Prevalence, severity, and risk factors for acute exacerbations of nasal and sinus symptoms by chronic rhinosinusitis status.

BACKGROUND: Nasal and sinus symptoms (NSS) are common to many health conditions, including chronic rhinosinusitis (CRS). Few studies have investigated the occurrence and severity of, and risk factors for, acute exacerbations of NSS (AENSS) by CRS status (current, past, or never met European Position Paper on Rhinosinusitis [EPOS] criteria for CRS). METHODS: Four seasonal questionnaires were mailed to a stratified random sample of Geisinger primary care patients. Logistic regression was used to identify individual characteristics associated with AENSS occurrence and severity by CRS status (current long-term, current recent, past, never) using EPOS subjective symptoms-only (EPOSS ) CRS criteria. We operationalized 3 AENSS definitions based on prescribed antibiotics or oral corticosteroids, symptoms, and symptoms with purulence. RESULTS: Baseline and at least 1 follow-up questionnaires were available from 4736 subjects. Self-reported NSS severity with exacerbation was worst in the current long-term CRS group. AENSS was common in all subgroups examined and generally more common among those with current EPOSS CRS. Seasonal prevalence of AENSS differed by AENSS definition and CRS status. Associations of risk factors with AENSS differed by definition, but CRS status, body mass index, asthma, hay fever, sinus surgery history, and winter season consistently predicted AENSS. CONCLUSIONS: In this first longitudinal, population-based study of 3 AENSS definitions, NSS and AENSS were both common, sometimes severe, and differed by EPOSS CRS status. Contrasting associations of risk factors for AENSS by the different definitions suggest a need for a standardized approach to definition of AENSS.

Nasal and sinus symptoms and chronic rhinosinusitis in a population-based sample.

BACKGROUND: The objective of this study was to describe the first US-based study to use the European Position Paper on Rhinosinusitis (EPOS) criteria to study the prevalence of chronic rhinosinusitis (CRS) in a general-population sample. METHODS: A CRS symptom questionnaire was mailed to 23 700 primary care patients from Geisinger Clinic, a health system serving 45 counties in Pennsylvania. CRS cases were categorized into four unique subgroups based on EPOS symptoms: obstruction and discharge with no smell loss or pain/pressure; smell loss without pain/pressure; facial pain and/or pressure without smell loss; and both smell loss and pain/pressure. All cases were required to have nasal obstruction or discharge. Logistic regression was used to evaluate potential factors associated with CRS subgroups. RESULTS: We found that 11.9% of patients met criteria for CRS. Prevalence peaked at 15.9% between ages 50 and 59 years and then dropped to 6.8% after age 69. The odds of CRS was higher among patients who were white, younger, smokers, had a history of Medical Assistance, and had other diseases. When CRS subgroups were modeled separately, these associations were no longer significant for some CRS subgroups. Comorbid diseases were most strongly associated with CRS cases who reported smell loss and facial pain and/or pressure and had the weakest associations with CRS cases who did not report these symptoms. CONCLUSIONS: CRS is a highly prevalent and heterogeneous condition. Differences in risk factors and health outcomes across symptom subgroups may be indicative of differences in etiology that have implications for disease management.

Validation and calibration of HeadCount, a self-report measure for quantifying heading exposure in soccer players.

The long-term effects of repetitive head impacts due to heading are an area of increasing concern, and exposure must be accurately measured; however, the validity of self-report of cumulative soccer heading is not known. In order to validate HeadCount, a 2-week recall questionnaire, the number of player-reported headers was compared to the number of headers observed by trained raters for a men's and a women's collegiate soccer teams during an entire season of competitive play using Spearman's correlations and intraclass correlation coefficients (ICCs), and calibrated using a generalized estimating equation. The average Spearman's rho was 0.85 for men and 0.79 for women. The average ICC was 0.75 in men and 0.38 in women. The calibration analysis demonstrated that men tend to report heading accurately while women tend to overestimate. HeadCount is a valid instrument for tracking heading behaviour, but may have to be calibrated in women.

A population-based study of the epidemiology and clinical features of methicillin-resistant Staphylococcus aureus infection in Pennsylvania, 2001-2010.

