Difference In Mean Rate Research Articles

Testing the Significance of Difference in Average Rates of Change in Controlled Longitudinal Studies With High Dropout Rates

This article concerns methodology for testing the significance of differences in mean rates of change in controlled repeated measurements designs with limited sample sizes, autoregressive error structures, nonlinear patterns of underlying true mean change, dropout rates exceeding 50%, plus other missing data. Each of these is problematic for ordinary repeated measures analysis of variance, and a complex generalized linear mixed model formulation popularly advocated for the ability to deal with autoregressive error structures and missing data is shown to perform poorly in such circumstances. Monte Carlo simulation methods confirm that simple two-stage analyses of dropout-weighted linear slope coefficients provide conservative Type 1 error protection, although adequate power requires the presence of large treatment effects in studies with the limited sample sizes and high proportions of missing data. No other analysis has been documented to provide both conservative Type 1 error protection and competitive power under similarly taxing conditions.

Are Comparisons of Consumer Satisfaction With Providers Biased by Nonresponse or Case-Mix Differences?

Are Comparisons of Consumer Satisfaction With Providers Biased by Nonresponse or Case-Mix Differences?

Standard Of Measurement For Student Evaluation Instruments

For colleges and universities, the expectation for excellence in teaching and learning has made development of a system for measuring teaching effectiveness critical. Teaching effectiveness is generally assessed with a comprehensive review of skills including instructional design, instructional delivery and course management. This requires student feedback usually in the form of Student Evaluation Instruments (SEIs). Since SEIs are an important part of measuring teaching effectiveness to assess excellence, and excellence in the classroom is expected when considering promotion and tenure, it follows that they play an integral role in the promotion and tenure process. In fact, faculty promotions and the issuance of tenure may hinge on the results of these vital evaluations. Our study investigates the use of SEIs at our university’s School of Business. Unlike many other prior studies, limited to a single course or department and a single semester, we examined data collected from the use during six semesters (three years) of our Student Evaluation Instrument for the entire School of Business. The results yielded nearly 30,000 useable responses across all business majors. If SEIs are to be used effectively and fairly then one must have a clear understanding as to what should be the appropriate standard used to evaluate faculty teaching effectiveness. Should a global value – the mean for the entire school or university – be used or should it be based on the mean for each department? We believe this to be a critical consideration given the potential for differences in mean ratings amongst departments.

Indices of Choking under Pressure among Athletes during Competition

This study provides information on choking under pressure among university athletes during competition. 300 athletes were sampled and rated on a questionnaire on external and internal perceived sources of choking (alpha = .69 and .72). Analysis indicates a significant difference in mean rating on the two choking indices for men and women athletes. The women's means were higher than the men's but the difference was less than 1.00. Means for four sport groups were similar for the Internal subscale but significantly different on the External subscale.

More Time to Taste. Focus on “Variability in Responses and Temporal Coding of Tastants of Similar Quality in the Nucleus of the Solitary Tract of the Rat”

The taste system is ideal for investigations of temporal coding, because neural taste responses are time extensive and often difficult to differentiate by magnitude alone. In a recent article, [Roussin et al. 2008][1] show that spike-time patterning provides a necessary and efficient source of

Analysis of Data from a Controlled Repeated Measurements Design with Baseline-Dependent Dropouts

Abstract. Differences in mean rates of change are of primary interest in many controlled treatment evaluation studies. Generalized linear mixed model (GLMM) procedures are widely conceived to be the preferred method of analysis for repeated measurement designs when there are missing data due to dropouts, but systematic dependence of the dropout probabilities on antecedent or concurrent factors poses a problem for testing the significance of differences in mean rates of change across time in such designs. Controlling for the dependence of dropout probabilities on baseline values poses a special problem because a theoretically correct GLMM random-effects model does not permit including the same baseline score as both covariate and dependent variable. Monte Carlo methods are used herein to evaluate the actual Type 1 error rates and power resulting from two commonly-illustrated GLMM random-effects model formulations for testing the GROUPS × TIMES linear interaction effect in group-randomized repeated measurements designs. The two GLMM model formulations differ by either including or not including baseline scores as a covariate in the attempt to control for imbalance caused by the baseline-dependent dropouts. Results from those analyses are compared with results from a simpler two-stage analysis in which dropout-weighted slope coefficients fitted separately to the available repeated measurements for each subject serve as the dependent variable for an ordinary ANCOVA test for difference in mean rates of change. The Monte Carlo results confirm modestly superior Type 1 error protection but quite superior power for the simpler two-stage analysis of dropout-weighted slope coefficients as compared with those for either of the more mathematically complex GLMM analyses.

