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PubMed1997

Incorporation of sequential trials into a fixed effects meta-analysis.

The technique of meta-analysis provides a systematic and quantitative approach to the summary of results from a collection of similar randomized studies. Comprehensive methodology exists for analysis when all trials are of a fixed sample size design, but this is based on assumptions which are no longer valid when incorporating sequentially designed studies. In this paper the effect of incorporating one or more sequential trials into a meta-analysis otherwise consisting of fixed sample size trials is investigated. The results from simulation studies of a variety of plausible scenarios are presented. The aim is to quantify the extent to which bias is introduced. It was found that when incorporating two alternative sequential designs, the triangular test and the O'Brien and Fleming procedure, the results of a conventional meta-analysis remain accurate.

Bias↗
PubMed1978

The importance of beta, the type II error and sample size in the design and interpretation of the randomized control trial. Survey of 71 "negative" trials.

Seventy-one "negative" randomized control trials were re-examined to determine if the investigators had studied large enough samples to give a high probability (greater than 0.90) of detecting a 25 per cent and 50 per cent therapeutic improvement in the response. Sixty-seven of the trials had a greater than 10 per cent risk of missing a true 25 per cent therapeutic improvement, and with the same risk, 50 of the trials could have missed a 50 per cent improvement. Estimates of 90 per cent confidence intervals for the true improvement in each trial showed that in 57 of these "negative" trials, a potential 25 per cent improvement was possible, and 34 of the trials showed a potential 50 per cent improvement. Many of the therapies labeled as "no different from control" in trials using inadequate samples have not received a fair test. Concern for the probability of missing an important therapeutic improvement because of small sample sizes deserves more attention in the planning of clinical trials.

Clinical Trials as Topic↗
PubMed1995

Influence of a sampling review process for radiation oncology quality assurance in cooperative group clinical trials--results of the Radiation Therapy Oncology Group (RTOG) analysis.

The Radiation Therapy Oncology Group (RTOG) designed a random sampling process and observed its influence upon radiotherapy review mechanisms in cooperative group clinical trials. The method of sampling cases for review was modeled from sampling techniques commonly used in pharmaceutical quality assurance programs, and applied to the initial (on-study) review of protocol cases. 'In control' (IC) status is defined for a given facility as the ability to meet minimum compliance standards. Upon achieving IC status, activation of the sampling process was linked to the rate of continued patient accrual for each participating institution in a given protocol. The sampling design specified that > or = 30% cases not in compliance would be detected with 80% power. A total of 458 cases was analyzed for initial review findings in four RTOG Phase III protocols. Initial review findings were compared with retrospective (final) review results. Of the 458 cases analyzed, 370 underwent initial review at on-study, while 88 did not require review as they were enrolled from institutions that had demonstrated protocol compliance. In the group that had both initial and final review, 345/370 (93%) were found to have followed the protocol or had a minor variation. Of the exempted cases, 79/88 (90%) were found to be per protocol or a minor variant. The sampling process proved itself to be cost-effective and resulted in a noticeable reduction in the workload, thus providing an improved approach to resource allocation for the group. Continued evaluation of the sampling mechanism is appropriate as study designs and participants vary over time, and as more data become available to study.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical Protocols↗
PubMed1991

Distribution and sampling of Aedes taeniorhynchus (Diptera: Culicidae) eggs in a Florida mangrove forest.

The distribution of Aedes taeniorhynchus (Wiedemann) eggs in a Florida mangrove basin forest was quantified and used to design a sampling plan. Eggs were found in detritus-rich soil with the highest densities in a band at elevations 0.1-0.2 m above the water line. Dispersion indices (k and Taylor's b) indicated that the eggs were aggregated; 14 of 16 populations tested fit the negative binomial distribution. A fixed-size sampling plan using systematic sampling was designed from these data.

Aedes↗
PubMed2003

Using a quasi-experimental research design to assess knowledge in continuing medical education programs.

