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PubMed2001

Anthropometric and demographic factors affecting distance hopped and limb symmetry index for the crossover hop-for-distance test in high school athletes.

STUDY DESIGN: Prospective cohort study using a random selection from an accessible population. OBJECTIVES: We examined anthropometric and demographic characteristics affecting distance hopped (DH) and limb symmetry index (LSI) in the crossover hop-for-distance test in uninjured high school athletes. BACKGROUND: Between-subject comparisons of hop test results described by DH and LSI are common in the literature and clinical practice. The effect that anthropometric traits and demographic characteristics have on these measures is uncertain but must be known to correctly interpret hop-for-distance test results in research or to determine suitability of return to sports. METHODS AND MEASURES: For 201 high school athletes (age = 15.15+/-1.45 years, mean weight = 63.67+/-14.02 kg, mean height = 167.92+/-9.58 cm) completing the crossover hop-for-distance test, we recorded maximum DH for each leg and calculated the LSI of each subject. We performed 2 separate step-wise regression analysis models to develop predictive equations for DH and LSI. RESULTS: Age (r = 0.36), weight r = 0.41), and body fat percentage (r = 0.58) were significant predictors of DH, with the regression model explaining 59% of the variability. None of the measured variables were significant predictors of LSI (r = 0.03). The regression model explained only 3% of the variability of LSI. CONCLUSIONS: The LSI for the crossover hop-for-distance test can be compared among all individuals without subdividing into groups. Subject characteristics should be as homogeneous as possible when comparing DH among subjects or groups.

Adipose Tissue↗

PubMedDate not supplied

Three measures of sleep, sleepiness, and sleep deprivation and the risk of injury: a case-control and case-crossover study.

PURPOSE: Sleepiness and sleep deprivation are associated with injury, but few case-control studies have addressed them. We sought to add to the body of analytic observational studies. METHODS: Case-control and case-crossover study of 2517 injured patients interviewed in person in 3 emergency departments and matched by age, sex, rural versus urban, day of week, and hour of day with 1856 controls. Sleep constructs were measured by the following: (1) self-perceived sleepiness at injury or matched control time using 3 adjectives (tired, sleepy, drowsy); (2) usual sleep quality and quantity, and differences in those in the past 7 days; and (3) hours of sleep in the 24 hours before injury and the 24 hours before that. RESULTS: Better sleep quality in the past 7 days was associated with a lower risk of injury (odds ratio (OR) 0.88, 95% confidence interval (CI) 0.80 to 0.97). Self-reported sleepiness just before injury compared with control time was associated with a lower risk of injury, with ORs of 0.82 per unit on a 0-to-12 scale (95% CI 0.78 to 0.86) in case-control analysis and 0.76 (0.73 to 0.80) in case-crossover analysis. In case-crossover analysis, additional sleep in the 24 hours before injury compared with the 24 hours before that was associated with an increased risk of injury (OR 1.06 per hour, 95% CI 1.03 to 1.09), but this effect disappeared when we controlled for activity, location, and recent alcohol consumption. CONCLUSIONS: Better recent sleep quality was associated with a lower risk of injury, but surprisingly, feeling sleepy was also.

Adolescent↗

PubMed2005

A comparative crossover study of the effects of fluvastatin and pravastatin (FP-COS) on circulating autoantibodies to oxidized LDL in patients with hypercholesterolemia.

This study compared the effects of fluvastatin and pravastatin on the in vivo oxidation of LDL in a crossover design to evaluate whether or not it is justified to switch between the two statins with regard to serum levels of lipids, lipoproteins, and apolipoproteins (apo), and circulating autoantibodies to oxidized LDL (OxLDL-Ab). Patients with hypercholesterolemia (n = 46) were randomly assigned into groups who received fluvastatin (20 mg/d) or pravastatin (10 mg/d). After 3 months, they were crossed to receive the other statin for another 3 months. Circulating levels of OxLDL-Ab were measured by an OxLDL IgG ELISA test. Fluvastatin and pravastatin similarly decreased serum levels of total cholesterol (TC), LDL-C, and apo B, and increased HDL(2)-C levels. After crossover to the other statin, these lipid parameters were not further changed by either statin. Before crossover, circulating levels of OxLDL-Ab were decreased in patients with fluvastatin treatment, but not in those with pravastatin treatment. After switching from the other statin, both fluvastatin and pravastatin further decreased OxLDL-Ab levels. In conclusion, fluvastatin at 20 mg/d and pravastatin at 10 mg/d are similar with regard to their efficacy in decreasing TC, LDL-C, and apo B levels and increasing HDL(2)-C levels. Fluvastatin lowered circulating levels of OxLDL-Ab, and these effects continued after switching to pravastatin.

