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T D Koepsell

Publications and source records attributed to T D Koepsell.

At least 37 records · Page 2Linked to original sources
PubMed2000

Effectiveness of automatic shoulder belt systems in motor vehicle crashes.

CONTEXT: Approximately 10 million cars with automatic shoulder belt systems are currently in use in the United States. However, reports on the effectiveness of such restraints have yielded conflicting results. OBJECTIVE: To determine the effectiveness of automatic shoulder belt systems in reducing the risk of injury and death among front-seat passenger vehicle occupants. DESIGN, SETTING, AND SUBJECTS: Analysis of data collected from the 1993-1996 National Highway Traffic Safety Administration Crashworthiness Data System on front-seat occupants involved in 25,811 tow-away crashes of passenger cars, light trucks, vans, and sport utility vehicles. MAIN OUTCOME MEASURES: Death and serious injury to specific body areas by use of manual lap and shoulder belts, automatic shoulder belts with manual lap belts, or automatic shoulder belts without lap belts, compared with no restraint use. RESULTS: Use of automatic shoulder belts without lap belts was associated with a decrease in the risk of death vs no restraint use but was not statistically significant for all crashes (odds ratio [OR], 0.66; 95% confidence interval [CI], 0.42-1.06) or for frontal crashes (OR, 0.71; 95% CI, 0.38-1.35) after adjustment for occupant age, sex, vehicle year, air-bag deployment, estimated change in vehicle speed during the crash, and principal direction of force. This association was significantly weaker than the 86% lower risk observed for use of automatic shoulder belts with lap belts (OR, 0.14; 95% CI, 0.07-0.26 vs no restraint; P<.05). Use of automatic shoulder belts without lap belts was associated with an increased risk of serious chest (OR, 2.66; 95% CI, 1.11-6.35) and abdominal (OR, 2.06; 95% CI, 1.004-4.22) injuries for all crashes. CONCLUSIONS: These data indicate that improperly used automatic restraint systems may be less effective than properly used systems and are associated with an increased risk of serious chest and abdominal injuries. Given the continued widespread use of these automatic systems, educational programs may be warranted. JAMA. 2000;283:2826-2828

Abdominal Injuries↗
PubMed2000

Effect of a ban on carrying firearms on homicide rates in 2 Colombian cities.

CONTEXT: Homicide is a leading cause of death in Colombia, with much of the fatal interpersonal violence concentrated in the country's largest cities. Firearms are involved in as much as 80% of homicides in Colombia. OBJECTIVE: To evaluate the effect of an intermittent police-enforced ban on carrying firearms on the incidence of homicide in urban Colombia. DESIGN: Interrupted time-series study with multiple replications. SETTING: Cali, Colombia, during 1993 and 1994 and Bogotá, Colombia, from 1995 through August 1997. PARTICIPANTS: The populations of Cali and Bogotá. INTERVENTION: Carrying of firearms was banned on weekends after paydays, on holidays, and on election days. Enforcement included establishment of police checkpoints and searching of individuals during traffic stops and other routine law enforcement activity. MAIN OUTCOME MEASURE: Homicide rates during intervention days were compared with rates during similar days without the intervention; estimates were based on comparisons within the same month, day of week, and time of day. RESULTS: There were 4078 homicides in Cali during 1993 and 1994 (114.6 per 100,000 person-years). In Bogotá, 9106 homicides occurred from 1995 through August 1997 (61 per 100,000 person-years). The incidence of homicide was lower during periods when the firearm-carrying ban was in effect compared with other periods (multivariate-adjusted rate ratio, 0.86 [95% confidence interval [CI], 0.76-0.97] for Cali, and 0.87 [95% CI, 0.77-0.98] for Bogotá). CONCLUSION: An intermittent citywide ban on the carrying of firearms in 2 Colombian cities was associated with a reduction in homicide rates for both cities.

Adolescent↗
PubMed2000

US Department of Veterans Affairs medical care system as a resource to epidemiologists.

