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PubMed2006

Within-plant distribution and sampling of single and mixed infestations of Bemisia tabaci and Trialeurodes vaporariorum (Homoptera: Aleyrodidae) in winter tomato crops.

In several areas of Spain, the greenhouse whitefly, Trialeurodes vaporariorum (Westwood), and the sweet potato whitefly, Bemisia tabaci (Gennadius), coexist in tomato, Lycopersicon esculentum Miller. For integrated pest management decision-making, it is important to know the abundance of each species, because they exhibit different abilities to transmit viruses, are susceptible to different biological control agents, and have different responses to insecticides. This study was conducted to provide information on the vertical distribution of T. vaporariorumn and B. tabaci in tomato plants grown in greenhouses in winter and to determine the optimal sampling unit and the sample size for estimating egg and nymphal densities of both whitefly species. Eggs of T. vaporariorum were mainly located on the top stratum of the plant, whereas B. tabaci eggs were mainly found on the middle stratum. Nymphs of both species mainly concentrated in the bottom stratum of the plant. When pest abundance and low relative variation were considered, the bottom stratum was selected as the most convenient for sampling nymphs of both whitefly species. Conversely, the same two criteria indicated that either the top or the middle strata could be used when sampling T. vaporariorum and B. tabaci eggs. Several different sampling units were compared to optimize the estimation of nymphal and egg densities in terms of cost efficiency. One disk (1.15 cm in diameter) per leaflet collected from the top stratum of the tomato plant was the most efficient sampling unit for simultaneously estimating the egg densities of the two whitefly species.

Animals↗
PubMed2003

[Male participation in contraceptive methods use].

This study aimed to evaluate male participation in the use of contraceptive methods and to identify relevant variables. A secondary data analysis was conducted, and the sample size was estimated at 175 men using contraceptives methods that require male participation. The study used the qui-square test to evaluate differences between groups, as well as multiple logistic regression analysis. Some 38% of interviewees used some birth control method that required male participation. Higher level of schooling was associated with the use of some form of contraception requiring male participation, i.e., condom use or vasectomy. Considering the sample's characteristics, the study concluded that it is possible for important changes to take place in Brazilian society with regard to the male perspective on contraception. For these changes to be possible it is necessary to invest in education for both men and women, shown to be an important factor for a balance in gender relations.

Adult↗
PubMed2001

Can placebo controls reduce the number of nonresponders in clinical trials? A power-analytic perspective.

BACKGROUND: There is ongoing debate regarding the ethics of placebo-controlled clinical trials when a moderately effective standard treatment exists. One aspect of the debate--the number of nonresponders--tends to be overlooked. A larger between-group effect size is expected in placebo-controlled trials than in trials with an active comparator. For that reason, substantially fewer subjects need to be enrolled in placebo-controlled trials; consequently, there tend to be far fewer nonresponders in placebo-controlled trials. OBJECTIVE: This analysis was undertaken to illustrate that the use of placebo as a control can reduce the number of subjects who are unnecessarily exposed to delayed treatment. METHODS: Statistical power analyses were used to estimate the sample size required to detect various population treatment differences and the resulting number of nonresponders for 2-tailed chi-square tests. RESULTS: Empiric evidence of the phenomenon is provided for a wide range of rates of response to placebo, investigational, and comparator treatments. For example, 24 subjects (ie, 12 per group) are needed to detect differences between placebo (10% response rate) and an investigational drug (70% response); 15 of these would not respond. In contrast, if the investigational drug (70% response) is initially compared with a standard therapy (60% response), 752 subjects would be required, 263 of whom would not respond. CONCLUSIONS: This paper shows empirically that placebo controls can reduce the number of nonresponders in a randomized controlled trial. The number of subjects who are exposed to unproven, albeit promising, investigational drugs should be kept to a minimum until placebo-controlled trials support their use.

Clinical Trials as Topic↗
PubMed2002

Longitudinal PET Evaluation of Cerebral Metabolic Decline in Dementia: A Potential Outcome Measure in Alzheimer's Disease Treatment Studies.