Autoantibodies↗

PubMed2002

Efficacy of combined, sequential and crossover psychotherapy and pharmacotherapy in improving outcomes in depression.

There is a growing recognition that relapse and recurrence after the successful treatment of major depression is a common and debilitating outcome that has massive social costs. Although many patients achieve a sustained recovery with maintenance pharmacotherapy, the long-term outcome for a significant proportion of patients is still poor. The purpose of this review is to evaluate the role of combined psychological and pharmacological therapies in minimizing relapse and recurrence in the treatment of depression. Three approaches have been investigated: concurrent treatment, sequential treatment and crossover treatment. Concurrent therapy is as effective as monotherapy for the treatment of mild-to-moderate depressive disorder and shows evidence of a potential treatment advantage in cases where depression is more severe. Consecutive sequencing of pharmacotherapy and psychotherapy has demonstrated some benefit for both the conversion of partial to full response and the prevention of relapse and recurrence, especially in more severely depressed patients. Crossover treatments during the maintenance phase (i.e., switching patients from one treatment to a second after an adequate response to the first) show evidence of being beneficial in preventing relapse and recurrence. Variants of cognitive therapy that have been modified to specifically address residual symptoms in patients who have recovered from depression appear to be the most effective. A review of the studies to date indicates that cognitive therapy may play a role in improving remission rates and decreasing relapse and recurrence rates. Although most studies are small, there is a consistent suggestion of superior prophylaxis for patients receiving some type of sequenced or crossover treatment in which the delivery of antidepressant medication and structured antidepressant psychotherapy is combined. These approaches warrant greater attention; they may present another route for enhancing long-term recovery from major depression.

Antidepressive Agents↗

PubMed2005

Patient preference in a crossover clinical trial of patients with osteoarthritis of the knee or hip: face validity of self-report questionnaire ratings.

OBJECTIVE: To analyze correlational validity of self-report responses regarding patient preference between 2 drugs at the conclusion of a crossover double-blind clinical trial in patients with osteoarthritis (OA) of the knee or hip. METHODS: Patients were randomized to 6 weeks' treatment of diclofenac/misoprostol or acetaminophen, followed by crossover to 6 weeks of the other drug. Patient preference was queried at the final visit: "Please compare control of your arthritis during the first and second periods as 'much better' or 'better' in the first period, 'no different' or 'better' or 'much better' in the second period." Patient preference ratings were evaluated in comparisons with 4 independent self-report measures within each treatment period: (1) change in Western Ontario McMaster (WOMAC) questionnaire scores; (2) change in pain visual analog scale (VAS) on a multidimensional Health Assessment Questionnaire (MDHAQ); (3) patient ratings of drug efficacy; and (4) patient report of change in arthritis status, as well as investigator ratings of the more efficacious drug. RESULTS: Among 173 patients, diclofenac/misoprostol was rated as "much better" by 54 and "better" by 45, acetaminophen was rated as "better" by 18 and "much better" by 17, and "no difference" by 39 patients. Spearman rank correlations for patient preferences were significant for changes in WOMAC scores, pain VAS, and independent patient ratings of drug efficacy and changes in arthritis status within each treatment period, as well as with physician ratings of the more efficacious drug (p < 0.001). CONCLUSION: Significant correlational validity is documented for patient self-report of preferences between 2 drugs compared to independent measures within each treatment period in this crossover clinical trial in patients with OA of the knee or hip.

Acetaminophen↗

PubMed2005

Comparative efficacy of a new battery-powered toothbrush and a commercially available manual toothbrush on the removal of established supragingival plaque: a single-use crossover study in adults.

