Differences In Prevalence Estimates Research Articles

Assessment of Bias in National Growth-monitoring Data: A Case Study in Zimbabwe

This study assesses the extent to which children under five years of age attending a growth-monitoring program are representative of the population as a whole. Bias in the prevalence of underweight estimated through growth-monitoring is assessed by comparing data from the program with prevalence estimates from the community-based Demographic and Health Surveys of 1988 and 1994. Geographic patterns of attendance at growth-monitoring are also examined through a comparison with census data, and trends in growth-monitoring data are also assessed. Provincial and national estimates of the prevalence of underweight from the two sources were not significantly different in 1988, but significant differences in prevalence estimates were identified in 1994. This suggests that growth-monitoring attendees were less representative of the general population in 1994 than at the start of the study period. The methodology used is transferable elsewhere, since the same data sets exist for many other African countries.

Prevalence of mental retardation and developmental disabilities: estimates from the 1994/1995 national health interview survey disability supplements.

In 1994 and 1995, the National Health Interview Survey included a Disability Supplement (NHIS-D) to collect extensive information about disabilities among individuals sampled as part of annual census-based household interview surveys. Here we describe the development and application of operational definitions of mental retardation and developmental disabilities to items in the NHIS-D to estimate prevalence. In our analyses, we estimate the prevalence of mental retardation in the noninstitutionalized population of the United States to be 7.8 people per thousand (.78%); of developmental disabilities, 11.3 people per thousand (1.13%); and the combined prevalence of mental retardation and/or developmental disabilities to be 14.9 per thousand (1.49%). Differences in prevalence estimates for mental retardation and developmental disabilities and among people of various ages are explored.

Adolescent Sexual Behavior: Estimates and Trends from Four Nationally Representative Surveys

Accurate information about trends over time in adolescent sexual behavior is essential to understand changes in adolescent pregnancy and sexually transmitted diseases and to monitor the progress of health promotion activities in the United States Estimates from the National Survey of Family Growth (NSFG), the National Survey of Adolescent Males (NSAM), the Youth Risk Behavior Survey (YRBS) and the National Longitudinal Study of Adolescent Health (Add Health) were compared. While methodologies and populations varied by survey, adolescents aged 15-17 who attend high school were a common subpopulation among all four. For each survey, the prevalence of sexual intercourse, contraceptive use and multiple sexual partners was measured in this population. Trend comparisons fell into four categories. First, some similar significant trends were found across surveys. The proportion of all males and of white males who reported ever having had sexual intercourse decreased significantly, while condom use rose significantly among males in both the NSAM and the YRBS. For such behaviors as ever having had sexual intercourse (among Hispanic males and black females), using the pill and using the condom (among all females) and having four or more lifetime sexual partners (among white males), a significant trend was found in one survey while a similar but nonsignificant trend was found in another. Several trend comparisons were not significant in any survey. Finally, having had intercourse in the past three months (among all males and all females), having had two or more partners in the past three months (for males) and having had four or more lifetime sexual partners (among white females and all males) showed a significant trend in one survey but lacked a parallel nonsignificant trend in another. Prevalence estimates in 1995 differed significantly in at least one comparison of surveys for all behaviors except having four or more lifetime sexual partners (both genders) and having two or more recent sexual partners (females). Gender differences within the YRBS and between the NSFG and the NSAM generally were consistent. Trends over time and gender differences were similar across surveys, underscoring their value for tracking adolescent sexual behaviors. Differences in prevalence estimates across surveys probably result from differences in question wording, diverse interview settings and modes of data collection, and varying statistical power. These findings suggest a need to increase our understanding of how methodologies influence survey response in research on adolescents.

The effect of screening on prevalence estimates of alcohol dependence and social consequences.

Screener items are often used in surveys to identify individuals who are at high risk of experiencing alcohol dependence or alcohol-related problems. The purpose of this study is to determine the effect of two screener items (5 or more drinks ever and > or = 12 drinks last year) on prevalence estimates of alcohol dependence and negative social consequences. The 1995 National Alcohol Survey data were analyzed. Differences in prevalence estimates between the unscreened current drinkers (n = 2,817) and the two screened samples: 5+ ever (n = 2,186) and > or = 12 drinks last year (n = 2,126) were compared. For each screened sample, prevalence estimates obtained from two base populations (screened positives only and all current drinkers assuming no alcohol-related problems among screened negatives) were examined. Comparisons of prevalence estimates of alcohol dependence and negative social consequences across the screened and unscreened samples revealed little bias in estimates with one exception. The only significant difference between the unscreened and screened samples was found among women when prevalence rates were obtained from data of screened positive respondents only. The effect of screening on national prevalence estimates of alcohol dependence and social consequences is small. Less bias in prevalence estimates is found when negatively screened light drinkers were assumed to report no alcohol-related problems rather than excluded from the estimation sample.