INTRODUCTION: The objectives of continuing medical education (CME) programs include knowledge acquisition, skill development, clinical reasoning and decision making, and health care outcomes. We conducted a year-long medical education research study in which knowledge acquisition in our CME programs was assessed. METHOD: A randomized separate-sample pretest/past-test design, a quasi-experimental technique, was used. Nine CME programs with a sufficient number of participants were identified a priori. Knowledge acquisition was compared between the control group and the intervention group for the nine individual programs and for the combined programs. RESULTS: A total of 667 physicians, nurses, and other health professionals participated. Significant gain in knowledge was found for six programs: Perinatology, Pain Management, Fertility Care 2, Pediatrics, Colorectal Diseases, and Alzheimer's Disease (each p < .001). Also, the intervention group differed from the control group when the nine programs were combined (p < .001), with an effect size of .84. DISCUSSION: The use of sound quasi-experimental research methodology (separate-sample pretest/post-test design), the inclusion of a representative sample of CME programs, and the analysis of nearly 700 subjects led us to have confidence in concluding that our CME participants acquired a meaningful amount of new knowledge.

Education, Medical, Continuing↗
PubMed1985

Social disability in schizophrenia: the controlled prospective Burghölzli study. I. Case-finding, research design, and characteristics of samples.

The Psychiatric University Hospital Zürich (Burghölzli') is taking part in the 'WHO Collaborative Study on the Assessment and Reduction of Psychiatric Disability'. This multicenter project aims to assess the development of social disability for schizophrenic psychoses of relatively recent onset. This paper provides a brief review of underlying concepts, the prospective procedure, and the screening criteria applying to all centers. The research team at 'Burghölzli' has greatly extended the general design. Apart from the "obligatory" assessment of 69 first admitted schizophrenics (initial assessment on first hospitalization or outpatient treatment and follow-ups after 1, 2, and 5 years) we have also interviewed a control sample of 60 healthy persons (including a 2-year follow-up) and an 'extreme' sample of 46 chronic schizophrenic outpatients legally entitled to disability pension. Moreover, we have used several supplementary assessment instruments. This paper is to discuss the purpose of our extended research design. All cohorts are described with respect to screening criteria, sampling procedure, and some basic characteristics; furthermore, a review is given of the additional assessment instruments. It is intended to provide basic information for subsequent papers dealing with results from the study.

Adult↗
PubMed2003

Survey for hydatidosis in cattle bred in the northern region of the Northern Territory of Australia.

OBJECTIVE: To determine whether hydatidosis occurs in cattle bred in the northern region of the Northern Territory. DESIGN: A survey utilising two stage sampling was designed to provide 95% confidence of detecting hydatids in cattle with a herd prevalence of 10% and animal prevalence of 10%. PROCEDURE: For a 1 year abattoir killing season, lesions from the liver and/or lung were collected from 4348 cattle being slaughtered at a Northern Territory abattoir and examined for hydatid cysts. The origin of cattle was established through identification of the brand. RESULTS: Sample sizes of 41 or more Northern Territory bred cattle were achieved for each of 29 properties. No hydatid cysts were found in cattle bred in the northern region of the Northern Territory. CONCLUSION: This study provides evidence that a cycle of hydatid transmission does not occur in the northern region of the Northern Territory.

Abattoirs↗
PubMed2003

Misrepresenting random sampling? A systematic review of research papers in the Journal of Advanced Nursing.

AIM: This paper discusses the theoretical limitations of the use of random sampling and probability theory in the production of a significance level (or P-value) in nursing research. Potential alternatives, in the form of randomization tests, are proposed. BACKGROUND: Research papers in nursing, medicine and psychology frequently misrepresent their statistical findings, as the P-values reported assume random sampling. In this systematic review of studies published between January 1995 and June 2002 in the Journal of Advanced Nursing, 89 (68%) studies broke this assumption because they used convenience samples or entire populations. As a result, some of the findings may be questionable. DISCUSSION: The key ideas of random sampling and probability theory for statistical testing (for generating a P-value) are outlined. The result of a systematic review of research papers published in the Journal of Advanced Nursing is then presented, showing how frequently random sampling appears to have been misrepresented. Useful alternative techniques that might overcome these limitations are then discussed. REVIEW LIMITATIONS: This review is limited in scope because it is applied to one journal, and so the findings cannot be generalized to other nursing journals or to nursing research in general. However, it is possible that other nursing journals are also publishing research articles based on the misrepresentation of random sampling. The review is also limited because in several of the articles the sampling method was not completely clearly stated, and in this circumstance a judgment has been made as to the sampling method employed, based on the indications given by author(s). CONCLUSION: Quantitative researchers in nursing should be very careful that the statistical techniques they use are appropriate for the design and sampling methods of their studies. If the techniques they employ are not appropriate, they run the risk of misinterpreting findings by using inappropriate, unrepresentative and biased samples.