No U.S. general population-based study has characterized the epidemiology and risk factors, including skin and soft tissue infection (SSTI), for healthcare-associated (HA) and community-associated (CA) methicillin-resistant Staphylococcus aureus (MRSA). We estimated the incidence of HA- and CA-MRSA and SSTI over a 9-year period using electronic health record data from the Geisinger Clinic in Pennsylvania. MRSA cases were frequency-matched to SSTI cases and controls in a nested case-control analysis. Logistic regression was used to assess risk factors, while accounting for antibiotic administration. We identified 1713 incident CA- and 1506 HA-MRSA cases and 78 216 SSTI cases. On average, from 2005 to 2009, the annual incidence of CA-MRSA increased by 34%, HA-MRSA by 7%, and SSTI by 4%. Age, season, community socioeconomic deprivation, obesity, smoking, previous SSTI, and antibiotic administration were identified as independent risk factors for CA-MRSA.

Construction of a multisite DataLink using electronic health records for the identification, surveillance, prevention, and management of diabetes mellitus: the SUPREME-DM project.

INTRODUCTION: Electronic health record (EHR) data enhance opportunities for conducting surveillance of diabetes. The objective of this study was to identify the number of people with diabetes from a diabetes DataLink developed as part of the SUPREME-DM (SUrveillance, PREvention, and ManagEment of Diabetes Mellitus) project, a consortium of 11 integrated health systems that use comprehensive EHR data for research. METHODS: We identified all members of 11 health care systems who had any enrollment from January 2005 through December 2009. For these members, we searched inpatient and outpatient diagnosis codes, laboratory test results, and pharmaceutical dispensings from January 2000 through December 2009 to create indicator variables that could potentially identify a person with diabetes. Using this information, we estimated the number of people with diabetes and among them, the number of incident cases, defined as indication of diabetes after at least 2 years of continuous health system enrollment. RESULTS: The 11 health systems contributed 15,765,529 unique members, of whom 1,085,947 (6.9%) met 1 or more study criteria for diabetes. The nonstandardized proportion meeting study criteria for diabetes ranged from 4.2% to 12.4% across sites. Most members with diabetes (88%) met multiple criteria. Of the members with diabetes, 428,349 (39.4%) were incident cases. CONCLUSION: The SUPREME-DM DataLink is a unique resource that provides an opportunity to conduct comparative effectiveness research, epidemiologic surveillance including longitudinal analyses, and population-based care management studies of people with diabetes. It also provides a useful data source for pragmatic clinical trials of prevention or treatment interventions.

Patterns of medication use by chronic and episodic headache sufferers in the general population: results from the frequent headache epidemiology study.

Though symptomatic medication overuse is believed to play a role in progression from episodic headaches (EH) to chronic daily headaches (CDH), population-based data on this topic are limited. Our objective was to describe patterns of medication use among CDH and EH sufferers in a general population sample. We compared medications used to treat headache in CDH cases and EH controls identified from a large population-based computer-assisted telephone interview survey. CDH began within 5 years of the computer-assisted telephone interview. Questions on medication use focused on treatment prior to the onset of CDH for cases and on an equivalent period in the past for controls. We asked about the likelihood of treating, time waiting to treat, number of different medications used, first, second and third most frequently used headache pain medication, and total treatment days. Questions were also asked about the use of medication for non-headache pain. Current treatment patterns and past treatment patterns were assessed. Likelihood of use of specific medications was compared between CDH cases and EH controls after adjusting for age, sex, primary headache type and number of medications taken to treat pain. Our sample consists of 206 CDH cases and 507 EH controls. CDH subjects were more likely than EH controls to use over-the-counter/caffeine combination products, triptans, opioid compounds and 'other' prescription pain medications. Use of aspirin was protective. After adjustment, aspirin and ibuprofen were (negatively) associated with CDH [OR = 0.5 (0.3-0.9), OR = 0.7 (0.5-1.0)] and opioids remained positively associated with CDH [OR = 2.3 (1.3-3.9)]. For past use, CDH was positively associated with over-the-counter/caffeine combination products and opioid compounds and was negatively associated with use of aspirin. Only ibuprofen remained (negatively) associated with CDH after adjustment [OR = 0.6 (0.4-0.9)]. After adjusting for demographic factors, primary headache type and number of medications taken, CDH sufferers are more likely to use opioid-combination analgesics, and less likely to use aspirin or ibuprofen, than EH sufferers.