OBJECTIVE: It is well established that regional cerebral metabolic rates for glucose assessed by [(18)F]fluorodeoxyglucose (FDG) positron emission tomography (PET) in patients with Alzheimer's disease in the mental resting state (eyes and ears covered) provide a sensitive, in vivo metabolic index of Alzheimer's disease dementia. Few studies, however, have evaluated longitudinal declines in regional cerebral glucose metabolism in patients with dementia caused by Alzheimer's disease. In addition, the available studies have not used recently developed brain mapping algorithms to characterize the progression of Alzheimer's disease throughout the brain, and none considered the statistical power of regional cerebral glucose metabolism in testing the ability of treatments to attenuate the progression of dementia. METHOD: The authors used FDG PET and a brain mapping algorithm to investigate cross-sectional reductions in regional cerebral glucose metabolism, longitudinal decline in regional cerebral glucose metabolism after a 1-year follow-up, and the power of this method to evaluate treatments for Alzheimer's disease in patients with mild to moderate dementia. PET scans were initially acquired in 14 patients with Alzheimer's disease and 34 healthy comparison subjects of similar age and sex. Repeat scans were obtained in the patients 1 year later. Power analyses for voxels showing maximal decline over the 1-year period in regional cerebral glucose metabolism (mg/100 g per minute) were computed to estimate the sample sizes needed to detect a significant treatment response in a 1-year, double-blind, placebo-controlled treatment study. RESULTS: The patients with Alzheimer's disease had significantly lower glucose metabolism than healthy comparison subjects in parietal, temporal, occipital, frontal, and posterior cingulate cortices. One year later, the patients with Alzheimer's disease had significant declines in glucose metabolism in parietal, temporal, frontal, and posterior cingulate cortices. Using maximal glucose metabolism reductions in the left frontal cortex, we estimated that as few as 36 patients per group would be needed to detect a 33% treatment response with one-tailed significance of p</=0.005 and 80% power in a 1-year, double-blind, placebo-controlled treatment study. CONCLUSIONS: These findings indicate that brain metabolism as assessed by FDG PET during mental rest is a sensitive marker of disease progression in Alzheimer's disease over a 1-year period. These findings also support the feasibility of using FDG PET as an outcome measure to test the ability of treatments to attenuate the progression of Alzheimer's disease.

Aged↗
PubMed1997

Bias in meta-analysis detected by a simple, graphical test.

OBJECTIVE: Funnel plots (plots of effect estimates against sample size) may be useful to detect bias in meta-analyses that were later contradicted by large trials. We examined whether a simple test of asymmetry of funnel plots predicts discordance of results when meta-analyses are compared to large trials, and we assessed the prevalence of bias in published meta-analyses. DESIGN: Medline search to identify pairs consisting of a meta-analysis and a single large trial (concordance of results was assumed if effects were in the same direction and the meta-analytic estimate was within 30% of the trial); analysis of funnel plots from 37 meta-analyses identified from a hand search of four leading general medicine journals 1993-6 and 38 meta-analyses from the second 1996 issue of the Cochrane Database of Systematic Reviews. MAIN OUTCOME MEASURE: Degree of funnel plot asymmetry as measured by the intercept from regression of standard normal deviates against precision. RESULTS: In the eight pairs of meta-analysis and large trial that were identified (five from cardiovascular medicine, one from diabetic medicine, one from geriatric medicine, one from perinatal medicine) there were four concordant and four discordant pairs. In all cases discordance was due to meta-analyses showing larger effects. Funnel plot asymmetry was present in three out of four discordant pairs but in none of concordant pairs. In 14 (38%) journal meta-analyses and 5 (13%) Cochrane reviews, funnel plot asymmetry indicated that there was bias. CONCLUSIONS: A simple analysis of funnel plots provides a useful test for the likely presence of bias in meta-analyses, but as the capacity to detect bias will be limited when meta-analyses are based on a limited number of small trials the results from such analyses should be treated with considerable caution.

Bias↗
PubMed1999

[The vision distribution and causes of blindness in elderly population in Doumen county].

OBJECTIVE: To investigate the vision distribution and the leading cause of blindness in farmer aged >or= 50 years in Doumen county. METHODS: Cluster sampling size was estimated within an error bound of 0.35% with 95% confidence limit, 1.25 design effect and 85% response rate. Presenting visual acuity was measured by ETDRS (early treatment diabetic retinopathy study) tumbling chart. Eye examinations of external eye, anterior chamber, lens, fundus and intraocular pressure were carried out by ophthalmologists. A diagnosis of the principal cause for all the eyes with presenting visual acuity less than 0.3 was made as well. The field survey was conducted by two teams after pilot agreement testing. RESULT: 5,342 individuals were examined in 36 sampling units. The prevalence of blindness was five-fold in the group aged >or= 70 years than in the group 50 - 59 years. The rate of blindness in the group with less education was higher than the group with 5 years schooling. The leading causes of blindness were cataract (44.90%), cornea opacity (16.36%), globe disorders (10.76%), refractive error (7.08%) and glaucoma (5.88%). CONCLUSIONS: The prevalence of blindness and low vision was 2.67% and 19.91%, respectively in farmers aged >or= 50 years. The leading cause of blindness was cataract.