Data Collection↗
PubMed2006

A brief review on software developments for group sequential and adaptive designs.

In this paper the currently available software we know for group sequential and adaptive designs is briefly reviewed. Stand-alone packages as well as modules within software packages or programming languages exist. New software developments for adaptive designs enable the user to perform data dependent design adaptations while controlling the Type I error rate.

Biometry↗
PubMed1986

Biostatistical issues and concepts in epidemiologic research.

This paper describes recent developments in failure time regression, and the application of such methods to epidemiologic data. Relative risk and odds ratio estimation procedures are described under cohort and case-control sampling, and under some less standard designs for sampling within a cohort. Some special issues that arise in the analysis of vital data are also mentioned. While methods for descriptive analyses are emphasized some attention is also given to mechanistic models for carcinogenesis and their uses. Topics meriting further methodologic development are delineated throughout.

Epidemiology↗
PubMed2004

Concentration of ochratoxin A in wines from supermarkets and stores of Valencian Community (Spain).

Ochratoxin A (OTA) is a mycotoxin produced by fungi species belonging to the genera Aspergillus and Penicillium being isolated in alcoholic beverages. The aim of this work is developed and applied a procedure for the analysis of OTA in wines. An analytical method based on immunoaffinity column (IAC) for clean-up, liquid chromatography with fluorescence detection (LC-FD), and LC-FD after of OTA methylation was used to determine the occurrence of OTA in wines. Recoveries of this mycotoxin spiked to red wines at 0.5 ng/ml level were >90% with an average of relative standards deviations of 4%. Furthermore, 116 wine samples from designation of origin (DO) and three samples from food stores of Valencian Community (Spain) were examined for the occurrence of OTA being the levels of this mycotoxin ranged from <0.01 to 0.76 ng/ml. Finally, the estimated daily intake of OTA in this study was 0.15 ng/kg bw per day.

Chromatography, Liquid↗
PubMed2005

Parvovirus B19 viral loads in relation to VP1 and VP2 antibody responses in diagnostic blood samples.

BACKGROUND: Human parvovirus B19 infection is characterised by high peak viral load levels followed by episodes of prolonged viremia. The risk of transmission of parvovirus B19 by blood or blood products has been increasingly recognised and parameters that can predict the risk of transmission are subject of interest. OBJECTIVES: This study aimed to study correlations between B19 viral DNA loads and antibody responses to the viral antigens VP1 and VP2 in clinical serum samples. STUDY DESIGN: A panel of 1610 serum samples from patients clinically suspected from acute B19 infection were analysed. Antibodies were measured by the parvovirus anti-VP1 immuno-fluorescence assay (IFA) and the anti-VP2 enzyme immunoassay (EIA) from Biotrin. B19 viral loads were measured by a real-time PCR using the external WHO standard for DNA quantification. RESULTS: Positive IgM responses were found in 154 (9.6%) of the 1610 sera tested. Based on the PCR results in a subset of 312 sera, the anti-VP2 EIA IgM showed a better combination of sensitivity/specificity (91%/94%) compared to the anti-VP1 IFA (66%/97%). B19 DNA levels in the sera strongly correlated with the levels of IgM antibodies, all sera with high viral loads (>10(6)IU/ml) having VP2 EIA IgM ratios above 3.0. CONCLUSIONS: The B19 VP2 IgM ELISA is superior to the B19 VP1 IgM IFA if verified by PCR. Anti-VP2 IgM antibodies in sera are indicative for the presence B19 DNA and can be used to predict high levels of B19 DNA in diagnostic sera.

Adolescent↗
PubMed2003

Miniaturized sample preparation combined with liquid phase separations.