Predictors of variability in urinary incontinence and overactive bladder symptoms.

AIMS: We used data from the General Longitudinal Overactive Bladder Evaluation (GLOBE) to understand predictors of variation in urgency and urinary incontinence (UI) symptoms over time. METHODS: A random sample of Geisinger Clinic primary care patients (men and women) 40+ years of age were recruited for a survey of bladder control symptoms at baseline and 12 months later. Symptom questions used a 4-week recall period. Composite scores were derived for urgency and UI frequency. Logistic regression was used to evaluate predictors of variation in scores at cross-section and longitudinally. RESULTS: A majority of those with UI symptoms and almost 40% of those with urgency symptoms reported episodes of once a week or less often; 17% had symptoms a few times a week or more often. Twenty-one percent with urgency symptoms and 25% with UI symptoms at baseline did not have active symptoms 12 months later. The strongest predictors of active symptoms at follow-up were baseline symptom score and duration of time since first onset of symptoms. Of those with no urgency symptoms at baseline, 22% had urgency at 12 months. Among those with no UI symptoms at baseline, 13% had UI symptoms 12 months later. Among the latter, age (males only) and BMI were the strongest predictors of symptoms at follow-up. CONCLUSIONS: Inter-individual and intra-individual occurrences of urgency and UI symptoms are highly variable in the general population. Use of established predictors to select individuals with less variability in symptoms may help to reduce placebo rates in clinical trials.

Improving detection and treatment of osteoporosis: redesigning care using the electronic medical record and shared medical appointments.

UNLABELLED: To determine whether a process redesign could improve detection and treatment of osteoporosis, at-risk women over the age of 65 were identified using an electronic medical record and proactively contacted by letter and phone call. This resulted in a significant increase in testing for osteoporosis by DXA scan. The high-risk patients were then offered a shared medical appointment, which resulted in improved treatment outcomes compared to usual care. INTRODUCTION: Our objective was to determine if redesigning care through proactive contact with women 65 at-risk of osteoporosis increased BMD testing and to determine if a shared medical appointment (SMA) improved treatment for high-risk women. METHODS: Two primary care sites received the redesign intervention and two other sites served as the usual care controls. At the intervention sites, all women 65 who had not had a DXA scan performed in the prior 2 years were contacted by mail and phone calls. High-risk patients were invited to attend a SMA or follow-up visit with their primary physician. RESULTS: A significantly higher proportion of women at the intervention sites had a DXA (39.6% vs. 13.2%, p < 0.0001). Patients who attended the SMA were more likely to have calcium and vitamin D recommended, a vitamin D level checked, and receive a prescription medicine than those patients who had follow-up with their primary care physician. CONCLUSIONS: The redesigned process was highly effective in improving BMD testing for women 65. The SMA was shown to be a more effective method to make calcium and vitamin D recommendations, to evaluate secondary causes of low bone density, and to prescribe prescription medications, compared to usual care with the PCP.

Cumulative lifetime migraine incidence in women and men.

The aim was to estimate lifetime sex and age-specific incidence of migraine. Data are from the American Migraine Prevalence and Prevention study, a mailed survey sent to 120,000 US households. Age-specific incidence was estimated using self-reported data relevant to identification of migraine cases, age of onset of migraine and age at interview. Migraine incidence peaked between the ages of 20 and 24 years in women (18.2/1000 person-years) and the ages of 15 and 19 years in men (6.2/1000 person-years). Cumulative incidence was 43% in women and 18% in men. Median age of onset was 25 years among women and 24 years among men. Onset in 50% of cases occurred before age 25 and in 75% before age 35 years. Four of every 10 women and two of every 10 men will contract migraine in their lifetime, most before age 35 years. The incidence estimates from this analysis are consistent with those reported in previous longitudinal studies.

Major life changes before and after the onset of chronic daily headache: a population-based study.

