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PubMed1999

Problematic formulations of SAS PROC.MIXED models for repeated measurements.

The work reported in this article was undertaken to evaluate the utility of SAS PROC.MIXED for testing hypotheses concerning GROUP and TIME x GROUP effects in repeated measurements designs with drop-outs. If dropouts are not completely at random, covariate control over informative individual differences on which dropout data patterns depend is widely recognized to be important. However, the inclusion of baseline scores and time-in-study as between-subject covariates in an otherwise well formulated SAS PROC.MIXED model resulted in inadequate control over type I error in simulated data with or without drop-outs present. The inadequate model formulations and resulting deviant test sizes are presented here as a warning for others who might be guided by the same information sources to employ similar model specifications when analyzing data from actual clinical trials. It is important that the complete model specification be provided in detail when reporting applications of the general linear mixed-model procedure. A single random-coefficients model produced appropriate test sizes, but it provided inferior power when informative covariates were added in the attempt to adjust for dropouts. As an alternative, the incorporation of covariate controls in simpler two-stage endpoint or random regression analyses is documented to be effective in dealing with dropouts under specifiable conditions.

Biopharmaceutics↗
PubMed1996

Effects of motion on the performance of pulse oximeters in volunteers.

BACKGROUND: Pulse oximetry is considered a standard of care in both the operating room and the postanesthetic care unit, and it is widely used in all critical care settings. Pulse oximeters may fail to provide valid pulse oximetry data in various situations that produce low signal-to-noise ratio. Motion artifact is a common cause of oximeter failure and loss of accuracy. This study compares the accuracy and data dropout rates of three current pulse oximeters during standardized motion in healthy volunteers. METHODS: Ten healthy volunteers were monitored by three different pulse oximeters: Nellcor N-200, Nellcor N-3000, and Masimo SET (prototype). Sensors were placed on digits 2, 3, and 4 of the test hand, which was strapped to a mechanical motion table. The opposite hand was used as a stationary control and was monitored with the same pulse oximeters and an arterial cannula. Arterial oxygen saturation rate varied from 100% to 75% by changing the inspired oxygen concentration. While pulse oximetry was both constant and changing, the oximeter sensors were connected before and during motion. Oximeter errors and dropout rates were digitally recorded continuously during each experiment. RESULTS: If the oximeter was functioning before motion began, the following are the percentages of time when the instrument displayed a pulse oximetry value within 7% of control: N-200 = 76%, N-3000 = 87%, and Masimo = 99%. When the oximeter sensor was connected after the beginning of motion, the values were N-200 = 68%, N-3000 = 47%, and Masimo = 97%. If the alarm threshold was chosen as pulse oximetry less than 90%, then the positive predictive values (true alarms/ total alarms) are N-200 = 73%, N-3000 = 81%, and Masimo = 100%. In general, N-200 had the greatest pulse oximetry errors and N-3000 had the highest dropout rates. CONCLUSIONS: The mechanical motions used in this study significantly affected oximeter function, particularly when the sensors were connected during motion, which requires signal acquisition during motion. The error and dropout rate performance of the Masimo was superior to that of the other two instruments during all test conditions. Masimo uses a new paradigm for oximeter signal processing, which appears to represent a significant advance in low signal-to-noise performance.

Adult↗
PubMed1997

The effects of motion on the performance of pulse oximeters in volunteers (revised publication).