Miniaturized sample preparation methods designed as the sample pretreatment for liquid phase separations, such as liquid chromatography, capillary electrophoresis and capillary electrochromatography, have been reviewed especially for the on-line coupling of the sample preparation process and the separation process. The development of the desorption interfaces for the effective combining of the sample preparation and subsequent liquid phase separations is briefly described along with the applications of the combined analytical systems to the analysis of complex sample mixtures such as biological and environmental matrices. Novel use of fine polymeric filaments as the extraction medium for microscale liquid phase separation methods are investigated and a comparison is made with other sample preparation techniques. Polymer coating onto the fibrous material is also introduced to further develop microscale sample preparation methods with improved extraction performance. Several other microscale sample preparation methods having a potential compatibility to the liquid phase separations are also described for future applications of these techniques.

Chromatography, Liquid↗
PubMed2003

Quality control measures for the serological diagnosis of hantavirus infections.

BACKGROUND: With society's rapidly increasing mobility, patients infected with severe viral infections can become seriously ill at any place in Europe and elsewhere. Improving the diagnostics of these infections is the most important step in detecting the pathogens and dealing with them, and for this purpose, quality control measures are essential tools. OBJECTIVES: To assess the diagnostic reality for rare hantavirus infections in Europe by (1) running a pre-evaluation panel (four samples, sent out in 1999) to optimise sample preparation and shipping procedure and afterwards (2) starting an External Quality Assurance (EQA) program (20 samples, sent out in 2001). STUDY DESIGN: All samples sent out had to be tested for the presence of specific IgG and IgM antibodies against hantavirus. For the pre-evaluation panel, four samples were distributed (two samples IgG+/IgM-, one sample IgG-borderline/IgM-, one sample IgG-/IgM-), for the EQA 20 samples (six samples IgG+/IgM+, eight samples IgG+/IgM-, one sample IgG-borderline/IgM-, five samples IgG-/IgM-). Thirteen laboratories took part in the pre-evaluation panel, 18 laboratories participated in the first EQA run. RESULTS: For the pre-evaluation panel, the participants reported correct results for 64% of the IgG-positive samples (85% excluding borderline-positive sample), and 92% for the IgG-negative sample. IgM testing was correctly negative in all laboratories. For the EQA, the participants reported correct results for 76% of the IgG-positive samples, and 97% correct results for the IgG-negative samples. For the IgM-positive samples, 53% correct results were reported, and 98% correct results for the IgM-negative samples. CONCLUSIONS: The results presented here prove the importance of quality measures also for viruses only rarely suspected, like hantavirus, and they clearly demonstrate the need for improvement of the existing test systems.

Antibodies, Viral↗
PubMed1998

Improved sensitivity of astrovirus-specific RT-PCR following culture of stool samples in CaCo-2 cells.

BACKGROUND: During an epidemiological study on the incidence of astrovirus infection in children hospitalized with acute gastroenteritis, a Northern hybridization method was used to screen stool samples for astrovirus RNA. Positive results were confirmed using reverse transcriptase-polymerase chain reaction (RT-PCR), which showed surprisingly low sensitivity. The low sensitivity of the RT-PCR method was considered likely to be due to the presence of non-specific inhibitors. OBJECTIVE: To develop and use a simple culture method to improve the sensitivity of diagnosis of astrovirus in clinical stool samples using RT-PCR. STUDY DESIGN: Stool samples from children hospitalized with acute gastroenteritis were screened for astrovirus using Northern hybridization. The presence of astrovirus RNA was then confirmed using an astrovirus-specific RT-PCR. Hybridization positive samples that failed to generate an RT-PCR product were cultured in CaCO-2 cells for 48 h. RNA was isolated from cultures and re-tested using the same RT-PCR method. RESULTS: Using Northern hybridization, human astroviruses were detected in the stools of 31 patients and confirmed by RT-PCR in 16 samples. RNA extracted directly from 15 faecal specimens could not be amplified by RT-PCR. After culture for 48 h in CaCO-2 cells, RNA extracted from these samples could be amplified and confirmed the presence of astrovirus in all 15 specimens. CONCLUSIONS: Development of a simplified culture method for astrovirus positive faecal specimens improved the sensitivity of astrovirus-specific RT-PCR from 52 to 100%. The technique should be of value as a confirmatory test in surveys of human astrovirus infection.