Age Distribution↗
PubMed1997

Estimating the size of a population from a single sample: methodology and practical issues.

In contrast to classical capture recapture methods, the single-sample method of Laska, Meisner, and Siegel (1988) (LMS) enables estimation of the size of a population, N*, on the basis of a single survey. For example, it may be desired to estimate the unduplicated number of individuals served by a mental health center during the last year on the basis of a 1-week sample. The time since each of the sampled individuals last engaged in the activity that defines the population is ascertained. The LMS estimator of N* and its unbiasedness property are motivated in a simple way, and an improved LMS estimator is introduced if additional information is available. An empirical assessment of the procedure is made using mental health service data for which the true population size is known. The performance of the extended LMS estimator is a substantial improvement over the standard LMS estimator.

Bias↗
PubMed1992

Assessing the responsiveness of a quality-of-life instrument and the measurement of symptom severity in essential hypertension.

A pilot study was conducted to compare symptoms elicited with an open-ended question versus a checklist and to measure the responsiveness of quality-of-life measures to symptom severity. The pilot study was part of a multicentre, randomised, double-blind, placebo-controlled study of clentiazem, a calcium channel blocker, in the treatment of essential hypertension. Symptom and quality-of-life data were obtained from 88 patients at baseline and after 10 weeks of therapy by a trained telephone interviewer. Comparison of the symptom checklist and open-ended question method suggests that both methods are necessary to capture severe symptomatology. The 24-item checklist failed to elicit approximately 50% of the severe symptoms reported on the open question list. On the other hand, only 18% of the most severe symptoms subsequently reported on the checklist were first reported by the open question method. The responsiveness of quality-of-life measures to symptom severity was tested using a 20% change in symptom severity obtained from the checklist as the minimal clinically significant difference. Using Guyatt's formula, a minimum sample size of approximately 428 (alpha = 0.05, beta = 0.10) patients per treatment group is required to detect differences in measures of general health perception, anxiety, depression and limitations in social activities. A larger sample is required to show differences in leisure activities. Differences in limitations of the capability to perform house or yard work might be demonstrable with as few as 17 patients per group. This pilot study demonstrated that the severity of symptoms associated with hypertension, and the side effects of its treatment with drugs, are adequately captured by a symptom checklist preceded by an open-ended method of questioning. Responsiveness testing estimated the sample size required to show a statistically significant difference, assuming a 20% change in symptom severity.

Diltiazem↗
PubMed2025

Assessing data size requirements for training generalizable sequence-based TCR specificity models via pan-allelic MHC-I point-mutation ligandome evaluation.

Rapid identification of T cell receptors (TCRs) that specifically bind patient-unique neoepitopes is a critical challenge for personalized TCR-based therapies in oncology. Due to enormous diversity of both TCR and neoepitope repertoires, a machine learning predictor of TCR-pMHC specificity for personalized therapy must generalize to TCRs and epitopes not seen in the training data. We estimate the necessary size of such training data. We first confirm that published models fail to generalize beyond a single-residue dissimilarity to the epitope training set distribution. We then impute the point-mutation ligandome across the 34 most prevalent human MHC alleles and represent it as a graph based on our established dissimilarity cutoff. By finding the dominating set of this graph, we estimate that between one and 100 million epitopes are required to train a generalizable sequence-based TCR specificity prediction model-1000 times the size of current public data.

Humans↗
PubMed2006

Adaptive, group sequential and decision theoretic approaches to sample size determination.

This paper presents two adaptive methods for sample size re-estimation within a unified group sequential framework. The conceptual and practical distinction between these adaptive modifications and more traditional sample size changes due to revised estimates of nuisance parameters is highlighted. The motivation for the adaptive designs is discussed. Having established that adaptive sample size modifications can be made without inflating the type 1 error, the paper concludes with a novel decision theoretic approach for determining the magnitude of the sample size modification.

Clinical Trials as Topic↗
PubMed1997

A study of the effects of exposure on cleanup workers at the Chernobyl nuclear reactor accident using multiple end points.

