitudinal study by estimating the correlation coefficients and variability of the interpeak intervals and the V/I amplitude ratio between trials on the same day and between sessions spaced 2 years apart. The highest correlation coefficients occur for the I-V interpeak interval between trials on the same day. The coefficients for the I-III and III-V intervals are lower, due to the variability of wave III. The correlations between ears done on the same day are lower still and are similar to measures obtained from the same ear at a 2-year interval. BAERs are more variable than previously believed between ears and over time, but not in a manner that is clinically significant and can be used longitudinally as a measure of neurologic disease. Finally, we provide the sample size required to detect a significant change in interpeak intervals.

Acoustic Stimulation↗
PubMed1994

The burden of migraine. A review of cost to society.

Migraine is a common episodic disorder with considerable impact on individuals and society. Migraine occurs with the highest prevalence between the ages of 25 and 55 years, potentially the most productive period of life. Severe migraine can lead to disruption of work, family and social life, the long term consequences of which may affect quality of life. The direct costs of migraine (due to medical care) are small compared with the indirect costs caused by absence from work and reduced productivity. Population-based studies are required to assess incidence, prevalence and distribution of the disease. These studies also reveal that migraine is currently underdiagnosed and undertreated. The cumulative impact of migraine on individuals produces the burden of illness on society. Measuring the severity of migraine is important in understanding the extent of the burden of migraine on the individual and on society. Measures of severity may be useful as predictors of disability and healthcare use. These measures may also be useful in assessing the need for patient care and treatment and help target those more disabled by migraine. Identifying and treating appropriate patients should reduce the impact of migraine on the individual and the burden of migraine on society.

Age Factors↗
PubMed1994

Migraine prevalence. A review of population-based studies.

Obtaining accurate and reliable information on the prevalence of migraine is essential to understanding the burden it places on society. Although the epidemiology of headache has been described in more than 50 population-based studies, only 24 of these have described the gender- and age-specific prevalence of migraine. Essentially five different case definitions have been used in these studies. Variation in the prevalence of migraine among studies is largely due to differences in case definition and in the age and gender distribution of study populations. Among four recent studies that used the diagnostic criteria of the International Headache Society (IHS), a coherent picture emerges. The prevalence of migraine is approximately 6% among men and 15 to 17% among women. Prevalence varies by age, increasing to about age 40 years and declining thereafter in both men and women. The gender ratio also appears to vary by age, increasing from menarche to about age 42 years and declining thereafter. Although the use of the IHS criteria has resulted in a more coherent picture across population-based studies, efforts must be made to assess the reliability and validity of these criteria in population-based samples.

Adolescent↗
PubMed1994

Migraine heterogeneity. Disability, pain intensity, and attack frequency and duration.

Data from population-based studies are summarized to characterize the full range and variability of the impact migraine has on the individual. Despite differences in methods and data collection in population-based studies describing disability, pain intensity, and attack frequency as well as the duration of migraine and other headaches, several patterns emerge. On average, migraine headaches are more disabling, more painful, and longer in duration than other types of headaches. Females report more pain and disability with headache than do males. Although disability measurements are important in demonstrating the effect of headache on both the individual and society, actual measurements often fall short. Most studies use only workdays lost as the sole measure of disability. Most migraineurs do not miss work while experiencing a headache; instead, they attempt to function on the job, with considerably reduced effectiveness. Computing only workdays lost does not account for impairment at work nor does it show the impact of migraine on other aspects of life. In addition, evidence suggests the presence of a pain intensity threshold for disability. Headache-related pain intensity below the threshold is not associated with disability. Despite the threshold of pain intensity for disability, a significant proportion of migraine sufferers report levels of pain intensity above the threshold in the absence of work-related disability. The grading of headache severity should be a composite that would permit a more complete image of the heterogeneity of migraine's effects and a more accurate idea of the need for healthcare services. This composite should include two areas: (1) more complete measures of life impact, encompassing daily activities in a number of domains, including work, family, and social activities; and (2) an assessment of pain intensity and attack frequency.

Adolescent↗
PubMed1994

Assessing headache severity. New directions.

Headache is a heterogeneous condition that varies widely in global severity and in severity of individual attacks. Whereas recent efforts have focused on improving the diagnostic criteria for classifying headache, less effort has been directed toward developing reliable, valid, and clinically useful methods of assessing the impact or severity of headache. Existing measures of severity include one or more of the following weaknesses: (1) only pain intensity is assessed or the measure is incomplete in other ways, (2) measures have little or no prognostic value for relevant outcomes, (3) the reliability or the validity of the measure has not been assessed, or (4) the measure is too cumbersome for clinical practice or field research. We describe a brief, simple method for grading the severity of headache, the Chronic Pain Index, which assumes that a continuum of pain intensity and disability is the underlying dimension of severity. Along this continuum, lower levels of severity are differentiated by pain intensity and higher levels by interference with function. The prognostic value of the results from a seven-item questionnaire for grading headache severity is compared with that of alternative measures. The Chronic Pain Index showed the strongest independent cross-sectional and prospective correlation with measures of headache impact, depression, and use of healthcare services. These results support the potential utility of brief methods of assessing headache severity and exemplify the importance of including measures of interference with function when assessing severity.

Headache↗