OBJECTIVE: The objective of this single-use, examiner-blind, two-treatment crossover clinical study was to evaluate the efficacy of a new battery-powered toothbrush (Colgate MicroSonic) relative to that of a currently marketed manual toothbrush (Oral-B Indicator) for the removal of supragingival plaque. This study included the assessment of plaque removal in the whole mouth, at the gumline, and at interproximal sites via the comparison of pre- and post-brushing plaque levels measured using the Rustogi Modification of the Modified Navy Plaque Index. METHODOLOGY: Qualifying adult male and female subjects from the Newark, New Jersey area were provided with a commercially available toothbrush (Colgate Plus Toothbrush) and dentifrice (Colgate Cavity Protection Great Regular Flavor Fluoride Toothpaste) to use at home for three days before beginning the first phase of the crossover study. Subjects returned to the study site after refraining from any oral hygiene procedures for twenty-four hours, and from eating, drinking, or smoking for four hours. Following an examination for supragingival plaque (pre-brushing), they were stratified, based on their plaque scores, into two balanced groups, each of which used the two study toothbrushes in the order specified by a pre-determined randomization plan. Subjects were instructed to brush their teeth for one minute under supervision with their first assigned toothbrush and the commercially available toothpaste provided, after which they were again evaluated for supragingival plaque (post-brushing). Subjects were then dismissed from the study site, and instructed to use the home-use toothbrush and dentifrice. After three days, subjects returned to the study site for the second phase of the crossover study. Pre- and post-brushing evaluations were again performed following the same procedure, with each of the two subject groups now using the second toothbrush in the assigned treatment order. RESULTS: Of the forty-two (42) subjects entered into the study, thirty-nine (39) complied with the protocol and completed the clinical study. The results of the study indicate that the Colgate MicroSonic battery-powered toothbrush provided a statistically significant reduction in pre- to post-brushing plaque index scores of up to 52.9%. Relative to the manual toothbrush, the Colgate MicroSonic battery-powered toothbrush provided a statistically significant greater reduction in supragingival plaque scores of up to 200%. CONCLUSION: The results of this study support the conclusion that the new Colgate MicroSonic battery-powered toothbrush provides a clinically acceptable level of efficacy for the removal of supragingival plaque. Further, the Colgate MicroSonic battery-powered toothbrush exhibited significantly greater levels of efficacy for the removal of supragingival plaque when compared to the Oral-B Indicator Toothbrush.

Adult↗

PubMed1990

Trials using a crossover design and ambulatory blood pressure recordings to determine the efficacy of antihypertensive agents in individual patients.

The antihypertensive effects of the beta-blocking agent betaxolol and the calcium entry blocker verapamil were compared in a crossover single-blind trial. Seventeen patients with uncomplicated essential hypertension took either betaxolol or a slow-release formulation of verapamil for two consecutive 6-week periods. The sequence of treatment phases was randomly allocated and a 2-week washout period preceded each treatment. The antihypertensive effect of the test drugs was assessed both at the physician's office and during everyday activities using a portable blood pressure recorder. The crossover design of the trial made it possible to evaluate the antihypertensive efficacy of betaxolol and verapamil both in the group as a whole and in the individual patient. The individual patient response to one of these agents was not a reliable indicator of the same patient's response to the alternative agent. Betaxolol brought both office and ambulatory recorded blood pressures under control in a larger fraction of patients than verapamil, although the magnitude of the blood pressure fall in the responders was equal for each drug. These observations stress the need for an individualized approach to the evaluation of antihypertensive therapy. The present results also demonstrate that optimal antihypertensive therapy is still a matter of trial and error. The precise methodology that ought to characterize crossover trials may make it possible to improve the therapeutic approach to hypertensive patients.

Ambulatory Care↗

PubMed1986

The assessment of health policy changes using the time-reversed crossover design.

The time-reversed crossover design is a quasi-experimental design which can be applied to evaluate the impact of a change in health policy on a large population. This design makes use of separate sampling and analysis strategies to improve the validity of conclusions drawn from such an evaluation. The properties of the time-reversed crossover design are presented including the use of stratification on outcome in the sampling stage, which is intended to improve external validity. It is demonstrated that, although this feature of the design introduces internal validity threats due to regression toward the mean in extreme-outcome strata, these effects can be measured and eliminated from the test of significance of treatment effects. Methods for within- and across-stratum estimation and hypothesis-testing are presented which are similar to those which have been developed for the traditional two-period crossover design widely used in clinical trials. The procedures are illustrated using data derived from a study conducted by the United Mine Workers of America Health and Retirement Funds to measure the impact of cost-sharing on health care utilization among members of its health plan.

Costs and Cost Analysis↗

PubMed1988

Models of multilocus recombination: nonrandomness in chiasma number and crossover positions.

Cytological evidence indicates that genetic interference can be partitioned into two empirical components: nonrandomness in the number of chiasmata that occur and nonrandomness in the locations of multiple chiasmata. Previous studies have incorporated the first effect into genetic models for analyzing multipoint data. An extension to this approach is presented which allows for the second component of interference by modeling the probability density function of the locations of multiple crossovers. Results of reanalyses of multilocus data for the Drosophila X chromosome show that models that incorporate only the first effect give a better fit to these data than do standard mapping functions and that the extended model significantly improved the fit by decreasing the predicted frequency of multiple crossovers in nearby regions. Our results demonstrate that chiasma-based models of multilocus recombination, which are unique in incorporating direct estimates of the frequency of multiple crossovers for a chromosome region, can provide a powerful and realistic means of accounting for genetic interference when applied to the problems of gene localization, locus ordering, and exclusion mapping.