Assessments by Patients With Schizophrenia and Psychiatrists of Relative Risk of Research Procedures

Assessments by Patients With Schizophrenia and Psychiatrists of Relative Risk of Research Procedures

Evaluation of bath grab bar placement for older adults

The patterns of use, perceived usefulness and perceived safety of five different configurations of bathtub grab bars were evaluated by 103 community-living seniors in Canada. Current bathing activities, fall history, sociodemographic characteristics, balance measures as well as details about the home bathing environment were recorded. Participants were then videotaped as they got into, sat down, got up and exited a bath tub using each of the five configurations. The videotapes were used to determine the pattern of grab bar use for each and participants ranked each for perceived function and safety. The five configurations corresponded to standards published by the Canadian Standards Association, the US Uniform Accessibility Standards, a modification of the Ontario Building code (OBC, a Canadian provincial code), a common configuration and a composite configuration. Although most respondents did not have bathtub grab bars installed in their home, those with home bars reported that they used the bars on a regular basis. Significant differences in mean ratings of safety, comfort, ease of use, helpfulness, likelihood of use, and total composite score were detected between configurations with the modified OBC consistently ranked least favourable. There were no statistically significant relationships between the respondents' profiles, their preferred configurations or their patterns of bar use. A series of recommendations and suggestions for future research are made.

Rule‐of‐thumb adjustment of sample sizes to accommodate dropouts in a two‐stage analysis of repeated measurements

Recent contributions to the statistical literature have provided elegant model-based solutions to the problem of estimating sample sizes for testing the significance of differences in mean rates of change across repeated measures in controlled longitudinal studies with differentially correlated error and missing data due to dropouts. However, the mathematical complexity and model specificity of these solutions make them generally inaccessible to most applied researchers who actually design and undertake treatment evaluation research in psychiatry. In contrast, this article relies on a simple two-stage analysis in which dropout-weighted slope coefficients fitted to the available repeated measurements for each subject separately serve as the dependent variable for a familiar ANCOVA test of significance for differences in mean rates of change. This article is about how a sample of size that is estimated or calculated to provide desired power for testing that hypothesis without considering dropouts can be adjusted appropriately to take dropouts into account. Empirical results support the conclusion that, whatever reasonable level of power would be provided by a given sample size in the absence of dropouts, essentially the same power can be realized in the presence of dropouts simply by adding to the original dropout-free sample size the number of subjects who would be expected to drop from a sample of that original size under conditions of the proposed study.

A two‐stage analysis of repeated measurements with dropouts and/or intermittent missing data

This article is about a simple two-stage analysis that utilizes slope coefficients as the dependent variable for testing the significance of difference in mean rates of change in repeated measurement designs with missing data. The ANCOVA test on the doubly weighted slope coefficients provides power comparable to that of more complex maximum likelihood procedures when data are missing completely at random, requires fewer assumptions and is more generally applicable under realistic nonrandom dropout conditions, and most importantly can be readily understood and explained by those who actually do most controlled clinical research.