BACKGROUND: Pulse oximetry is considered a standard of care in both the operating room and the postanesthetic care unit, and it is widely used in all critical care settings. Pulse oximeters may fail to provide valid SpO2 data in various situations that produce low signal-to-noise ratio. Motion artifact is a common cause of oximeter failure and loss of accuracy. This study compares the accuracy and data dropout rates of three current pulse oximeters during standardized motion in healthy volunteers. METHODS: Ten healthy volunteers were monitored by three different pulse oximeters: Nellcor N-200, Nellcor N-3000, and Masimo SET (prototype). Sensors were placed on digits 2, 3, and 4 of the test hand, which was strapped to a mechanical motion table. The opposite hand was used as a stationary control and was monitored with the same pulse oximeters and an arterial cannula. Arterial oxygen saturation was varied from 100% to 75% by changing the inspired oxygen concentration. While SpO2 was both constant and changing, the oximeter sensors were connected before and during motion. Oximeter errors and dropout rates were digitally recorded continuously during each experiment. RESULTS: If the oximeter was functioning before motion began, the following are the percentages of time when the instrument displayed an SpO2 value within 7% of control: N-200 = 76%, N-3000 = 87%, and Masimo = 99%. When the oximeter sensor was connected after the beginning of motion, the values were N-200 = 68%, N-3000 = 47%, and Masimo = 97%. If the alarm threshold was chosen SpO2 less than 90%, then the positive predictive values (true alarms/total alarms) are N-200 = 73%, N-3000 = 81%, and Masimo = 100%. In general, N-200 had the greatest SpO2 errors and N-3000 had the highest dropout rates. CONCLUSIONS: The mechanical motions used in this study significantly affected oximeter function, particularly when the sensors were connected during motion, which requires signal acquisition during motion. The error and dropout rate performance of the Masimo was superior to that of the other two instruments during all test conditions. Masimo uses a new paradigm for oximeter signal processing, which appears to represent a significant advance in low signal-to-noise performance.

Adult↗
PubMed1991

Changes in antisocial aggressiveness during treatment in a hierarchical therapeutic community. A prospective study of personality changes.

Thirty-six consecutive substance abusers were examined at intake and after 1 year of residency in a hierarchical therapeutic community using the personality instruments Million Clinical Multiaxial Inventory (MCMI) and Basic Character Inventory. Two antisocial aggressiveness subgroups were identified: a no-increase group (n = 11) that had high intake scores on MCMI antisocial aggression, small changes during the stay and a high dropout rate (45%) as outpatients; and an increase group (n = 25) with lower scores at intake and a low dropout rate (20%). A high level of antisocial aggressiveness at intake was related to dropout in the no-increase group, and a high degree of increase in antisocial aggressiveness was related to dropout in the increase group. The results show the importance of monitoring antisocial aggressiveness during treatment.

Adult↗
PubMed1985

Double-blind comparative study of paroxetine and amitriptyline in depressed patients of a university psychiatric outpatient clinic (pilot study).

21 depressed patients of the Basle University Psychiatric Outpatient Clinic were treated in a double-blind study with paroxetine and amitriptyline. 11 of these patients did not continue the trial until the end of the 7th week. There was a significant difference in the number of dropouts between the two groups: 80% of the amitriptyline group did not continue until the end, while in the paroxetine group we found only 30% dropouts. The patients of both groups showed a gradual decrease of the median total scores on the Hamilton and the Montgomery and Asberg Depression Rating Scales. Although the number of patients who stayed in the trial for at least 4 weeks (8 with paroxetine, 6 with amitriptyline) is quite small, we see from the results of the clinical global impression that the members of the paroxetine group improved most of all in the somatic symptoms, while considering their moods we found no differences between the groups. Patients of both groups complained about side effects, most of all about dry mouth and tiredness. From the high rate of dropouts under amitriptyline we found that the side effects under this drug were more severe and therefore led to the dropouts.

Adolescent↗
PubMedDate not supplied

Metaanalysis of randomized trials of the efficacy and safety of donepezil, galantamine, and rivastigmine for the treatment of Alzheimer disease.

The authors estimated the effects of each of the three commonly used drugs for Alzheimer disease (donepezil, galantamine, and rivastigmine) in terms of predefined clinical outcomes and trial completion rates, by dosing level, and described differences among them. Using both electronic and manual search strategies (January 1992 to July 2002), a metaanalysis examined the effect of the drugs on clinical outcomes and completion rates. Regression analyses compared the effect of dose on clinical outcomes and completion rates, using 10 donepezil, 6 galantamine, and 5 rivastigmine articles. All three drugs showed beneficial effects on cognitive tests, as compared with placebo. For donepezil and rivastigmine, larger doses were associated with larger effect. This was not the case with galantamine. The odds of clinical global improvement demonstrated superiority over placebo for each drug, with no dose effects noted. Dropout rates were greater with galantamine and rivastigmine. There was little difference in dropout rate for each drug at each dose-level, except with high-dose donepezil. This was accounted for by the high dropout rate in two 52-week studies using larger doses. In summary, all three drugs had similar cognitive efficacy, with donepezil and rivastigmine showing a dose effect across the dosing levels studied. However, both galantamine and rivastigmine were associated with a greater risk of trial dropout than placebo, especially at higher dosing levels.