Chromosome Mapping↗

PubMed1988

Using the maximum test statistic in the two-period crossover clinical trial.

In a two-period crossover trial where residual carryover is suspected, it is often advised that first-period data only be used in an analysis appropriate for a parallel design. However, it has been shown (Willan and Pater, 1986, Biometrics 42, 593-599) that the crossover analysis is more powerful than the parallel analysis if the residual carryover, expressed as a proportion of treatment effect, is less than 2- square root of 2(1 - rho), where rho is the intrasubject correlation coefficient. Choosing between the analyses based on the empirical evaluation of this condition is equivalent to choosing the analysis with the larger corresponding test statistic. Approximate nominal significance levels are presented that maintain the desired level when basing the analysis on the maximum test statistic. Furthermore, the power and precision of the analysis based on the maximum test statistic are compared to the crossover and parallel analyses.

Clinical Trials as Topic↗

PubMedDate not supplied

Ilio-femoral and femoro-femoral crossover grafting. Analysis of an 11-year experience.

Experience with 131 crossover arterial bypass grafts for lower limb revascularization has been reviewed. Ninety-nine grafts were placed as a primary procedure for unilateral iliac artery occlusive (97) or aneurysmal (2) disease. In contrast 32 grafts were placed as a secondary procedure following the failure of a previous unilateral or bilateral conventional aorto-iliac reconstruction. Fifteen patients were not suitable for a crossover procedure without the addition of a concomitant donor limb inflow reconstruction. The one month operative mortality rate was 6.1%. The five-year cumulative patency rate was 71.4% +/- 6.0 in primary procedures and 38.1% +/- 11.3 in secondary procedures (p less than 0.05). No difference in the success rate was shown when the vein graft patency curve was compared with the synthetic graft patency curve. However, the use of a small caliber vein (6 mm or less) resulted in the lowest patency rate. No other factors affecting patency were found. This report tends to support the fact that ilio-femoral or femoro-femoral crossover bypass is a safe and effective procedure for managing unilateral iliac artery occlusive disease. With proper selection of patients, a wider use of the method is justified.

Adult↗

PubMed1980

The crossover experiment for clinical trials.

The two-period crossover or changeover design for clinical trials is compared with other simple designs in terms of statistical precision and cost. The sensitivity of the crossover to bias due to carryover effects is examined. The feasibility of using the crossover data to test for the existence of carryover effects is investigated and found to be uneconomical. A numerical example is presented.

Clinical Trials as Topic↗

PubMed1996

Design considerations in crossover trials with a single interim analysis and serial patient entry.

A two-stage sequential design is presented to facilitate a single interim analysis in crossover trials with serial patient entry. The interim analysis is based on a linear statistic that combines data from individuals observed for only one treatment period with data from those observed for both periods (Cook, R. J., 1995, Biometrics 51, 932-945). The final analysis is based on the usual test statistic used in crossover trials. The size of this procedure is controlled by partitioning the experimental type I error rate over the two analyses and deriving the appropriate critical values. We investigate the design implications of adopting this procedure over the usual analysis for crossover trials by examining the necessary sample size inflation factors to maintain power, and indicate the expected savings in terms of the number of responses required. Data from a study designed to compare two antiemetic therapies for previously untreated chemotherapy patients (Osaba, D., et al., 1986, Clinical and Investigative Medicine 9, 225-231) are used to illustrate the procedure.

Antineoplastic Agents↗

PubMed1997

Use of two-stage test statistic in the two-period crossover trials.

For two-period crossover trials where the residual carryover can only exist in the presence of treatment effect, Willan (1988, Biometrics 44, 211-218) recommended use of the maximum test statistic that chooses the analysis with the larger test statistic corresponding to the parallel analysis and the crossover analysis. We construct two alternative two-stage test procedures, based on Grizzle's approach, that maintain the actual type I error rate at the desirable level. The power, accuracy, and precision of the analysis based on the modified two-stage procedures are compared to those based on the parallel analysis, crossover analysis, and the maximum test statistic.

Biometry↗

PubMed1997

An alternative analysis for crossover studies that accounts for between-group disparities in drug response.