Astroviridae Infections↗
PubMed2003

High-throughput nuclear magnetic resonance analysis using a multiple coil flow probe.

An automated method for high-throughput nuclear magnetic resonance (NMR) spectroscopy has been developed using a four-coil Multiplex NMR probe. The probe is constructed with solenoidal microcoils optimized for detection of small volume, mass-limited samples and a flow-through design. Four samples can be simultaneously injected into the Multiplex probe with a robotics liquid handler and then analyzed in rapid succession using a selective excitation experiment. Due to the simultaneous injection of four samples and the reduced analysis time with rapid selective excitation, the analysis rate achieved thus far is as low as 1 sample/34 s for 1D 1H NMR.

Magnetic Resonance Spectroscopy↗
PubMed2005

Characterization of urban pollutant emission fluxes and ambient concentration distributions using a mobile laboratory with rapid response instrumentation.

A large and increasing fraction of the planet's population lives in megacities, especially in the developing world. These large metropolitan areas generally have very high levels of both gaseous and particulate air pollutants that have severe impacts on human health, ecosystem viability, and climate on local, regional, and even continental scales. Emissions fluxes and ambient pollutant concentration distributions are generally poorly characterized for large urban areas even in developed nations. Much less is known about pollutant sources and concentration patterns in the faster growing megacities of the developing world. New methods of locating and measuring pollutant emission sources and tracking subsequent atmospheric chemical transformations and distributions are required. Measurement modes utilizing an innovative van based mobile laboratory equipped with a suite of fast response instruments to characterize the complex and "nastier" chemistry of the urban boundary layer are described. Instrumentation and measurement strategies are illustrated with examples from the Mexico City and Boston metropolitan areas. It is shown that fleet average exhaust emission ratios of formaldehyde (HCHO), acetaldehyde (CH3CHO) and benzene (C6H6) are substantial in Mexico City, with gasoline powered vehicles emitting higher levels normalized by fuel consumption. NH3 exhaust emissions from newer light duty vehicles in Mexico City exceed levels from similar traffic in Boston. A mobile conditional sampling air sample collection mode designed to collect samples from intercepted emission plumes for later analysis is also described.

Acetaldehyde↗
PubMed1998

Soleus H-reflex gain in elderly and young adults: modulation due to body position.

BACKGROUND: The control of posture and balance in the elderly is a primary health concern. Postural instability directly leads to a greater incidence of falling in the elderly population. One important neuromuscular mechanism instrumental in the control of posture and balance is the reflex system. The purpose of this study was to examine the gain of the soleus H-reflex in young and elderly adults in two different body positions: standing and prone. METHODS: Eighteen neurologically healthy volunteers were categorized by age in two groups: young (n = 9, mean age = 23.3 yr) and elderly (n = 9, mean age = 71.7 yr). In each position, the resting H-max/M-max ratio was determined. The gain of the reflex was also assessed by instructing the subject to perform voluntary contractions of 10, 20 and 30% of their maximum voluntary contraction, using real-time EMG biofeedback. Data were sampled on-line using custom designed software (sample rate = 2 kHz). Dependent variables included the average background EMG of the soleus muscle (40 ms window prior to stimulation) and the peak-to-peak amplitude of the elicited soleus H-reflex. To examine the gain of the reflex, the peak-to-peak amplitude of the H-reflex was plotted against the background EMG activity for each contraction intensity. RESULTS: Results indicated the following: young subjects significantly depressed the H-max/M-max ratio when standing (69.3% prone, 55.1% standing), whereas elderly subjects increased the ratio (36.1% prone, 54.5% standing). Also, the young subjects modulated the gain of the reflex from prone to standing (3.30 prone, 3.68 standing), and the elderly subjects demonstrated no gain modulation in the different body positions (2.23 prone, 1.91 standing). In both body positions the young subjects demonstrated significantly higher gain that the elderly subjects. CONCLUSIONS: The results demonstrate different control strategies for young and elderly subjects between prone and standing body positions.

Adult↗