Alzheimer Disease↗
PubMed2002

Problems in dealing with missing data and informative censoring in clinical trials.

Acommon problem in clinical trials is the missing data that occurs when patients do not complete the study and drop out without further measurements. Missing data cause the usual statistical analysis of complete or all available data to be subject to bias. There are no universally applicable methods for handling missing data. We recommend the following: (1) Report reasons for dropouts and proportions for each treatment group; (2) Conduct sensitivity analyses to encompass different scenarios of assumptions and discuss consistency or discrepancy among them; (3) Pay attention to minimize the chance of dropouts at the design stage and during trial monitoring; (4) Collect post-dropout data on the primary endpoints, if at all possible; and (5) Consider the dropout event itself an important endpoint in studies with many.

Journal Article↗
PubMed2001

Activity involvement among suicidal and nonsuicidal high-risk and typical adolescents.

The purpose of this study was to compare weekly activities among four groups of randomly selected high-risk and typical high school students: (1) potential dropouts at suicide risk, (2) typical youth at suicide risk, (3) potential dropouts not at suicide risk, and (4) typical youth not at suicide risk. Of the 1,286 participants, 39.4% of the high-risk and 30.1% of typical high school students screened in at suicide risk. Weekly activity comparisons across the four groups showed that suicide-risk adolescents, regardless of potential dropout status, engaged in more solitary activities on weekdays and weekends than did their nonsuicide risk peers. High-risk potential dropout youth engaged in less homework and more social activities during weekdays and weekends than did the typical high school students. These results provide important insight into the weekly activity involvement of at-risk youth while helping to gain a better understanding of suicide-risk adolescents. Implications of these findings are discussed for identifying youth at risk for suicidal behavior and for prevention programming.

Adolescent↗
PubMed1998

Effects of computer feedback on adherence to exercise.

A large fitness center setting was used to test the effects of a computer feedback system (FitLinxx Interactive Fitness Network) on adherence to exercise, attendance, and dropout. Healthy mixed-sex adult participants were evaluated on their maintenance of newly prescribed exercise. The control group (n = 71) used standard exercise tracking and feedback during exercise sessions. The treatment group (n = 93) used a specifically designed computer-based system that provided enhanced tracking, goal setting, and feedback. Analysis indicated significantly higher attendance and adherence in the treatment group who also had fewer dropouts by month, a larger number of days before dropout, and less over-all dropout (46%) over the 8 months tested. Discussion concerning the application of computerized feedback systems for maximizing clients' adherence within physical and cardiac rehabilitation and general fitness settings was given. Additional direct testing with different sample types and motivation was suggested.

Adult↗
PubMed2000

The Effect of Brochures and Audiotape on Efficacy and Tolerability of Venlafaxine in Depressed Outpatients: A Single-Blind Parallel Study in General Practice.

OBJECTIVE: The possible positive effects of brochures and an audiotape containing information on efficacy and tolerance on side effects, dropout rate, and clinical outcome of treatment with venlafaxine were studied in 1048 depressed outpatients (as clinically judged by the general practitioner; 740 women and 308 men), aged 18 to 85 years. METHOD: The study was of a single-blind, parallel-group design. All 4 groups were verbally informed: one group received only verbal information, a second group additionally received brochures, a third group additionally received information on audiotape, and a fourth group additionally received brochures and information on audiotape. There were 5 study visits, the first at baseline (week 0), followed by a visit at weeks 1, 2, 4, and 6. At each study visit, the Clinical Global Impressions scale, Zung Depression Scale, Quality of Life Scale, and State-Trait Anxiety Inventory were completed. The Patient's and Investigator's Subjective Ratings of Tolerance and Efficacy were completed at the final study visit. RESULTS: The brochures and audiotape reduced the dropout rate due to lack of efficacy (p =.01 and p =.04, respectively). In addition, the percentage of patients reporting side effects was lower in the group that received brochures than in the group that received only verbal information (p =.05). Additional information had no effect on efficacy measures. CONCLUSION: Supplying patients with education in the form of brochures and/or audiotape containing information on efficacy and tolerance of the drug reduces the dropout rate due to lack of efficacy. For the reduction of side effects, brochures in particular seem suitable. Information on audiotape or written information seems to lengthen the period that patients wait for the possible beneficial action of the medication. To reduce the dropout rate, it may be recommended that patients receive, in addition to brochures, spoken information on audiotape or compact disc.

