Background. The study purpose was to establish the number (and type) of days needed to estimate mean pedometer-determined steps/day in a field setting.
Methods. Seven days of data were collected from ...90 participants (33 males, age = 49.1 ± 16.2 years, BMI = 27.2 ± 4.1 kg/m
2; 57 females, age = 44.8 ± 16.9 years, BMI = 27.0 ± 5.9 kg/m
2). Mean steps/day were computed for all 7 days (the criterion), each single day, and combinations of days. Analyses included repeated measures ANOVA, intra-class correlations (ICC), and regression.
Results. There was a significant difference (
P < 0.001) between days. The difference was limited to Sunday and accounted for 5% of the variance. ICC analyses indicated a minimum of 3 days is necessary to achieve a reliability of 0.80. The adjusted
R
2 was 0.79 for a single day (specifically Wednesday), 0.89 for 2 days (Wednesday, Thursday), and 0.94 for 3 days (Wednesday, Thursday, Friday). Sunday was the last day to enter the model.
Conclusions. Although there is a statistical difference between days, there is little practical difference, and the primary distinction appears limited to Sunday. Although a single day of collection is not acceptable, any 3 days can provide a sufficient estimate.
Frailty models are generally used to model heterogeneity between the individuals. The distribution of the frailty variable is often assumed to be continuous. However, there are situations where a ...discretely-distributed frailty may be appropriate. In this paper, we propose extending the proportional hazards frailty models to allow a discrete distribution for the frailty variable. Having zero frailty can be interpreted as being immune or cured (long-term survivors). Thus, we develop a new survival model induced by discrete frailty with zero-inflated power series distribution, which can account for overdispersion. A numerical study is carried out under the scenario that the baseline distribution follows an exponential distribution, however this assumption can be easily relaxed and some other distributions can be considered. Moreover, this proposal allows for a more realistic description of the non-risk individuals, since individuals cured due to intrinsic factors (immune) are modeled by a deterministic fraction of zero-risk while those cured due to an intervention are modeled by a random fraction. Inference is developed by the maximum likelihood method for the estimation of the model parameters. A simulation study is performed in order to evaluate the performance of the proposed inferential method. Finally, the proposed model is applied to a data set on malignant cutaneous melanoma to illustrate the methodology.
In this article, we propose an alternative gap time model based on a multiplicative marginal rate function, which is formulated considering each gap time conditional on the previous recurrence times. ...In this formulation, the gap times are treated equally and the relation between successive events is no longer a problem. Furthermore, this article considers the inclusion of a proportion of zero-recurrence units (for which the event of interest will not occur) into the model to analyze recurrent event data. Inference aspects of the proposed model are discussed through maximum likelihood approach. A simulation study is carried out to examine the performance of the estimation procedure. The model is applied to hospital readmission data among colorectal cancer patients.
Background: Exercise is an important component of pulmonary rehabilitation for patients with chronic lung disease. Objective: To explore the role of physical activity in maintaining cardiac and ...respiratory function in healthy people. Methods: Cardiorespiratory fitness was measured by a maximal treadmill test (MTT), and respiratory function was tested by spirometry. The cross sectional study included data from 24 536 healthy persons who were examined at the Cooper Clinic between 1971 and 1995; the longitudinal study included data from 5707 healthy persons who had an initial visit between 1971 and 1995 and a subsequent visit during the next five years. All participants were aged 25–55 years and completed a cardiorespiratory test and a medical questionnaire. Results: In the cross sectional study, after controlling for covariates, being active and not being a recent smoker were associated with better cardiorespiratory fitness and respiratory function in both men and women. In the follow up study, persons who remained or became active had better MTT than persons who remained or became sedentary. Men who remained active had higher forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) than the other groups. Smoking was related to lower cardiorespiratory fitness and respiratory function. Conclusions: Physical activity and non-smoking or smoking cessation is associated with maintenance of cardiorespiratory fitness. Change in physical activity habits is associated with change in cardiorespiratory fitness, but respiratory function contributed little to this association during a five year follow up.
The purpose was to describe current levels of physical activity and inactivity among adults and young people in the United States.