Epidemiologists have utilized several health care systems with large numbers of enrollees and centralized databases to achieve their research aims. Although containing many of the features that have made certain health care systems valuable to the conduct of epidemiologic research, the US Department of Veterans Affairs (VA) medical care system has not been well utilized by epidemiologists. This article will describe existing and planned features of this health care system that should be of interest to epidemiologists, including centralized databases that capture hospital discharge and outpatient clinic diagnostic data, a planned enrollment file that would contain all persons eligible for VA medical care, and the size and national dispersion of VA medical care facilities. Also, VA leadership has demonstrated an interest in the promotion of epidemiologic research by initiating several new programs, including the creation of three Epidemiologic Research and Information Centers (ERICs) to foster VA epidemiologic research, and announcing a program to support investigator-initiated epidemiologic research projects with VA funding. Epidemiologists with interests in medical problems that afflict veterans should consider partnerships with VA investigators to achieve their research aims.

Epidemiologic Methods↗
PubMed2000

Apolipoprotein E genotype and the risk of gallbladder disease in pregnancy.

The E4 allele of apolipoprotein E (apoE4) has previously been associated with symptomatic gallstone disease. The aim of this study was to determine if apoE4 is associated with the development of gallbladder sludge and/or stones during pregnancy. We conducted a nested case-control study based on an ongoing cohort study of gallbladder disease in pregnancy. Women in this study receive gallbladder ultrasounds in each trimester of pregnancy. Cases (n = 52) were defined as women with incident gallbladder sludge or stones diagnosed at the third trimester ultrasound. Controls (n = 104) were defined as women without gallbladder sludge or stones on any of 3 study ultrasounds. ApoE genotyping was performed from stored white blood cell pellets. Data were analyzed by stratified analysis and multivariate logistic regression. Cases and controls were similar in baseline characteristics. Forty-two women had sludge, 6 had gallstones, and 4 had both sludge and stones. After adjusting for risk factors such as age, parity, and body mass index, the odds ratio (OR) for the association between heterozygosity or homozygosity for the apoE4 allele and incident gallbladder sludge or stones was 0.91 (95% confidence interval [CI], 0.41-2.02). Further adjustment for family medical history and serum lipid levels did not substantially change these results (OR, 0.73; 95% CI, 0.29-1.82). In conclusion, apoE4 appears to have little or no overall association with the development of new gallbladder sludge or stones in pregnancy. However, an effect could not be ruled out in certain subgroups, such as blacks or women who are homozygous for apoE4.

Apolipoprotein E4↗
PubMed2000

Do physicians judge a study by its cover? An investigation of journal attribution bias.

The effect of a journal's prestige on readers' impressions of an article is unknown. Two hypotheses were tested: first, that attribution of a study to a "high" prestige journal would be associated with improved impressions and attribution to a "low" prestige journal would be associated with diminished impressions; and second, that formal training in epidemiology and biostatistics would mitigate the effects of this journal attribution bias. The study was designed as a trial among a random sample of 264 internists. Participants were asked to read an article and an abstract from either the Southern Medical Journal (SMJ) or the New England Journal of Medicine (NEJM). Questionnaires were constructed that either attributed the article or abstract to its source or presented it as unattributed. After each article or abstract, respondents were asked to rate the quality of the study, the appropriateness of the methodology employed, the significance of the findings, and its likely effects on their practice. A 20-point impression score was created based on responses to these statements. The effect of attribution to a specific journal and formal epidemiology training on impression scores were assessed using linear regression. Of the 399 eligible participants, 264 questionnaires were returned (response rate 66%). Differences in impression scores associated with attribution of an article or abstract to the NEJM were.71 [95% C.I. (-.44-1.87)] and.50 [95% C.I. (-.87-1.87)] respectively; differences in impression scores associated with attribution of an article or abstract to the SMJ were -.12 [95% C.I. (-1.53-1.30)] and -.95 [95% C.I. (-2.41-.52)]. A stratified analysis demonstrated that epidemiology training did not meaningfully alter the effect of journal attribution on participants' impression scores. If journal attribution bias exists, it is likely to exert small and clinically insignificant effects when physicians read articles carefully. Formal training in epidemiology and biostatistics does not appear to alter these results.

Bias↗
PubMed2000

Journal reading habits of internists.

We assessed the reading habits of internists with and without epidemiological training because such information may help guide medical journals as they make changes in how articles are edited and formatted. In a 1998 national self-administered mailed survey of 143 internists with fellowship training in epidemiology and study design and a random sample of 121 internists from the American Medical Association physician master file, we asked about the number of hours spent reading medical journals per week and the percentage of articles for which only the abstract is read. Respondents also were asked which of nine medical journals they subscribe to and read regularly. Of the 399 eligible participants, 264 returned surveys (response rate 66%). Respondents reported spending 4.4 hours per week reading medical journal articles and reported reading only the abstract for 63% of the articles; these findings were similar for internists with and without epidemiology training. Respondents admitted to a reliance on journal editors to provide rigorous and useful information, given the limited time available for critical reading. We conclude that internists, regardless of training in epidemiology, rely heavily on abstracts and prescreening of articles by editors.