Blood samples were collected from 192 exposed workers who participated in the cleanup after the April 26, 1986, nuclear reactor accident at Chernobyl, Ukraine. These samples, together with samples from 73 individuals living in Russia but not involved in Chernobyl cleanup activities, were collected during September 1991 to May 1996 and shipped to the U.S. for evaluation by three bioassays: cytogenetic analysis based on chromosome painting, HPRT mutation analysis and glycophorin A (GPA) variant analysis. Univariate statistical analyses of the results of each bioassay (including adjustments for age, smoking status and estimated precision of the bioassay) found greater frequencies of chromosome translocations and HPRT mutant T lymphocytes among the exposed individuals compared to the controls (P < or = 0.01). GPA analyses showed no significant difference for exposed compared to controls for either hemizygous, N/O, or homozygous, N/N, variant cell frequency. Multivariate analysis of variance of the subset of 44 exposed and 14 unexposed individuals with measurements from all three bioassays found elevated frequencies of chromosomal translocations and HPRT mutants, and reduced frequencies for both GPA end points among the exposed persons compared to the controls. However, none of these differences, considered singly or in combination, was statistically significant (although statistical power is low due to small sample sizes). Mean estimated dose, based on cytogenetic response, for those exposed was 9 cGy (range 0 to 51 cGy) and was less than that estimated by physical dosimetry (25 cGy). Correlation between the end points of the bioassays and estimated physical dosimetry was low (r < 0.2); the only significant correlation found was for physical dose estimate and dates worked at Chernobyl (r = 0.4, P < 0.01), with those working soon after the accident receiving greater estimated doses.

Adolescent↗
PubMed1997

Randomised controlled trial of anterior-chamber intraocular lenses.

BACKGROUND: There are an estimated 16 million people blind in both eyes with cataracts. Most live in rural areas of developing countries where surgical resources are scarce. There is no consensus on the most appropriate type of intraocular lens in situations where high-volume low-cost surgery is required. This study was undertaken to evaluate the safety of multiflex open-loop anterior-chamber lenses (ACIOLs). METHODS: 2000 people attending Lahan Eye Hospital, southern Nepal, with bilateral cataracts reducing vision to 6/36 or less were randomly allocated to receive standard surgery--intracapsular extraction (ICCE) with aphakic correction--or ICCE with an ACIOL in their first operated eye. The primary outcome was a visual acuity of less than 6/60 in the operated eye at 1 year follow-up. Visual acuity was measured for 91% of the cohort at 1 year. The sample size was estimated to detect a doubling in poor visual outcome from an estimated rate of 4% in the standard surgery (control) group. FINDINGS: The median (range) time taken to do the surgery was 6.0 (3.0-17.2) min for the ACIOL group and 4.1 (2.4-10.3) min for the control group. 1 year after surgery, 5.0% of the ACIOL group and 5.4% of controls had functional vision less than 6/60 (OR 0.93 [0.60-1.43], p = 0.71). The causes of poor vision in the ACIOL and control groups were: correctable refractive error (22 and 29), uveitis/secondary glaucoma (13 and two), endophthalmitis (four and seven), pre-existing eye disease (four and five), retinal detachment (none and four), cystoid macular oedema (two and none), corneal ulcer (one and one), and corneal decompensation (none and one). INTERPRETATION: This study provides evidence that, in rural areas of developing countries, multiflex open-loop ACIOLs can be implanted safely by experienced ophthalmologists after routine ICCE, avoiding the disadvantages of aphakic spectacle correction. Further follow-up is planned.

Anterior Chamber↗
PubMed1994

A randomized trial comparing perioperative chemotherapy and surgery with surgery alone in resectable stage IIIA non-small-cell lung cancer.