Chronic daily headache (CDH), when defined as > or = 15 headache days per month, affects 3-5% of the adult population. Major life changes are putative precipitating events for onset of chronic pain, including chronic headache. This study compared the occurrence of specific life events between CDH cases and episodic headache controls in a community sample. CDH cases (180+ headache days per year: n = 206) and episodic headache controls (2-104 headache days per year: n = 507) were identified from a randomly selected adult US population. Subjects were interviewed about the occurrence of certain major life changes or events (change of residence, employment status, marital status, related to their children, deaths of relatives or close friends, and 'extremely stressful' ongoing situations) occurring in a defined time period. Events that occurred during the same year or year before frequent headache onset in cases or in an equivalent time period in controls were considered to be antecedent events. Those that occurred after this time were considered subsequent events. Compared with episodic headache controls, CDH cases had more major life changes in the year before or same year as CDH onset. After adjusting for age, gender, headache type and year of event, the odds of CDH increased additionally with each antecedent event [odds ratio (OR) 1.20 (1.1, 1.3), P < 0.001], but not with subsequent events [OR 0.94 (0.8, 1.1), P < 0.4]. In secondary analyses, the association between antecedent events and CDH was significant only for the approximately half of CDH cases who were aged >/= 40 years [OR 1.33 (1.2, 1.50) vs. OR 1.04 (0.9, 1.2), P < 0.05 for interaction by age]. These results suggest that major life changes are associated with the onset of chronic daily headache, particularly in middle age.

Elevated blood pressure in primary care varies in relation to circadian and seasonal changes.

Blood pressure (BP) is known to vary by time of day and day of year. Studies differ substantially on the magnitude of the effect and there is doubt whether variation is clinically meaningful. We used more than 2 million BP measurements obtained between 1996 and 2004 from Geisinger Clinic primary care patients. General estimating equations were used to determine the effect of time of day and month of year on the probability of identifying BP values above four diagnostic cutoff points (SBP > or =120 mm Hg, SBP > or =140 mm Hg, DBP > or =80 mm Hg, DBP > or =90 mm Hg). Time of day and month of year were significantly associated with the odds of measuring elevated BP, regardless of definition. The odds ratio (OR) for SBP > or =120 mm Hg in the evening (1900 hours) versus midday (1200 hours) was 1.32 (P < 0.001). The OR for SBP > or =120 mm Hg in winter to summer months was 1.24 (P < 0.001). Similar results were found for each age/gender group. These data indicate that in clinical practice, measurement of an elevated BP may vary by 40% depending on the time of day and month of year. The magnitude of the variability in BP measurement attributable to the combined effect of these temporal factors is clinically significant. Anticipation of changes in BP attributable to temporal factors may improve accuracy of diagnosis and precision of therapy.

Undiagnosed migraine headaches. A comparison of symptom-based and reported physician diagnosis.

BACKGROUND: Although migraine headaches are a common cause of temporary disability, many people with migraine have not been diagnosed. In a sample of the US population, we sought to determine the proportion of migraineurs diagnosed by a physician and to identify the headache characteristics and sociodemographic profiles associated with undiagnosed migraine. METHODS: A mail questionnaire survey was sent to 15,000 US households, selected from a panel to be representative of the US population. Of a total study base population of 23,611, excluding 3043 subjects less than 12 years of age and respondents with unreported gender, we analyzed data for 20,468 subjects aged 12 to 80 years. Migraine diagnoses were assigned on the basis of reported symptoms by means of operational diagnostic criteria. Physician diagnosis of migraine was ascertained on the basis of self-report. RESULTS: Forty-one percent of female and 29% of male migraineurs reported having been diagnosed by a physician. Diagnosis was more likely in females, in people with high income levels, and in individuals who reported migraine associated with aura, vomiting, or disability. Of the undiagnosed subjects, 80% experienced at least some headache-related disability. CONCLUSIONS: Results of this survey indicate that the majority of people with migraine in the United States do not report having been diagnosed by a physician. Given the high proportion of undiagnosed subjects with headache-related disability, efforts to improve the diagnosis and treatment of migraine are recommended.