Journal Article↗
PubMed2005

[Antiretroviral pharmaceutical expenditure and possibilities for optimization].

INTRODUCTION: A lack of treatment compliance, resistances and non-advanced stages of the disease are the reasons why not all HIV-infected patients benefit from the demonstrated efficacy of antiretroviral drug combinations--with the consequent important increase in costs. A prospective cohort follow-up study is conducted to analyze the distribution of antiretroviral pharmaceutical expenditure in a district hospital, and the possibilities for improving its efficiency. MATERIAL AND METHODS: The study comprised 128 HIV-infected patients seen for 12 consecutive weeks (September to November, 2004). The characteristics of previous follow-up were analyzed, and the patients were divided into groups according to the course over the following weeks and the results of prescribed treatment: group 1 (effective treatment), group 2 (ineffective treatment), and group 3 (treatment dropout). Based on the prescription history, corroborated with drug retrieval and the acquisition costs (FARMASYS software), the cost of antiretroviral medication was calculated for each of the 108 patients receiving highly active antiretroviral therapy (HAART). The statistical analysis was carried out with the SPSS version 11.5 statistical package, and considering statistical significance for p < 0.05. RESULTS: The cost generated by the 108 patients included during the study period who received HAART was 232,366 euros, with an average of 2,151 euros per patient and 19,363 euros per day of consultation. The distribution of patients and of the costs generated by the above defined groups was as follows: group 1: 79 patients (80.6%); group 2: 11 patients (10.6%); group 3: 18 patients (8.8%). In the group 1 patients, 15.2% of the antiretroviral expenditure corresponded to patients who had started therapy with a CD4+ count of > 350 cells/ml, while 45% had > 350 cells/ml at the present time, and 25.9% had > 500 cells/ml. Previous medication dropout was identified as a predictor of new dropouts and treatment failures. COMMENT: While the cost generated by antiretroviral medication is high, 19.4% is administered to patients who do not benefit from such treatment due to a lack of efficacy or dropouts, and in another 40-60% of cases the need for such treatment could be subject to consideration in view of the good immune status of the patients.

Adult↗
PubMed1999

Comparison of the efficacy and acceptability of atypical antipsychotic drugs: a meta-analysis of randomized, placebo-controlled trials.

Knowing the clinical differences of olanzapine, quetiapine, and risperidone would be of benefit for choosing an atypical antipsychotic drug. In order to compare their efficacy and acceptability, we conducted a meta-analysis of published, randomized, placebo-controlled trials by comparing the response and dropout rates of an atypical antipsychotic drug group and those of a placebo group. After a comprehensive search of study reports, the response and dropout rates of patients treated with an atypical antipsychotic drug and those treated with placebo were extracted on the intention-to-treat basis. The effect size with 95 per cent confidence interval (CI) of pooled data comparing the response and dropout rates of an atypical antipsychotic drug group and those of a placebo group were calculated by using the Peto method. The response-rate effect sizes (95% CIs) of olanzapine, quetiapine, and risperidone were 1.75 (1.06 to 2.89), 1.71 (1.20 to 2.42), and 3.28 (1.98 to 5.44), respectively. The dropout-rate effect sizes (95% CIs) of olanzapine, quetiapine, and risperidone were 0.55 (0.35 to 0.88), 0.65 (0.46 to 0.91), and 0.39 (0.24 to 0.62), respectively. In conclusion, olanzapine, quetiapine, and risperidone are more effective and more acceptable than placebo in treating schizophrenic patients. However, they are not different from each other in the respect of efficacy and acceptability. The cost of these agents should play an important role in choosing an atypical antipsychotic drug.

