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PubMed2006

The importance of analyzing graft and patient survival by cause of failure: an example using pediatric small intestine transplant data.

BACKGROUND: Although graft and patient survival are vital in reporting overall results of clinical transplant studies, these outcomes do not account for distinct types of graft failure and death, which clearly exist in pediatric small intestine transplantation (Itx). The use of a cause-specific hazard (CSH) approach may provide more precise identification and thus greater insight as to why certain factors are prognostically important. METHODS: Among 119 pediatric patients who received primary Itx at our center since 1994, Cox model stepwise regression analyses were performed to identify prognostic factors for the following CSH rates: intestinal graft failure (IGF)/death due to rejection, death due to infection not triggered by IGF, and intestinal graft loss/death due to other causes. RESULTS: Two factors were associated with a significantly higher rate of developing IGF due to rejection (23 such failures): receiving an isolated intestine or liver-intestine transplant (P=0.00001) and receiving no induction agent (P=0.006). Conversely, age at transplant <1 year was the single factor associated with a significantly higher death rate due to infection (P=0.0005) (21 such deaths). Two characteristics were associated with a significantly higher death rate due to other causes: being in the hospital pretransplant (P=0.007) and not receiving daclizumab induction therapy (P=0.02) (24 such deaths). Although these four factors (transplant type/age/hospital status/induction therapy) were, for the most part, associated with graft/patient survival, the CSH analysis more precisely identified their prognostic value and achieved greater statistical power. CONCLUSIONS: A CSH approach should be used in conjunction with overall outcome analyses.

Cohort Studies↗
PubMed2005

Research reports on treatments for bipolar disorder: preliminary assessment of methodological quality.

OBJECTIVE: To assess frequencies of types of publications about bipolar disorder (BD) and evaluate methodological quality of treatment studies. METHOD: We classified 100 randomly selected articles (1998-2002) from five psychiatric journals with highest impact ratings, by topic areas, and assessed methods employed in treatment studies. RESULTS: Topics ranked: treatment (41%; 37% on pharmacotherapy) > biology (31%) > psychopathology (14%) = miscellaneous (14%). Of treatment studies, only 19% of original articles were randomized, 15% were relatively large (n > or = 50) but non-randomized, 65% were small non-randomized, case-series or -reports, and 53% relied on baseline-to-endpoint contrasts without a control group. Patient dropout rates were > or =40% in 43% of prospective studies. Only two reports provided confidence intervals; one included a power analysis, and 53% included no references on study design or statistical methods. CONCLUSION: Even in highly respected journals, the typical methodological quality of recent reports on therapeutics for BD was unexpectedly limited, and psychopathology and psychotherapies were little studied.

Bipolar Disorder↗
PubMed1984

Relative effectiveness of a rotary and conventional toothbrush in plaque removal.

The ability of a powered rotary toothbrush to remove 3- and 4-day-old microbial plaque deposits was evaluated in 10 young adults with healthy gingivae. Using a split mouth technique and a cross-over experimental design, the powered brush was compared with a conventional hand brush over a 14-day period. Statistical analysis of the results showed no significant differences between either method of brushing when the whole mouth, maxillary or mandibular arches were compared. Further analysis of the proximal scores again showed no significant differences between the powered brush or handbrush. The majority of the subjects preferred the conventional handbrush to the powered brush.

Adult↗
PubMed2005

Isolation by distance, web service.

BACKGROUND: The population genetic pattern known as "isolation by distance" results from spatially limited gene flow and is a commonly observed phenomenon in natural populations. However, few software programs exist for estimating the degree of isolation by distance among populations, and they tend not to be user-friendly. RESULTS: We have created Isolation by Distance Web Service (IBDWS) a user-friendly web interface for determining patterns of isolation by distance. Using this site, population geneticists can perform a variety of powerful statistical tests including Mantel tests, Reduced Major Axis (RMA) regression analysis, as well as calculate FST between all pairs of populations and perform basic summary statistics (e.g., heterozygosity). All statistical results, including publication-quality scatter plots in Postscript format, are returned rapidly to the user and can be easily downloaded. CONCLUSION: IBDWS population genetics analysis software is hosted at http://phage.sdsu.edu/~jensen/ and documentation is available at http://www.bio.sdsu.edu/pub/andy/IBD.html. The source code has been made available on Source Forge at http://sourceforge.net/projects/ibdws/.