Adult↗
PubMed2000

Delivery of primary care to women. Do women's health centers do it better?

OBJECTIVE: Women's health centers have been increasing in number but remain relatively unstudied. We examined patient expectations and quality of care at a hospital-based women's health center compared with those at a general medicine clinic. DESIGN: Cross-sectional survey. SETTING: University hospital-affiliated women's health and general internal medicine clinics. PARTICIPANTS: An age-stratified random sample of 2,000 women over 18 years of age with at least two visits to either clinic in the prior 24 months. We confined the analysis to 706 women respondents who identified themselves as primary care patients of either clinic. MEASUREMENTS AND MAIN RESULTS: Personal characteristics, health care utilization, preferences and expectations for care, receipt of preventive services, and satisfaction with provider and clinic were assessed for all respondents. Patients obtaining care at the general internal medicine clinic were older and had more chronic diseases and functional limitations than patients receiving care at the women's health center. Women's health center users (n = 357) were more likely than general medicine clinic users ( n = 349) to prefer a female provider ( 57% vs 32%, p =.0001) and to have sought care at the clinic because of its focus on women's health (49% vs 17%, p =. 0001). After adjusting for age and self-assessed health status, women's health center users were significantly more likely to report having had mammography (odds ratio [OR] 4.0, 95% confidence interval [CI] 1.1, 15.2) and cholesterol screening (OR 1.6, 95% CI 1.0, 2.6) but significantly less likely to report having undergone flexible sigmoidoscopy (OR 0.5, 95% CI 0.3, 0.9). There were no significant differences between the clinics on receipt of counseling about hormone replacement therapy or receipt of Pap smear, or in satisfaction. CONCLUSIONS: These results suggest that, at least in this setting, women's health centers provide care to younger women and those with fewer chronic medical conditions and may meet a market demand. While the quality of gender-specific preventive care may be modestly better in women's health centers, the quality of general preventive care may be better in general medical clinics.

Adolescent↗
PubMed2000

Intravenous magnesium as an adjuvant in acute bronchospasm: a meta-analysis.

STUDY OBJECTIVE: Although several trials have been published evaluating intravenous magnesium sulfate as treatment for acute bronchospasm, its effectiveness for this indication remains unclear, prompting this meta-analysis. METHODS: All randomized controlled trials of adjuvant bolus intravenous magnesium sulfate for acute bronchospasm in the emergency department were eligible. Trials were identified using MEDLINE, EMBASE, bibliographies of selected articles, and review of abstracts of 4 scientific societies. Two reviewers abstracted data, one of whom was blinded to author and journal. Because studies used different spirometric outcome measures, effect size was calculated for each study by Hedges' method. The analysis used a fixed-effects model. One-way sensitivity analyses were performed to assess the influence of study quality and to search for publication bias. RESULTS: Abstracts from 210 articles were reviewed, yielding 40 trials, of which 9 were specific to bolus intravenous magnesium sulfate in the ED, in doses from 1.2 to 2 g, or an equivalent pediatric dose. Combined results across 9 studies including 859 patients showed a posttreatment effect size of 0.162 for patients treated with intravenous magnesium sulfate (95% confidence interval 0.028, 0.297; P =.02). In sensitivity analyses exploring the effects of study quality and publication bias, the summary effect ranged from 0.127 to 0.206. No serious adverse events were reported. CONCLUSION: Adjuvant bolus intravenous magnesium sulfate in acute bronchospasm appears statistically beneficial in improving spirometric airway function by 16% of a SD. Although the clinical significance of this is uncertain, given the safety of intravenous magnesium sulfate therapy and its relatively low cost, it should be considered, absent contraindications, in patients with moderate to severe acute bronchospasm.

Acute Disease↗
PubMed2000

High school cross country running injuries: a longitudinal study.