Effect of hyperbaric oxygenation on intracranial pressure elevation rate in rats during the early phase of severe traumatic brain injury

Intracranial pressure (ICP) was monitored to evaluate the therapeutic effect of hyperbaric oxygen (HBO 2) treatment following traumatic brain injury (TBI). This subject is controversial. The aim of our study was to determine whether HBO 2 treatment has a therapeutic effect on ICP dynamics and survival following severe fluid percussion brain injury (FPBI) in rats. Changes in ICP level were analyzed every 30 min during an 8-h monitoring period following trauma and at the end of experiment (20 h). The control (A) and experimental (B) groups consisted of 7 and 4 rats, respectively. Group B was subjected to 1.5 atmospheres absolute (ATA) 100% oxygen for 60 min beginning 2 h after FPBI. No significant differences in ICP were noted between groups A and B before and after HBO 2 treatment until 3.5 h after trauma. At 4 h, for the first time, the difference became significant ( P = 0.025; n = 11) and remained significant ( P < 0.05) for all measurement points until end of monitoring, when mean ICP values reached 37.17 ± 14.25 and 20.25 ± 2.63 mm Hg in groups A and B, respectively. Linear approximation models showed different trends (b1 = 3.80 ± 0.23; r 2 = 0.65, P < 0.001 and b1 = 1.56 ± 0.25; r 2 = 0.77, P < 0.001) for groups A and B, respectively. Covariance analysis confirmed significant differences between slopes for groups A and B ( F = 148.04, P < 0.001; df = 2,177), i.e., a significant difference in mean rate of ICP elevation. By the end of the experiment, 3 out of 7 rats from group A had died, but none from group B. We conclude that the application of HBO 2 during the early phase of severe FPBI significantly diminished ICP elevation rate and decreased mortality level.

Propofol versus Midazolam/Fentanyl for Reduction of Anterior Shoulder Dislocation

The authors aimed to compare propofol and midazolam/fentanyl for reduction of anterior shoulder dislocations using the modified Kocher's maneuver. This was a multicenter, randomized, clinical trial of patients with anterior shoulder dislocation. Patients were randomized to either propofol or midazolam/fentanyl. The randomized drug was titrated to a clinical sedation end point (spontaneous eye closure). One physician sedated the patient. Another, blinded to the drug administered, reduced the shoulder and recorded details of muscle tone and ease of reduction. Eighty-six patients were randomized to treatment with propofol (n = 48) or midazolam/fentanyl (n = 38). Patients in the propofol group had shorter mean times to first wakening (difference in means, 4.6 minutes; 95% confidence interval [CI] = 0.7 to 8.6; p = 0.097) and full consciousness (difference in means, 21.7 minutes; 95% CI = 14.7 to 28.7; p <0.001), had easier shoulder reduction (difference in mean rating, 0.5; 95% CI = 0.0 to 0.9; p = 0.047), and needed fewer reduction attempts (difference in means, 0.5; 95% CI = 0.1 to 1.0; p = 0.02). Patients in the propofol group also had less mean muscle tone at the first reduction attempt (p = 0.08) and needed fewer reduction maneuvers (p = 0.40) but had more respiratory depression (11 vs. six patients; difference in proportions, 7.1%; 95% CI = -11.8 to 26.1; p = 0.58) and had one patient who vomited. Propofol appears to be as effective as midazolam/fentanyl for reduction of anterior shoulder dislocation using the modified Kocher's maneuver. However, the advantage of shorter wakening times associated with propofol should be weighed against the possibility of adverse events, particularly respiratory depression and vomiting.

Ratings of Perceived Exertion are Not Influenced by Exercise Stage of Change in Physically Active College Students

Comparisons of ratings of perceived exertion based on fitness have been equivocal but have not accounted for recent exercise history. The purpose of this study was to test mean differences in ratings of perceived exertion among individuals of differing exercise histories as measured by exercise stage of change. Participants completed questionnaires to measure exercise stage of change and physical activity [preparation stage (n=32), action stage (n=31), and maintenance stage (n=41)]. Ratings of perceived exertion were measured during a graded maximal exercise test. Individual regression equations were computed to estimate the ratings for 50%, 60%, 70%, and 80% of VO2 max. There were no significant differences in the ratings across the preparation, action, and maintenance stages. Therefore, the hypothesis that recent exercise history would influence ratings of perceived exertion during an aerobic fitness test was rejected.