BACKGROUND: Patients with resectable stage IIIA non-small-cell lung cancer have a low survival rate following standard surgical treatment. Nonrandomized trials in which induction chemotherapy or a combination of chemotherapy and radiation prior to surgery were used to treat patients with regionally advanced primary cancers have suggested that survival is improved when compared with treatment by surgery alone. PURPOSE: We performed a prospective, randomized study of patients with previously untreated, potentially resectable clinical stage IIIA non-small-cell lung cancer to compare the results of perioperative chemotherapy and surgery with those of surgery alone. METHODS: This trial was designed to test the null hypothesis that the proportion of patients surviving 3 years is 12% for either treatment group against the alternate hypothesis that the 3-year survival rate would be 12% in the surgery alone group and 32% in the perioperative chemotherapy group. The estimated required sample size was 65 patients in each group. The trial was terminated at an early time according to the method of O'Brien and Fleming following a single unplanned interim analysis. The decision to terminate the trial was based on ethical considerations, the magnitude of the treatment effect, and the high degree of statistical significance attained. In total, 60 patients were randomly assigned between 1987 and 1993 to receive either six cycles of perioperative chemotherapy (cyclophosphamide, etoposide, and cisplatin) and surgery (28 patients) or surgery alone (32 patients). For patients in the former group, tumor measurements were made before each course of chemotherapy and the clinical tumor response was evaluated after three cycles of chemotherapy; they then underwent surgical resection. Patients who had documented tumor regression after preoperative chemotherapy received three additional cycles of chemotherapy after surgery. RESULTS: After three cycles of preoperative chemotherapy, the rate of clinical major response was 35%. Patients treated with perioperative chemotherapy and surgery had an estimated median survival of 64 months compared with 11 months for patients who had surgery alone (P < .008 by log-rank test; P < .018 by Wilcoxon test). The estimated 2- and 3-year survival rates were 60% and 56% for the perioperative chemotherapy patients and 25% and 15% for those who had surgery alone, respectively. CONCLUSIONS: In this trial, the treatment strategy using perioperative chemotherapy and surgery was more effective than surgery alone. IMPLICATIONS: This clinical trial strengthens the validity of using perioperative chemotherapy in the management of patients with resectable stage IIIA non-small-cell lung cancer. Further investigation of the perioperative chemotherapy strategy in earlier stage lung cancer is warranted.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1998

Adaptations of the masticatory system after bilateral fractures of the mandibular condylar process.

PURPOSE: The objective of this investigation was to evaluate the adaptations that occur in the masticatory system after treatment of bilateral fractures of the mandibular condylar process. PATIENTS AND METHODS: Twenty-two patients (15 men and seven women) with bilateral condylar process fractures treated by open reduction and rigid internal fixation (n = 6), closed therapy (n = 14), or a combination of these techniques (n = 2) were compared with 22 sex- and age-matched controls. Measures of mandibular range of motion, bite force, muscle activity, estimated joint forces, and skeletal morphology were determined at 6 weeks, 6 months, and 1, 2, and 3 years after treatment in all subjects. Various statistical tests were used for comparing differences between patients and controls. RESULTS: There was no significant difference in the patients' morphologic measures for the open and closed reduction procedures; therefore, all of these patients were tested as a single group. After treatment, patients had significantly increased mandibular plane and gonial angles and decreased facial axis angles. They also showed a significant reduction in posterior facial height and moment arm length for the masseter and pterygoid muscles. Anterior and posterior temporalis muscle direction also was significantly different between patients and controls. Patients had significantly limited mobility during the first year after fracture. Bite forces were lower for patients at all times and tooth positions, with a significant difference at 6 weeks after treatment. Patients had a tendency to use proportionally higher temporalis muscle activity during maximum biting; however, the differences were not statistically significant, probably because of the small sample size. The estimated joint force magnitudes were essentially identical between patients and controls; however, the direction of the patients' joint forces were more posteriorly directed for both incisor and molar bites. CONCLUSION: The results of this study suggest that early reduction in mandibular range of motion, bite force, and the distribution of masticatory muscle activity assist in preventing overloading of the bilaterally fractured mandibular condylar processes.

Adaptation, Physiological↗
PubMed1995

Optimal experimental design and sample size for the statistical evaluation of data from somatic mutation and recombination tests (SMART) in Drosophila.

In genetic toxicology it is important to know whether chemicals should be regarded as clearly hazardous or whether they can be considered sufficiently safe, which latter would be the case from the genotoxicologist's view if their genotoxic effects are nil or at least significantly below a predefined minimal effect level. A previously presented statistical decision procedure which allows one to make precisely this distinction is now extended to the question of how optimal experimental sample size can be determined in advance for genotoxicity experiments using the somatic mutation and recombination tests (SMART) of Drosophila. Optimally, the statistical tests should have high power to minimise the chance for statistically inconclusive results. Based on the normal test, the statistical principles are explained, and in an application to the wing spot assay, it is shown how the practitioner can proceed to optimise sample size to achieve numerically satisfactory conditions for statistical testing. The somatic genotoxicity assays of Drosophila are in principle based on somatic spots (mutant clones) that are recovered in variable numbers on individual flies. The underlying frequency distributions are expected to be of the Poisson type. However, some care seems indicated with respect to this latter assumption, because pooling of data over individuals, sexes, and experiments, for sample, can (but need not) lead to data which are overdispersed, i.e., the data may show more variability than theoretically expected. It is an undesired effect of overdispersion that in comparisons of pooled totals it can lead to statistical testing which is too liberal, because overall it yields too many seemingly significant results. If individual variability considered alone is not in contradiction with Poisson expectation, however, experimental planning can help to minimise the undesired effects of overdispersion on statistical testing of pooled totals. The rule for the practice is to avoid disproportionate sampling. It is recalled that for optimal power in statistical testing, it is preferable to use equal total numbers of flies in the control and treated series. Statistical tests which are based on Poisson expectations are too liberal if there is overdispersion in the data due to excess individual variability. In this case we propose to use the U test as a non-parametric two-sample test and to adjust the estimated optimal sample size according to (i) the overdispersion observed in a large historical control and (ii) the relative efficiency of the U test in comparison to the t test and related parametric tests.