OBJECTIVE: To determine the incidence rate of injury among high school cross country runners over a 15-year period. DESIGN: Prospective-longitudinal. SETTING: Twenty-three high schools in western Washington State under the surveillance of the University of Washington Athletic Health Care System between 1979-1994. PARTICIPANTS: One hundred and ninety-nine cross country teams. MAIN OUTCOME MEASURE: Injuries resulting from running in a cross country practice or meet. RESULTS: There were 1,622 injuries for an overall injury rate of 13.1/1,000 athletic exposures (AEs), i.e., participation of a runner in a practice or meet. Girls had a significantly higher overall injury rate (16.7/1,000 AEs) than boys (10.9/1,000 AEs) (p < 0.0001). Girls also had significantly higher injury rates than boys for both initial (p < 0.0001) and subsequent injuries (p < 0.0001), especially those at the same body location (p = 0.0001). This difference in risk estimates was consistent over a 15-year period. Nearly three-fourths of the injuries resulted in < or =4 days of disability. Overall, higher rates of initial injuries were reported during practices (9.2/1,000 AEs) than in meets (7.8/1,000 AEs) (p = 0.04). Shin injuries had the highest overall rates of new injury (1.9/1,000 AEs) and reinjury at the same body location (53.9/1,000 AEs). Girls had significantly higher initial injury rates than boys for shin (p < 0.0001), hip. and foot injuries (p < 0.01), and higher reinjury rates for knee. calf, and foot injuries, respectively (p < 0.05). CONCLUSION: The results of this study suggest that girl cross country runners are at higher risk of injury and reinjury than boy cross country runners.

Adolescent↗
PubMed2000

High-risk periods for childhood injury among siblings.

OBJECTIVE: To determine whether the risk of unintentional injury requiring emergency department (ED) or inpatient care in children is transiently increased over a 90-day period after injury to a sibling. DESIGN: Retrospective cohort. SETTING: King County, Washington. Participants. A total of 41 242 children 0 to 15 years of age continuously enrolled in Medicaid and living in King County during the period October 1, 1992 through September 30, 1993 (27 450 child-years). OUTCOME MEASURES: The outcome was an unintentional injury treated in the ED or inpatient setting. Incidence rates and hazard ratios were calculated for children whose sibling had been injured in the previous 90 days, compared with children without such exposure. Multivariate analysis was used to adjust for age, gender, race, sibling group size, and noninjury ED use. RESULTS: . There were 4921 injuries treated only in the ED and 82 hospital admissions. The incidence of ED treated injury was 305 per 1000 child-years among children whose sibling had been injured in the previous 90 days and 174 per 1000 child-years among children without this exposure (relative risk: 1.75; 95% confidence interval: 1.56-1.95). The incidence of injury-related hospitalization was 1.7 per 1000 child-years among children whose sibling had been injured in the previous 90 days, compared with 3.0 per 1000 child-years among children without this exposure (relative risk:.57; 95% confidence interval:.07-2.12). Injury risk peaked in the period 4 to 10 days after a sibling's injury and returned toward, but did not attain, baseline risk over the subsequent 21/2 months. The magnitude of this effect depended on the child's age; the relative risk of injury was higher among older children. CONCLUSIONS: Injuries treated in the ED or inpatient setting appear to cluster within sibling groups over brief periods of time. Shared social or environmental exposures may contribute to this clustering and may be amenable to targeted, time-limited prevention interventions.

Adolescent↗
PubMed2000

Firearm safety counseling in primary care pediatrics: a randomized, controlled trial.

CONTEXT: Physicians have been encouraged to counsel families about risks associated with gun ownership, but the effectiveness of physician counseling regarding gun safety is unknown. OBJECTIVE: To determine the effectiveness of gun safety counseling during well-child care visits. DESIGN: Group randomized, controlled trial. Physicians, nurse practitioners, and physician assistants were randomized to either the intervention group or a control group. SETTING: Group Health Cooperative, a staff-model health maintenance organization. Patients. Consecutive sample of families (n = 1295) seen for a scheduled appointment for well-child care for a child <18 years of age. Of the families originally scheduled for a visit, 80. 3% were seen and completed the outcomes surveys. INTERVENTION: Each family in the intervention group was given a 60-second message by their practitioner that depended on the presence of guns in the home. Families without guns were informed of the health risks associated with gun ownership and given a standard information pamphlet. Families with guns were given the same information about risks and were told that if they chose to keep a gun, they should store it locked and unloaded. They were given instructions on storage and a folder with material, including the same pamphlet, a letter from the police department, written storage guidelines, and discount coupons for gun storage devices. MAIN OUTCOME MEASURE: Changes in the following self-reported events: 1) acquisition of a safe storage device; 2) removal of firearms from the home; and 3) acquisition of firearms. Results. There were no important differences between intervention and control groups in the rate of acquisition of new guns (intervention: 1.3% vs control:.9%) after the intervention. Among households with guns at baseline, there were also no differences between groups in the removal of guns (intervention: 6.7% vs control: 5.7%), but there was a fairly large nonsignificant difference in the proportion who purchased trigger locks (intervention: 8.0% vs control: 2.5%). CONCLUSIONS: A single firearm safety-counseling session during well-child care, combined with economic incentives to purchase safe storage devices, did not lead to changes in household gun ownership and did not lead to statistically significant overall changes in storage patterns.