Unscheduled care for people with asthma in a multi-ethnic area is reduced following educational outreach programme by specialist nurses

Question Do asthma specialist nurses reduce health service use and improve outcomes across different ethnic groups? Study design Cluster randomised controlled trial. Main results Specialist nurse intervention reduced the percentage of participants attending unscheduled care in the subsequent year compared with usual care (adjusted odds ratio with clustering 0.61, 95% CI 0.38 to 0.99). First attendance for unscheduled asthma care in the same time period was delayed by specialist nurse intervention (hazard ratio [HR] 0.73, 95% CI 0.54 to 1.00). The effect of specialist nurse intervention on time to attendance was greater in white people (HR 0.57, 95% CI 0.38 to 0.85) compared with South Asian people (HR 0.72, 95% CI 0.48 to 1.09) or other ethnicities (HR 1.29, 95% CI 0.51 to 3.22). There were no significant difference in mean rates of hospital admission between groups. Authors’ conclusions Unscheduled care for people with asthma was reduced in practices where asthma specialist nurses provided an educational outreach and clinical support programme to staff. Improved outcomes were not equally distributed among ethnic groups.

What do medicine clerkship preceptors do best?

Students' ratings of preceptors are widely used in medical education for feedback and evaluation purposes. The present study investigated students' ratings of the clinical teaching skills of inpatient attending physicians, inpatient residents, and outpatient attending physicians to assess differences among types of preceptors and relative strengths and weaknesses. A total of 268 students from three academic years (1997-2000) at one medical school rated preceptors on an end-of-clerkship evaluation, for a total of 1,680 ratings. When the ratings were aggregated by preceptors' names and types, there were 691 mean ratings of preceptors. Relative strengths and weaknesses were identified. Differences in mean ratings by preceptor type (inpatient attending physician, inpatient resident, and outpatient attending physician) were evaluated, and strengths and weaknesses were identified by rank ordering the items' means. Students tended to rate outpatient attending physicians higher than inpatient attending physicians or residents. Areas where ratings suggested relative strengths included showing an interest in teaching, respecting students' opinions, and being available to students. Areas of relative weakness included increasing physical examination and interviewing skills. Students' ratings are useful for identifying strengths and weakness for groups of preceptors and, as such, are important sources of information for setting priorities for faculty development efforts.

Rates of cesarean births in Hong Kong: 1987-1999.

High cesarean birth rates are an issue of international public health concern. The purpose of this paper was to examine the annual incidence and secular trend of cesarean births in Hong Kong and to correlate these rates with socioeconomic, demographic, and health indicators for the population since 1987. This was a descriptive and ecologic study. Annual population rates of cesarean sections were estimated for 1987 from a population-based survey, and for 1993 through 1999 from government data sources. The number of excess cesarean sections was calculated for each year using the 15 percent upper limit as proposed by the World Health Organization. From 1987 to 1999 the overall annual cesarean section rate rose steadily from 16.6 to 27.4 per 100 hospital deliveries, resulting in a 65 percent increase over 12 years. The mean difference in rates of surgical delivery between public (mean(public) = 16.0%) and private (mean(private) = 43.4%) institutions was 27.4 percent (95% confidence interval (CI) = 24.1, 30.7; p < 0.001). This is the first systematic report of secular variations of cesarean delivery rates in Asia. The high rates and increasing trend represent an unnecessary excess risk for mothers and their infants. Various strategies combating high cesarean rates have been proposed and have succeeded elsewhere. Concerted action from health care professionals, public health authorities, the general population, and the media is urgently required to implement solutions to reduce the rate of cesarean delivery.