Antipsychotic Agents↗
PubMed2000

Tricyclic antidepressants for depressive disorders in children and adolescents: a meta-analysis of randomized-controlled trials.

The tricyclic antidepressants (TCAs) are effective for the treatment of adult depression. However, their efficacy of these in the treatment of children and adolescents with depression is equivocal. Therefore, it is necessary to determine the efficacy and acceptability of TCAs in the treatment of depressive disorders in children and adolescents. The databases of MEDLINE (from 1966 to October 1999) and Controlled Clinical Trials Registered (from 1980 to October 1999) were searched for randomized-controlled trials relevant to the use of TCAs for treating depressed children and adolescents. The reviewers also examined the reference lists of identified papers and that of a previous meta-analysis. In each trial, both nonresponse rates and dropout rates were taken into account and extracted on an intention-to-treat basis. The nonresponse-rate and dropout-rate odd ratios (ORs) with 95 per cent confidence intervals (95% CIs) of each trial and the pooled non-response-rate and dropout-rate ORs (95% CIs) of all trials were computed. Nine trials included in this meta-analysis were 2 amitriptyline, 3 desipramine, 2 imipramine, and 2 nortriptyline studies. By using a fixed-effect model, the pooled nonresponse-rate OR (95% CI) and the pooled dropout rate OR (95% CI) of antidepressant-treated group were 0.92 (0.57 to 1.47) and 2.14 (1.12 to 4.09), respectively. In summary, the evidence so far does not support that TCAs are more effective or more acceptable than placebo in the treatment of depressive disorders in children and adolescents. However, the studies of selective serotonin reuptake inhibitors and newer antidepressants for the treatment of these disorders should be further investigated.

Adolescent↗
PubMed1996

High flux peritoneal membrane is a risk factor in survival of CAPD treatment.

A high dropout rate is a major problem of continuous ambulatory peritoneal dialysis (CAPD) treatment. Serum albumin is both a significant parameter of dropout in CAPD and a predictor of peritoneal transport category based on the peritoneal equilibration test (PET). High flux peritoneal membrane (HFPM) may lose more protein in the dialysate. We examined the effect of HFPM on the survival of treatment of CAPD. The study was composed of 171 adult patients who had standard PET. The peritoneal transport category was based on their first PET after starting CAPD. The HFPM was defined as the dialysate-to-plasma creatinine concentration ratio (D/P) of more than one standard deviation of the mean (0.702 +/- 0.114; D/P > 0.816). Twenty-two patients had HFPM. The other 149 patients were categorized as the non-high flux group. The high flux group had a significantly lower serum albumin at PET (3.07 +/- 0.15 vs 3.68 +/- 0.05 g/dL, respectively p < 0.0001) and lower mean serum albumin during treatment than the non-high flux group (3.40 +/- 0.20 vs 3.70 +/- 0.04 g/dL, respectively, p = 0.020), and lower net drainage volume (p = 0.0007), but age, diabetes, total Kt/V, and total normalized weekly creatinine clearance were not different between groups. The risk of dropout was higher in the high flux group (p = 0.0127, Cox-Mantel log rank test), and the risk increased, especially after 1.5 years of treatment. Corrected for other risk factors, patients who had HFPM have two times the risk of dropout compared to the non-high flux groups (p = 0.0401, Cox proportional hazards model).

Adolescent↗
PubMed1981

A randomized prospective study of the use-effectiveness of two methods of natural family planning.

The final results of a prospective comparative study of two methods of natural family planning indicate a significant difference in the 12 month net cumulative pregnancy rates between the ovulation and symptothermal methods. These differences are on the order of two to one in favor of the symptothermal method. Pearl pregnancy rates confirm similar differentials between the two methods. Dropout rates for both methods were high. Lack of interest or dissatisfaction with the method was the major reason for dropout training while pregnancy or desire for pregnancy were the major reasons for dropout during the formal phase of the study.

Adult↗
PubMed2004

Auditory brainstem implantation in 12- to 18-year-olds.