Adolescent↗
PubMed2000

The Kaiser Family Foundation Community Health Promotion Grants Program: findings from an outcome evaluation.

OBJECTIVES: To present results from an outcome evaluation of the Henry J. Kaiser Family Foundation's Community Health Promotion Grants Program (CHPGP) in the West, which represented a major community-based initiative designed to promote improved health by changing community norms, environmental conditions, and individual behavior in 11 western communities. METHODS: The evaluation design: 14 randomly assigned intervention and control communities, 4 intervention communities selected on special merit, and 4 matched controls. Data for the outcome evaluation were obtained from surveys, administered every two years at three points in time, of community leaders and representative adults and adolescents, and from specially designed surveys of grocery stores. Outcomes for each of the 11 intervention communities were compared with outcomes in control communities. RESULTS: With the exception of two intervention communities-a largely Hispanic community and a Native American reservation-we found little evidence of positive changes in the outcomes targeted by the 11 intervention communities. The programs that demonstrated positive outcomes targeted dietary behavior and adolescent substance abuse. CONCLUSIONS: Improvement of health through community-based interventions remains a critical public health challenge. The CHPGP, like other prominent community-based initiatives, generally failed to produce measurable changes in the targeted health outcomes. Efforts should focus on developing theories and methods that can improve the design and evaluation of community-based interventions.

Adolescent↗
PubMed1999

A comparison of pain, functional limitations, and work status indices as outcome measures in back pain research.

STUDY DESIGN: We conducted a prospective study with a 2-year follow-up. OBJECTIVE: To compare pain, functional limitations, and work status indices as measures of outcome among back pain patients. SUMMARY OF BACKGROUND DATA: Work status, pain, and functional limitations indices are often considered as interchangeable outcome measures in back pain research. This perspective has been criticized by several authors, who argue that each of these outcome measures reflects a different construct that may vary independently of the others. METHODS: The study was conducted on 720 patients, who sought care for back pain in primary care settings of a large health maintenance organization in 1989-90, and were interviewed one month and two years later. X2 analyses and receiver operating characteristic curves were used to compare the accuracy of a pain rating and a modified 16-item Roland-Morris score in classifying patients on work status and on the change in work status over time. RESULTS: Moderate agreement between the pain and functional limitations measures and work status was observed. Pain and functional limitations change scores agreed moderately with improvement in work status, but were poorly associated with decline in work status. CONCLUSIONS: Although the pain, functional limitations, and work status indices examined in this study are related, they are not equivalent and should not be regarded as interchangeable. These results argue for a clearer distinction of outcome measures in back pain research.

Adult↗
PubMed1999

Trends in the post-hospitalization medical treatment of unstable angina pectoris: 1990 to 1995.

This study provides data on post-hospitalization medication treatment trends for unstable angina between 1990 and 1995. We conducted an observational cohort study at the Veterans Affairs Puget Sound Health Care System (VAPSHCS). Computerized records of hospital discharges and cardiac catheterizations were used to identify unstable angina diagnoses among veterans between 1990 and 1995. Discharge medications issued within 90 days after discharge were ascertained from computerized outpatient pharmacy records. Of the 1,100 veterans discharged with unstable angina, 885 (80%) filled a prescription through the VAPSHCS within 90 days after discharge. Neither use of aspirin nor use of beta blockers increased between 1990 and 1995: overall use averaged 76% for aspirin (78% of those without potential contraindications) and 32% for beta blockers (36% of those without potential contraindications). Use of non-dihydropyridine calcium antagonists--primarily diltiazem--decreased from 57% to 40% (p <0.01), whereas use of dihydropyridine calcium antagonists increased from 12% to 26% (p <0.01). Thus, pharmacy records indicated that aspirin use was high although it was lower than expected, possibly due to ready availability outside the VAPSHCS pharmacy. The low frequency of beta-blocker use and the increasing reliance on dihydropyridine calcium antagonists through 1995 to treat unstable angina may be an opportunity to improve veteran care according to Agency for Health Care Policy Research recommendations.