Efficacy and safety of acetaminophen in the treatment of migraine: results of a randomized, double-blind, placebo-controlled, population-based study.

BACKGROUND: Although most persons with migraine treat their headaches with over-the-counter medication, systematic data on the safety and efficacy of widely used treatment, including acetaminophen, are sparse. METHODS: This is a randomized, double-blind, placebo-controlled study comparing oral acetaminophen, 1000 mg (two 500-mg Extra Strength Tylenol tablets), with identical placebo in the treatment of a single acute migraine attack. Eligible subjects met International Headache Society diagnostic criteria for migraine with or without aura. Patients who usually required bed rest with their headaches or who vomited more than 20% of the time were excluded. MAIN OUTCOME MEASURES: The percentage of subjects who, at 2 hours after dosing, experienced a change in baseline pain intensity from severe or moderate pain to mild or no pain (headache response); and pain intensity difference from baseline at the 2-hour postmedication assessment. RESULTS: The headache response rate 2 hours after dosing was 57.8% in the acetaminophen group and 38.7% in the placebo group (P =.002). Pain-free rates at 2 hours were 22.4% in the acetaminophen group and 11.3% in the placebo group (P =.01). The mean pain intensity difference from baseline 2 hours after dosing was 1.08 in the acetaminophen group and 0.73 in the placebo group (P<.001). At 2 hours, other migraine headache characteristics, such as functional disability (P =.002), photophobia (P =.02), and phonophobia (P =.08), were significantly improved after treatment with acetaminophen vs placebo. CONCLUSIONS: Acetaminophen was highly effective for treating pain, functional disability, photophobia, and phonophobia in a population-based sample of persons with migraine, excluding the most disabled persons with migraine. The drug also had an excellent safety profile and was well tolerated. Arch Intern Med. 2000;160:3486-3492.

Burden of migraine in the United States: disability and economic costs.

BACKGROUND: Migraine is a common disabling disease but its economic burden has not been adequately quantified. OBJECTIVE: To estimate the burden of migraine in the United States with respect to disability and economic costs. METHODS: The following data sources were used: published data, the Baltimore County Migraine Study, MEDSTAT's MarketScan medical claims data set, and statistics from the Census Bureau and the Bureau of Labor Statistics. Disability was expressed as bedridden days. Charges for migraine-related treatment were used as direct cost inputs. The human capital approach was used in the estimation of indirect costs. RESULTS: Migraineurs required 3.8 bed rest days for men and 5.6 days for women each year, resulting in a total of 112 million bedridden days. Migraine costs American employers about $13 billion a year because of missed workdays and impaired work function; close to $8 billion was directly due to missed workdays. Patients of both sexes aged 30 to 49 years incurred higher indirect costs compared with younger or older employed patients. Annual direct medical costs for migraine care were about $1 billion and about $100 was spent per diagnosed patient. Physician office visits accounted for about 60% of all costs; in contrast, emergency department visits contributed less than 1% of the direct costs. CONCLUSIONS: The economic burden of migraine predominantly falls on patients and their employers in the form of bedridden days and lost productivity. Various screening and treatment regimens should be evaluated to identify opportunities to reduce the disease burden.

Headaches preceded by visual aura among adolescents and young adults. A population-based survey.

Clinical descriptions of migraine preceded by visual aura often include a composite of striking and severe symptoms of several attacks in individual patients, but few studies have characterized the spectrum of such attacks. In a population-based telephone survey of 8920 Washington County, Maryland, residents 12 through 29 years old, the attack rate for visual aura headaches during the week prior to the standardized interview was 3.7% in male and 6.1% in female subjects. Among female subjects, the risk for visual aura headache with tension-type symptoms increased with age, whereas the risk for visual aura headache without tension symptoms decreased with increasing age. No clear age-related patterns were observed among male subjects for either type of aura headache. The severity of visual aura headache with and without tension symptoms increased with age among female subjects, but showed an inconsistent pattern among male subjects except for decreasing disability with increasing age. The median interval between the onset of aura symptoms and the onset of headache (aura interval) was 15 minutes in male subjects and 25 minutes in female subjects, with aura intervals longer than 60 minutes reported by 12% of male subjects and 20% of female subjects. In one of the first large population-based studies to characterize the spectrum of visual aura headache, differing age, gender, and subtype patterns were found.