Estimates of participation in regular physical activity were derived ...from three national surveys for adults (National Health Interview Survey, National Health and Nutrition Examination Survey, and the Behavioral Risk Factor Surveillance System) and from the Youth Risk Behavior Survey for high school students.
Overall, 63.8% of high school students surveyed on the 1997 YRBS reported participating in vigorous physical activity for at least 20 min on 3 or more days per week. Participation in vigorous activity was higher for boys (72.3%) than girls (53.5%), whites (66.8%) compared with blacks (53.9%) and Hispanics (60.4%), and decreased with advancing grade. Among adults, 27.7% meet recommended levels of either moderate or vigorous physical activity, whereas 29.2% report no regular physical activity outside of their work. Gender differences in participation in physical activity are less pronounced than in youth, and age-related patterns were complex. Whites are more active than blacks and Hispanics, and persons with higher family incomes and more education report being more physically active. There have been only minor changes in reported participation in leisure time physical activity over the past 15 yr.
National estimates of physical activity appear to be reliable and valid for adults but may be less so for adolescents and are poor measures for children. Research is needed to determine the role that objective monitoring with accelerometers may play in surveillance. Reliable and valid measures of occupational, household, and transportation-related physical activity and sedentary behaviors are needed to better characterize the range of activity that is associated with health.
In 1995 the American College of Sports Medicine and the Centers for Disease Control and Prevention published national guidelines on Physical Activity and Public Health. The Committee on Exercise and ...Cardiac Rehabilitation of the American Heart Association endorsed and supported these recommendations. The purpose of the present report is to update and clarify the 1995 recommendations on the types and amounts of physical activity needed by healthy adults to improve and maintain health. Development of this document was by an expert panel of scientists, including physicians, epidemiologists, exercise scientists, and public health specialists. This panel reviewed advances in pertinent physiologic, epidemiologic, and clinical scientific data, including primary research articles and reviews published since the original recommendation was issued in 1995. Issues considered by the panel included new scientific evidence relating physical activity to health, physical activity recommendations by various organizations in the interim, and communications issues. Key points related to updating the physical activity recommendation were outlined and writing groups were formed. A draft manuscript was prepared and circulated for review to the expert panel as well as to outside experts. Comments were integrated into the final recommendation.
To promote and maintain health, all healthy adults aged 18 to 65 yr need moderate-intensity aerobic (endurance) physical activity for a minimum of 30 min on five days each week or vigorous-intensity aerobic physical activity for a minimum of 20 min on three days each week. I (A) Combinations of moderate- and vigorous-intensity activity can be performed to meet this recommendation. IIa (B) For example, a person can meet the recommendation by walking briskly for 30 min twice during the week and then jogging for 20 min on two other days. Moderate-intensity aerobic activity, which is generally equivalent to a brisk walk and noticeably accelerates the heart rate, can be accumulated toward the 30-min minimum by performing bouts each lasting 10 or more minutes. I (B) Vigorous-intensity activity is exemplified by jogging, and causes rapid breathing and a substantial increase in heart rate. In addition, every adult should perform activities that maintain or increase muscular strength and endurance a minimum of two days each week. IIa (A) Because of the dose-response relation between physical activity and health, persons who wish to further improve their personal fitness, reduce their risk for chronic diseases and disabilities or prevent unhealthy weight gain may benefit by exceeding the minimum recommended amounts of physical activity. I (A).
Three methods for measuring time spent in daily physical activity (PA) were compared during a 21-d period among 83 adults (38 men and 45 women).
Each day, participants wore a Computer Science and ...Applications, Inc. (CSA) monitor and completed a 1-page, 48-item PA log that reflected time spent in household, occupational, transportation, sport, conditioning, and leisure activities. Once a week, participants also completed a telephone survey to identify the number of minutes spent each week in nonoccupational walking and in moderate intensity and hard/very hard-intensity PA. Data were analyzed using descriptive statistics and Spearman rank-order correlations. Three equations developed to compute CSA cut points for moderate and hard/very hard PA were also compared with the PA logs and PA survey.