Animals↗
PubMedDate not supplied

Sickle cell anaemia trial.

The major cause of death in sickle cell anaemia is from infection, especially infection caused by Streptococcus pneumoniae. Meningitis, pneumonia and septicaemia caused by this organism are the primary types of infection leading to death. Children under three years of age are at highest risk. We have known for over twenty years that approximately 30 per cent of the infants born with sickle cell anaemia will become infected in the first three years of life and one-third can be expected to die from the infection. These data were the reason that we conducted the Prophylactic Penicillin Study (PROPS), a trial to investigate the effectiveness of oral prophylactic penicillin in preventing severe infection due to S. pneumoniae. This investigation was a very efficient, cost effective study because of its timeliness and its conduct within the framework of an ongoing study. Moreover, the question being answered was simple and focused with up-to-date data that permitted accurate estimates of sample size and incidence.

Anemia, Sickle Cell↗
PubMed1984

The SCE test as a tool for cytogenetic monitoring of human exposure to occupational and environmental mutagens.

The sister chromatid exchange (SCE) test system using human peripheral lymphocytes is proposed as a valuable tool for the cytogenetic monitoring of exposure to potential chemical mutagens in the occupational environment. We examined the SCE frequencies in organic solvent-exposed workers and reviewed the effects of occupational and environmental chemicals on SCE frequencies. The results obtained in these exposed populations are rather contradictory, which may be related to confounding factors, such as personal life style (smoking, drinking, and drugs) of the examinees, tissue culture conditions and the number of subjects examined. We discussed some practical problems for exposure estimation and sample size determination and are led to the following conclusions. 1) The possible combined effects of potential mutagens and cigarette smoking should be taken into consideration when using the SCE test system. 2) Cell cycle kinetic analysis by differential chromatid staining would provide valuable information as a biological indicator for the monitoring of the workers exposed to xenobiotics. 3) By appropriately setting the number of examinees, monitoring would become more efficient in detecting an increased SCE frequency in the exposed populations. Further studies are also required to enhance the sensitivity of the SCE test system for monitoring purposes.

Benzene↗
PubMed2001

Converted laparoscopic colorectal surgery.

BACKGROUND: Conversion rates following laparoscopic colorectal surgery vary widely between studies, and the outcome of converted patients remains controversial. METHODS: A comprehensive search of the English-language literature was updated until May 1999. RESULTS: Twenty-eight studies on 3232 patients were considered for analysis. The overall conversion rate was 15.38%. Seventy nine percent of the studies did not include a definition for conversion; in these studies, the conversion rate was significantly lower than in the series where a specific definition was considered (13.7% vs 18.9%, chi-square test, p < 0.001). Converted patients had a prolonged hospital stay (11.38 vs 7.41 days) and operative time (209 vs 189 min) in comparison with laparoscopically completed patients (95% confidence interval (CI), 1.70-4.00 and 35.90-37.10, respectively). The factors associated with an increased rate for conversion were left colectomy (Odds Ratio [OR] = 1.061), anterior resection of the rectum (OR = 1.088), diverticulitis (OR = 1.302), and cancer (OR = 2.944) (for each parameter, Wald chi-square value, p < 0.001). CONCLUSIONS: In nonrandomized studies, the rate of laparoscopically completed colorectal resections is close to 85%. Because converted patients have a distinct outcome, a clear definition of conversion is required to compare the results of randomized trials. Such trials should also consider a 20% rate of conversion when estimating the sample size for the desired power level. It is likely that converted patients will have a significant impact on the results of future clinical research in laparoscopic colorectal surgery.

Aged↗