Comparison of fecal samples collected per rectum and off the ground for estimation of environmental contamination attributable to beef cattle

Abstract Objectives To determine whether sampling feces off the ground replicates prevalence estimates for specific pathogens obtained from fecal samples collected per rectum of adult cows, and to determine characteristics of feces on the ground (fecal pats) that are associated with subsequent identification of Campylobacter spp, Cryptosporidium parvum, and Giardia duodenalis. Animals A random sample of adult beef cattle from 25 herds located throughout California. Procedure 1,115 rectal and ground fecal samples were obtained. Samples were submitted for culture of Campylobacter spp and examined, using a direct fluorescent antibody assay, to detect C parvum oocysts and G duodenalis cysts. Characteristics of fecal pats, such as volume and consistency, were recorded. Results Prevalence of Campylobacter spp was 5.0% (20/401) for rectal fecal samples, which was significantly greater than prevalence determined for ground fecal samples (2/402; 0.5%). Most isolates were C jejuni subsp jejuni. Prevalence of C parvum was higher in rectal fecal samples (6/557; 1.1%) than in ground fecal samples (1/558; 0.2%), but this difference was not significant. Prevalence of G duodenalis did not differ for rectal (36/557; 6.5%) versus ground (26/558; 4.7%) fecal samples. Conclusions and Clinical Relevance Evaluation of ground fecal samples may not accurately indicate the prevalence of Campylobacter spp or C parvum in cattle but may reflect prevalence of G duodenalis Differences in prevalence estimates between the 2 methods suggest inactivation of pathogens in feces after cattle have defecated. Prevalence estimates generated by evaluation of ground fecal samples, however, may more accurately estimate environmental pathogen burden. (Am J Vet Res 1999;60:1352–1356)

Estimating the prevalence of delayed median nerve conduction in the general population.

The objectives of this study were to determine the point prevalence of neurophysiologically defined median nerve compression and associated carpal tunnel syndrome in a random sample of the general population. The design was a two-stage screening study: (i) a cross-sectional survey to estimate the point prevalence of current hand symptoms; (ii) nerve conduction testing of the median nerve in weighted samples of the survey respondents. The target study population was a random sample of 1000 adults aged between 18 and 75 yr registered with a family practice in the UK. A mailed questionnaire enquired about hand symptoms on the day and included various demographic questions. Weighted random samples were taken based on the hand symptoms reported, and the subjects were invited to attend for motor and sensory median nerve conduction testing. A neurophysiological diagnosis of median nerve compression was made based on a number of different cut-offs using published criteria. Of those receiving a questionnaire, 79% responded. A total of 250 responders were invited to attend for nerve conduction testing, of whom 155 (62%) attended. Non-response to the questionnaire and non-attendance for nerve conduction testing may have biased the prevalence estimates. After adjustment for such biases, a prevalence estimate of between 7 and 16% was obtained, varying with the different cut-offs used to define delayed median nerve conduction. Subjects over 54 yr of age had a higher prevalence than younger participants. There was no difference in prevalence estimates between men and women. The conclusion reached was that carpal tunnel syndrome, as assessed by delayed median nerve conduction, is common in the general population.

The Prevalence of Chronic Fatiguing Illnesses Among Adolescents in the United States

Objective. To compare the prevalence of unexplained chronic fatigue (CF) and chronic fatigue syndrome (CFS) among adolescents in three studies conducted by the Centers for Disease Control and Prevention and to compare these estimates with those for adults in two of the studies.Design. The studies used the following three designs: (i) a physician-based CFS surveillance system, (ii) a random, cross-sectional community telephone survey and (iii) a cross-sectional survey of school nurses.Setting. Surveillance included all patients with unexplained fatigue seen by participating physicians in four communities over a 2-year period; the community survey was conducted in a defined, urban population; and the survey of nurses included all middle, junior, and high school nurses in two communities.Patients or other participants. Twenty-three adolescent cases of unexplained chronic fatiguing illness were reported to the surveillance system, 7 of whom were classified with CFS. The community survey screened 2,249 persons between the ages of 2 and 17 years and identified 5 with unexplained chronic fatiguing illness, only one of whom might have had CFS. The school nurses identified 22 students with unexplained fatiguing illness, 10 of whom had received a diagnosis of CFS.Main outcome measures. The prevalence of unexplained chronic fatiguing illness was estimated in all three studies. The prevalence of CFS was estimated in one study, the prevalence of CFS-like illness was estimated in another, and the prevalence of a reported diagnosis of CFS was estimated in the third.Results. In general, the prevalence estimates of CF, CFS-like illness, and CFS for adolescents were lower than those for adults. One study also included children ages 2 to 11 years and found very little CF and no CFS. Cases of CFS among adolescents were evenly distributed across individual years of age.Conclusions. CFS was clearly present among adolescents, although the prevalence for this group was lower than for most adult age groups. Differences in prevalence estimates among the three studies were consistent with differences in study designs. The validity of adolescent/adult comparisons within each study should not be affected by the study design. Further study of the applicability of the current CFS case definition to adolescents is warranted.