There was modest to good agreement for the time spent in different PA intensity categories between the three CSA cut point methods (r = 0.43-0.94, P < 0.001). Correlations between the CSA and PA logs ranged from r = 0.22 to r = 0.36, depending on the comparisons. Correlations between the survey items and PA logs were r = 0.26-0.54 (P < 0.01) for moderate and walking activities and r < 0.09 (P > 0.05) for hard/very hard activities. Correlations between the survey items and the CSA min per day varied according to the method used to compute the CSA intensity cut points.
The results were consistent with findings from other PA validation studies that show motion sensors, PA logs, and surveys reflect PA; however, these methods do not always provide similar estimates of the time spent in resting/light, moderate, or hard/very hard PA.
In this paper, we introduce a new model for recurrent event data characterized by a baseline rate function fully parametric, which is based on the exponential‐Poisson distribution. The model arises ...from a latent competing risk scenario, in the sense that there is no information about which cause was responsible for the event occurrence. Then, the time of each recurrence is given by the minimum lifetime value among all latent causes. The new model has a particular case, which is the classical homogeneous Poisson process. The properties of the proposed model are discussed, including its hazard rate function, survival function, and ordinary moments. The inferential procedure is based on the maximum likelihood approach. We consider an important issue of model selection between the proposed model and its particular case by the likelihood ratio test and score test. Goodness of fit of the recurrent event models is assessed using Cox‐Snell residuals. A simulation study evaluates the performance of the estimation procedure in the presence of a small and moderate sample sizes. Applications on two real data sets are provided to illustrate the proposed methodology. One of them, first analyzed by our team of researchers, considers the data concerning the recurrence of malaria, which is an infectious disease caused by a protozoan parasite that infects red blood cells.
This paper presents a new parametric model for recurrent events, in which the time of each recurrence is associated to one or multiple latent causes and no information is provided about the ...responsible cause for the event. This model is characterized by a rate function and it is based on the Poisson-exponential distribution, namely the distribution of the maximum among a random number (truncated Poisson distributed) of exponential times. The time of each recurrence is then given by the maximum lifetime value among all latent causes. Inference is based on a maximum likelihood approach. A simulation study is performed in order to observe the frequentist properties of the estimation procedure for small and moderate sample sizes. We also investigated likelihood-based tests procedures. A real example from a gastroenterology study concerning small bowel motility during fasting state is used to illustrate the methodology. Finally, we apply the proposed model to a real data set and compare it with the classical Homogeneous Poisson model, which is a particular case.
State-level statistics of adherence to the physical activity objectives in Healthy People 2010 are derived from the Behavioral Risk Factor Surveillance System (BRFSS) data. BRFSS physical activity ...questions were updated in 2001 to include domains of leisure time, household, and transportation-related activity of moderate- and vigorous intensity, and walking questions. This article reports the reliability and validity of these questions.
The BRFSS Physical Activity Study (BPAS) was conducted from September 2000 to May 2001 in Columbia, SC. Sixty participants were followed for 22 d; they answered the physical activity questions three times via telephone, wore a pedometer and accelerometer, and completed a daily physical activity log for 1 wk. Measures for moderate, vigorous, recommended (i.e., met the criteria for moderate or vigorous), and strengthening activities were created according to Healthy People 2010 operational definitions. Reliability and validity were assessed using Cohen's kappa (kappa) and Pearson correlation coefficients.
Seventy-three percent of participants met the recommended activity criteria compared with 45% in the total U.S. population. Test-retest reliability (kappa) was 0.35-0.53 for moderate activity, 0.80-0.86 for vigorous activity, 0.67-0.84 for recommended activity, and 0.85-0.92 for strengthening. Validity (kappa) of the survey (using the accelerometer as the standard) was 0.17-0.22 for recommended activity. Validity (kappa) of the survey (using the physical activity log as the standard) was 0.40-0.52 for recommended activity.
The validity and reliability of the BRFSS physical activity questions suggests that this instrument can classify groups of adults into the levels of recommended and vigorous activity as defined by Healthy People 2010. Repeated administration of these questions over time will help to identify trends in physical activity.
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