BACKGROUND: In crossover clinical trials comparing completely different treatments, patients tend to fall into different populations: those who respond better to treatment 1 and those who respond better to treatment 2. The correlation between treatment response in such trials is negative. The current ANCOVA analysis for crossover studies does not allow for correlations being negative, and is therefore not adequate for testing in this kind of trials. OBJECTIVE OF STUDY: To study whether matrix algebra provides a more appropriate approach for this purpose. RESULTS AND CONCLUSIONS: Using a mathematical model as well as hypothesized examples, it is demonstrated that matrix algebra of 2 pairs of cells of the same order not only allows for negative correlations in a crossover design but also provides enough power to test both the treatment and carryover effect.

Analysis of Variance↗

PubMed1997

An alternative analysis for crossover studies that accounts for between-group disparities in drug response.

BACKGROUND: In crossover clinical trials comparing completely different treatments patients tend to fall apart into different populations: those who respond better to treatment 1 and those who do so to treatment 2. The correlation between treatment response in such trials is negative. The current ANCOVA analysis for crossover studies does not allow for correlations being negative, and is, therefore, not adequate to test this kind of trial. OBJECTIVE OF STUDY: To study whether matrix algebra provides a more appropriate approach for this purpose. RESULTS AND CONCLUSIONS: Using a mathematical model as well as hypothesized examples I demonstrate that matrix algebra of 2 pairs of cells of the same order not only allows for negative correlations in a crossover design but also provides enough power to test both treatment and carryover effect.

Algorithms↗

PubMed1998

Flumazenil for hepatic coma in patients with liver cirrhosis: an Italian multicentre double-blind, placebo-controlled, crossover study.

Several factors suggest that endogenous benzodiazepines and gamma-amino-butyric acid may be involved in pathophysiology of hepatic encephalopathy (HE). Contrasting opinions exist on the therapeutic efficacy of flumazenil in the treatment of HE. This study was planned to assess the efficacy of flumazenil by a double-blind, placebo-controlled, crossover design in a large and selected population of cirrhotic patients in stage 4a HE admitted to intensive care units over a 4-year period. Out of 236 patients selected for the study, 132 received flumazenil, whereas 131 patients received placebo. Improvement of the neurological score was documented in 31 patients (23%) of flumazenil group and in two patients (1.5%) of placebo group (p < 0.001) during the first study period, whereas during the crossover period, improvement of the neurological score was documented in seven patients (5.3%) of the flumazenil group and in none of the placebo group (p = 0.022). Improvements in EEG tracings were observed in 44 patients (33.3%) of flumazenil group and in five patients (3.8%) of placebo group (p < 0.001) during the first study period; during the crossover period, improvements in EEG tracings were observed in 10 patients (7.5%) of the flumazenil group and in two patients (1.5%) of the placebo group (p = 0.040). The presence of benzodiazepines was detected in the serum of three responders and in two non-responders. The presence of diazepam and NN-desmethyl diazepam was documented in two responders; prior intake of synthetic diazepam was later confirmed in these patients. The results of our study suggest that flumazenil is beneficial only in a selected subset of cirrhotic patients with severe HE; the applicability of this treatment to unselected patients with hepatic coma or to cirrhotic patients with less severe HE still remains to be determined.

Adult↗

PubMed2025

Characterization of non-crossover recombination spectrum by single-microspore sequencing in maize and rice.

Meiotic DNA double-strand breaks (DSB) are crucial for chromosome recombination. The repair of DSB gives two outcomes: crossover (CO) and non-crossover (NCO). CO involves the bidirectional exchange between homologous chromosomes, whereas NCO refers to the unidirectional transfer of chromosome fragments. NCO can be categorized into NCO with gene conversion and NCO without gene conversion. Due to technological constraints, previous studies have focused more on CO than on NCO. In this study, we isolated single microspores from meiotic tetrads of maize (Zea mays) and rice (Oryza sativa) and conducted deep single-microspore genome sequencing to characterize NCO gene conversion (NCO-GC). Under highly stringent conditions, 101 CO and 902 NCO-GC tracts were identified in four maize tetrads, while 173 CO and 279 NCO-GC tracts were identified in six rice tetrads. In both maize and rice, NCO-GC was more prone to occur in the upstream and downstream of genes, as well as the introns. It also had a significant distribution in transposon regions. A common A-rich motif was enriched in the NCO-GC tracts of maize and rice. GC-biased gene conversion (gBGC) likely contributed to the bimodality of the GC content at the third codon position (GC3), and we discovered a significant proportional relationship between the number of DSBs and the GC content. These findings provide evidence that NCO-GC exhibits a distinct pattern compared with CO and may play an important role in gene and genome evolution.

Oryza↗