Population variation in migraine prevalence: A meta-analysis

A meta-analysis of published studies was conducted to identify factors which explained variation in estimates of migraine prevalence. Twenty-four population based studies contributed a total of 168 gender and age specific estimates of migraine prevalence. In linear regression analysis, 70.6% of the variation in these prevalence estimates was explained by gender, age (AGE + AGE 2), a binary variable for case definition, and an interaction term between age and the case definition. Initially, we identified five groups of case definitions among the 24 studies. Only the definition of Waters (any 2 of warning, nausea, or unilateral pain) was associated with statistically significant differences in prevalence estimates among studies; accordingly the other 4 groups were combined. Several other factors were examined as predictors of migraine prevalence including the method of selecting the study population, the source of the population, the response rate and whether diagnoses were confirmed by a clinical assessment. None of these factors substantially increased explained variance. We conclude that after taking sociodemographic factors and case definition into account, estimates of migraine prevalence are remarkably stable among studies.

Evaluation of a self-administered questionnaire on hand dermatitis.

The purpose of the study was to evaluate a self-administered questionnaire on hand dermatitis that was developed to identify persons with hand dermatitis in epidemiological studies. A total of 109 nurses were subject to dermatological examination of the hands within 1 month of returning the questionnaire. 2 types of questionnaire diagnoses were made: a 'symptom-based' diagnosis and a 'self-reported diagnosis'. These were compared to the medical diagnosis of hand dermatitis. The prevalence of hand dermatitis in the 12 months before the study, based on the medical diagnosis, was 18.3%. The prevalence according to the symptom-based diagnosis and the self-reported diagnosis was 47.7% and 17.4%, respectively. The sensitivity and specificity of the symptom-based diagnosis were 100% and 64%, respectively. It is concluded that the symptom-based diagnosis can be used as screening instrument for the detection of cases in large study populations, if followed by dermatological examination of persons with a positive diagnosis. The sensitivity and specificity of the self-reported diagnosis were 65% and 93%, respectively. It is concluded that the self-reported diagnosis can be used to obtain a rough estimate of the prevalence, although comparison of prevalence figures between study populations may be distorted due to a difference in reporting of hand dermatitis. The results of the study illustrate the size of the differences in prevalence estimates that may arise as a result of differences in the definition and method of diagnosing hand dermatitis.

Allgemeinärzte und Internisten verschreiben Psychopharmaka

An epidemiological study using data from a local German health insurance fund on the psychotropic drug prescription of physicians and the drug utilisation of their patients is presented. Taking a sample of 280 out-patients, descriptive methods are presented (defined daily dose (DDD), prescribed daily dose (PDD), active-agent-oriented classification of drugs, therapy-oriented classification of diagnoses). The following questions are answered by this study: Which patients with which indication received which dosage of which psychotropic drug for how long from which physicians? The patient-based structure of the data, taking into account the prescriptions of all physicians allows the course of therapies and the study of overall psychotropic medication. Prevalences estimates concerning the patients are also possible. Our results are compared with those of similar pharmaco-epidemiological studies; the difference in prevalence estimates, as well as advantages and possible disadvantages arising from the use of such secondary data base, are discussed.

Common sense epidemiology: self-based judgments from laypersons and physicians.

This article reports two studies on a neglected aspect of common sense epidemiology: subjective estimates of the prevalence of symptoms and diseases. Based on social-psychological research on the false-consensus effect, it was hypothesized that subjects who had a history of a condition would estimate its prevalence to be greater than would subjects who did not have a history of that condition. This hypothesis was supported across several different symptoms and diseases. Expertise did not confer protection from the effect. It occurred among 110 college students in Study 1 as well as among 65 practicing physicians in Study 2. In addition, college students who estimated the prevalence of a condition as relatively high rated that condition as less life-threatening than did other students, and students who had a history of a condition rated it as less life-threatening than did their counterparts without such a history. The discussion focuses on (a) explanations of differences in prevalence estimates as a function of personal health history, (b) implications for laypersons' judgments of seriousness, their emotional reactions to illness threats, and their illness behavior, and (c) implications for physicians' diagnostic behavior.