Adrenergic beta-Antagonists↗
PubMed1999

Increasing response rates for mailed surveys of Medicaid clients and other low-income populations.

Mailing surveys to low-income populations is often avoided because of concern about low response rates. In this study, the authors used a mailed survey of a low-income population to test whether $1.00 or $2.00 cash-response incentives were worth the expense and whether 2-day priority mail ($2.90 postage) would yield a sufficiently higher response rate than certified mail ($1.52 postage) to justify its cost. In 1994, 2,243 randomly selected families in subsidized health care programs in Pierce County, Washington, were randomly sent no incentive, $1.00, or $2.00 in the first of three mailings. For the third mailing, nonrespondents were randomly assigned to receive either certified or 2-day priority mail. After 4 weeks, the response rates were 36.7%, 48.1%, and 50.3% for the no-incentive, $1.00, and $2.00 groups, respectively. After three mailings, the cost per response was the lowest for the group that received $1.00. The response rate for the certified mailing (28.1%) was significantly higher than the rate for the more expensive priority mailing (21.7%). No incentive-related bias was detected. The authors concluded that the most efficient protocol for this low-income population was to use a $1.00 incentive in the first mailing and a certified third mailing.

Aged↗
PubMed1999

Patient-physician racial concordance and the perceived quality and use of health care.

BACKGROUND: Patients from racial and ethnic minority groups use fewer health care services and are less satisfied with their care than patients from the majority white population. These disparities may be attributable in part to racial or cultural differences between patients and their physicians. OBJECTIVE: To determine whether racial concordance between patients and physicians affects patients' satisfaction with and use of health care. METHODS: We analyzed data from the 1994 Commonwealth Fund's Minority Health Survey, a nationwide, telephone survey of noninstitutionalized adults. For the 2201 white, black, and Hispanic respondents who reported having a regular physician, we examined the association between patient-physician racial concordance and patients' ratings of their physicians, satisfaction with health care, reported receipt of preventive care, and reported receipt of needed medical care. RESULTS: Black respondents with black physicians were more likely than those with nonblack physicians to rate their physicians as excellent (adjusted odds ratio [OR], 2.40; 95% confidence interval [CI], 1.55-3.72) and to report receiving preventive care (adjusted OR, 1.74; 95% CI, 1.01-2.98) and all needed medical care (adjusted OR, 2.94; 95% CI, 1.10-7.87) during the previous year. Hispanics with Hispanic physicians were more likely than those with non-Hispanic physicians to be very satisfied with their health care overall (adjusted OR, 1.74; 95% CI, 1.01-2.99). CONCLUSIONS: Our findings confirm the importance of racial and cultural factors in the patient-physician relationship and reaffirm the role of black and Hispanic physicians in caring for black and Hispanic patients. Improving cultural competence among physicians may enhance the quality of health care for minority populations. In the meantime, by reducing the number of underrepresented minorities entering the US physician workforce, the reversal of affirmative action policies may adversely affect the delivery of health care to black and Hispanic Americans.

Adult↗
PubMed1999

Explaining community-level variance in group randomized trials.

Between-community variance or community-by-time variance is one of the key factors driving the cost of conducting group randomized trials, which are often very expensive. We investigated empirically whether between-community variance could be reduced by controlling individual- and/or community-level covariates and identified these covariates from four large community-based group randomized trials or surveys: the Working Well Trial; Kaiser Adolescent Survey; Kaiser Adults Survey; and the Eating Patterns Study. We found that adjusting for covariates will often substantially reduce the between-community variance component. Therefore investigators could block the communities according to these covariates, or adjust for these covariates to improve the power of community trials. We found that the community-by-time variance components are always near zero in these data sets, especially for the surveys where a cohort was followed over time. The covariate adjustment had less impact on reducing the community-by-time variance for the cohort samples than for the cross-sectional samples. This suggests that blocking may not be necessary for the design of the group randomized trials where the change from baseline is of primary interest. The Working Well Trial data were used to illustrate this point.

Adolescent↗