OBJECTIVE: To assess the effects of the side of implantation (first-side vs second-side vestibular schwannoma); the presence of nonauditory sensations; the general health, expectations, and motivation of the patients; and a support group on the use of a multichannel auditory brainstem implant (ABI) in 12- to 18-year-old patients with neurofibromatosis 2. DESIGN: Since 1992, 21 individuals (age range, 12-18 years) who were deafened by neurofibromatosis 2 have undergone implantation with a multichannel ABI at the House Ear Institute, Los Angeles, Calif. The patients were categorized regarding side of implantation, presence of remaining hearing (in first-side implant recipients), incidence of nonauditory sensations, and ABI use or nonuse. They were also rated on factors of general health, personal motivation, expectations, and family support. RESULTS: Nineteen (95%) of 20 teenagers tested received hearing sensations from their ABIs. Eleven teenagers used their ABIs regularly, but 8 did not. Of the nonusers, 2 had good remaining hearing on the side with the second vestibular schwannoma, 2 had persistent nonauditory sensations, and 4 became program dropouts. None of the dropouts had remaining hearing, significant nonauditory sensations, or poor health; however, they generally rated poorly in terms of personal motivation, expectations, and family support. One patient with good family support returned with excellent ABI results after 4 years' absence. CONCLUSIONS: The multichannel ABI is an effective means of providing hearing sensations to young patients deafened by neurofibromatosis 2. Preoperative counseling regarding the importance of such factors as expectations, personal motivation, and family support is invaluable and can promote successful adaptation to the device. With patience and support, even young nonusers (including program dropouts) can become successful device users.

Adolescent↗
PubMed2000

The relationship between marijuana initiation and dropping out of high school.

The prevalence of marijuana use among young people has risen rapidly in recent years, causing concern over the potential impact on academic performance of such use. While recent studies have examined the effect of alcohol use on educational attainment, they have largely ignored the potential negative effects of other substances, such as marijuana. This paper examines whether the relationship between the initiation of marijuana use and the decision to drop out of high school varies with the age of dropout or with multiple substance use. Data are from a longitudinal survey of 1392 adolescents aged 16-18 years. The results suggest that marijuana initiation is positively related to dropping out of high school. Although the magnitude and significance of this relationship varies with age of dropout and with other substances used, it is concluded that the effect of marijuana initiation on the probability of subsequent high school dropout is relatively stable, with marijuana users' odds of dropping out being about 2.3 times that of non-users. Implications of these conclusions are considered for both policy makers and researchers.

Adolescent↗
PubMed2005

Percutaneous radiofrequency ablation of hepatocellular carcinoma as a bridge to liver transplantation.

Orthotopic liver transplantation (OLT) can be a definitive treatment for patients with hepatocellular carcinoma (HCC). Prolonged waiting times for cadaveric livers, however, may lead to dropout from the waiting list or worsened post-OLT prognosis as a result of interval tumor progression. Percutaneous radiofrequency ablation (RFA) is widely used for local control of small unresectable HCC, but its pretransplant role remains unclear. We studied the outcome of 52 consecutive patients accepted for OLT bearing 87 HCC nodules and treated with percutaneous RFA. On initial staging, the tumor burden exceeded the Milan criteria in 10 patients. Complete tumor coagulation was observed in 74 of 87 (85.1%) nodules based on postablation imaging. After a mean of 12.7 months (range: 0.3-43.5) on the waiting list, 3 of 52 patients (5.8%) had dropped out due to tumor progression. Forty-one patients had undergone transplantation, with 1- and 3-year post-OLT survival rates of 85% and 76%, respectively. No patient developed HCC recurrence. There were three major complications in 76 RFA procedures (hepatic arterial hemorrhage, small bowel perforation, and liver decompensation salvaged by OLT), without resultant death or dropout. In conclusion, percutaneous RFA is an effective bridge to OLT for patients with compensated liver function and safely accessible tumors. Tumor-related dropout rate and post-OLT outcome compared favorably with published controls of patients with early-stage disease. This can be attributed to the efficacy of RFA in producing local cure or curbing tumor progression during the waiting period.

Adult↗