Velocity Invariance of Receptive Field Structure in Somatosensory Cortical Area 3b of the Alert Monkey

This is the second in a series of studies of the neural representation of tactile spatial form in cortical area 3b of the alert monkey. We previously studied the spatial structure of 330 area 3b neuronal receptive fields (RFs) on the fingerpad with random dot patterns scanned at one velocity (40 mm/sec; ). Here, we analyze the temporal structure of 84 neuronal RFs by studying their spatial structure at three scanning velocities (20, 40, and 80 mm/sec). As in the previous study, most RFs contained a single, central, excitatory region and one or more surrounding or flanking inhibitory regions. The mean time delay between skin stimulation and its excitatory effect was 15.5 msec. Except for differences in mean rate, each neuron's response and the spatial structure of its RF were essentially unaffected by scanning velocity. This is the expected outcome when excitatory and inhibitory effects are brief and synchronous. However, that interpretation is consistent neither with the reported timing of excitation and inhibition in somatosensory cortex nor with the third study in this series, which investigates the effect of scanning direction and shows that one component of inhibition lags behind excitation. We reconcile these observations by showing that overlapping (in-field) inhibition delayed relative to excitation can produce RF spatial structure that is unaffected by changes in scanning velocity. Regardless of the mechanisms, the velocity invariance of area 3b RF structure is consistent with the velocity invariance of tactile spatial perception (e.g., roughness estimation and form recognition).

Additional Evidence of Attitudinal Influences in Performance Appraisal

The attitudes of twenty-nine managers toward performance appraisal and toward their organization were used to predict differences in mean ratings and measures of discrimination among ratees and performance dimensions. Substantial multiple correlations were obtained for all three dependent variables (between 32 and 46% of the variance in each measure was explained), and several individual correlations were statistically significant. Raters who showed low levels of confidence in the appraisal system, high levels of discomfort, or high levels of instrumental commitment were more likely to provide ratings that were unusually high or that did not discriminate well among ratees and/or dimensions. Raters who showed higher levels of attitudinal commitment or who perceived more risks associated with distorting ratings tended to provide lower ratings and to discriminate among ratees and/or dimensions.

Assessing Adherence to a Rotary Diversified Diet, a Treatment for ‘Environmental Illness’

Objectives To develop and test a method to assess adherence to a rotary diversified diet (RDD), a treatment for environmental illness, which is a putative disorder characterized by multiple sensitivities to foods, chemicals, or inhalants. The RDD requires the elimination of prohibited foods and rotation of remaining nonprohibited foods and their “food families” within a 4- to 7-day cycle. The regimen has yet to be validated to the satisfaction of the scientific community. Design Details of the 2 components of the RDD prescription, elimination and rotation, were documented, and a food record method of assessing adherence was developed. Adherence to the RDD was then assessed in a cohort of women who were enrolled in a larger prospective study. Test-retest reliability of the adherence assessment method was determined by calculating ratings twice on the same set of patient food records, with 1 week between trials. Subjects/setting All patients were contacted through a private environmental medicine clinic in Toronto, Canada. Eight patients provided the food records needed for development of the method; adherence was then assessed in 22 women aged 25 to 67 years. Statistical analyses Means, standard deviations, and 95% confidence intervals for adherence ratings were calculated. The reliability of the adherence assessment method was determined by calculating Pearson correlation coefficients for adherence ratings from each trial. A paired t test was also used to determine if the mean differences in ratings between trials were significant. Results Patients experienced difficulties following both components of the RDD: 37% to 44% of foods consumed were either prohibited or allowed, but were consumed on the incorrect day. The adherence assessment method was found to have high levels of reliability. Applications The adherence assessment method can be used in future evaluations of the RDD, although further testing of the method is recommended. Increased involvement of dietitians with patients diagnosed with environmental illness is recommended. J Am Diet Assoc. 1998;98:1439–1444.

Impression formation as a function of male baldness.

A computer-morphing procedure was used to produce a "full cranial hair" photograph for comparisons of perceptions by 96 undergraduates of a photograph of a naturally bald 30-yr.-old man on 13 dependent measures derived from 30 semantic differential scales. Analysis showed the full-hair condition was rated significantly more dominant, dynamic, and masculine than the bald condition. While the model was also perceived as younger in the full-hair condition, there was no difference in mean ratings of attractiveness between photographs.