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.

Efficacy and safety of acetaminophen, aspirin, and caffeine in alleviating migraine headache pain: three double-blind, randomized, placebo-controlled trials.

OBJECTIVE: To assess the effectiveness of the nonprescription combination of acetaminophen, aspirin, and caffeine in alleviating migraine headache pain. DESIGN: Three double-blind, randomized, parallel-group, single-dose, placebo-controlled studies. SETTING: Private practice, referral centers, and general community. PATIENTS: Migraineurs with moderate or severe headache pain who met International Headache Society diagnostic criteria for migraine with aura or without aura. The most severely disabled segment of migraineurs, including those whose attacks usually required bed rest, or who vomited 20% or more of the time, were excluded. Of the 1357 enrolled patients, 1250 took study medication and 1220 were included in the efficacy-evaluable data set. INTERVENTION: Two tablets of the nonprescription combination of acetaminophen, aspirin, and caffeine or placebo taken orally as a single-dose treatment of 1 eligible acute migraine attack. MAIN OUTCOME MEASURES: Pain intensity difference from baseline; percentage of patients with pain reduced to mild or none. RESULTS: Significantly greater reductions in migraine headache pain intensity 1 to 6 hours after dose were seen in patients taking the acetaminophen, aspirin, and caffeine combination than in those taking placebo in each of the 3 studies. Pain intensity was reduced to mild or none 2 hours after dose in 59.3% of the 602 drug-treated patients compared with 32.8% of the 618 placebo-treated patients (P< .001; 95% confidence interval [CI], 55%-63% for drug, 29%-37% for placebo); at 6 hours after dose, 79% vs 52%, respectively, had pain reduced to mild or none (P<.001; 95% CI, 75%-82% vs 48%-56%). In addition, by 6 hours after dose, 50.8% of the drug-treated patients were pain free compared with 23.5% of the placebo-treated patients (P<.001; 95% CI, 47%-55% for drug, 20%-27% for placebo). Other migraine headache characteristics, such as nausea, photophobia, phonophobia, and functional disability, were significantly improved 2 to 6 hours after treatment with the acetaminophen, aspirin, and caffeine combination compared with placebo (P< or =.01). CONCLUSIONS: The nonprescription combination of acetaminophen, aspirin, and caffeine was highly effective for the treatment of migraine headache pain as well as for alleviating the nausea, photophobia, phonophobia, and functional disability associated with migraine attacks. This drug combination also has an excellent safety profile and is well tolerated.

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.

Misclassification of genetic susceptibility biomarkers: implications for case-control studies and cross-population comparisons.

Phenotype and genotype markers of genetic susceptibility are of increasing interest in case-control studies of cancer. It is well established that bias to the odds ratio is caused by less-than-perfect assay sensitivity and specificity and varies with risk factor prevalence. As such, the observed variation in odds ratio between studies of genetic markers and cancer risk may be real, or may be attributed, in part, to variation in assay accuracy or in risk factor prevalence (e.g., prevalence differences between racial groups). The latter can be a particular concern when the prevalence of the "at risk" polymorphism in one or more populations is either very high (e.g., > 85%) or very low (e.g., < 15%). For example, even very high sensitivity (e.g., 98%) can produce substantial bias to the odds ratio when the risk factor prevalence is high. Under some prevalence conditions, however, assays with only moderate accuracy are sufficient and result in minimal bias to the odds ratio. Understanding misclassification in the context of marker prevalence may help to explain disparate findings in the literature and should assist investigators in selecting markers that are appropriate for future studies.

Migraine in the United States: a review of epidemiology and health care use.

According to the American Migraine Study, 17.6% of females and 6.0% of males in the United States currently suffer from severe migraine. These findings are based on the responses of more than 20,000 people to a self-administered questionnaire mailed to respondents. The study reveals that migraine prevalence varies according to age, gender, and income. Despite high rates of headache-related disability, the study also shows that most people with migraine have never been diagnosed by a doctor or treated with prescription medications. To improve diagnosis and treatment of migraine, public health interventions are indicated.