Computer Graphics↗
PubMed2005

A randomised controlled trial to assess the effectiveness of offering study results as an incentive to increase response rates to postal questionnaires [ISRCTN26118436].

BACKGROUND: Postal questionnaires are widely used to collect outcome data on participants. However, a poor response to questionnaires will reduce the statistical power of the study and may introduce bias. A meta analysis of ten trials offering study results, largely in the fields of education and marketing, was shown to be ineffective, with the odds ratio for response with offering research findings is 0.92 (95% CI 0.75 to 1.11). However uncertainty still exists as it is uncertain whether results from such trials can be extrapolated to that of a health care setting. The aim of this study was to assess whether offering participants study results increases the response rates to postal questionnaires. METHODS: 1038 women aged over 70 years were remotely randomised by computer in a 3:1 ratio. 250 participants did not receive the offer of knowing the results of the trial and 788 participants were offered the results of the trial in a postal questionnaire. The main outcome measure was response rate. Chi square test was used to evaluate the overall differences in response rate between the two groups. An adjusted analysis, adjusting for whether the participant was taking calcium and age was also undertaken. RESULTS: The response rates were not significantly different Odds Ratio 0.88 (95% confidence intervals 0.48 to 1.63) p = 0.69. CONCLUSION: Offering study results to women living in the community aged over 70 does not increase response rates to postal questionnaires. Although researchers have an ethical obligation to offer participants study results, since 10% of women did not wish to receive the results, investigators should give participants the option to opt out of receiving the study's results.

Aged↗
PubMed2006

[Comparison of influential variables for smoking temptation between adolescent and adult smokers].

PURPOSE: This study attempted to identify influential variables on smoking temptation between groups: adolescent smokers and adult smokers. METHOD: A survey was conducted with 376 adolescent smokers in 4 high schools and 451 adult smokers in community settings in South Korea. Univariate statistics and regression were used for data analysis. RESULT: The most powerful predictor of smoking temptation for adolescent smokers was nicotine dependency. On the other hand, the most powerful predictor of smoking temptation for adult smokers was self-efficacy for smoking abstinence. In the high smoking temptation group, depression and nicotine dependency were the predictors for smoking temptation for adolescent smokers and nicotine dependency and pros for smoking were the predictors for smoking temptation for adult smokers. In the low smoking temptation group, cons for smoking and process of change for smoking abstinence were the predictors on smoking temptation for adolescent smokers and self-efficacy for smoking abstention and pros for smoking were the predictors on smoking temptation for adult smokers. CONCLUSION: There were different influential variables on smoking temptation according to age groups and level of smoking temptation. Smoking-cessation interventions should be tailored to the level of smoking temptation of the individual smokers.

Adolescent↗
PubMed1999

[Methodological aspects of biostatistics and epidemiology in a clinical trial].

Various methodological issues in biostatistics and epidemiology which are relevant for the development of a clinical trial are discussed. A brief set of definitions regarding clinical trials and methods for the assignment of treatments is presented. In addition, methods to reduce the possibility of bias that may be introduced into a clinical trial are summarized. The different elements that must be included in the informed consent form are defined. General considerations for data analysis and for sample size required to obtain an adequate statistical power are illustrated. Finally, critical questions that can be used for the review of the literature on clinical trials are suggested.

Aged↗
PubMed2000

HLA-DQB1 genotyping with simple automated DNA sequencing and single-strand conformation polymorphism analysis.

BACKGROUND AND PURPOSE: Accurate human leukocyte antigen (HLA) typing is important for matching donors and recipients of bone marrow transplantation. Because HLA is highly polymorphic, HLA genotyping is also a valuable tool in forensic identification of humans. The primary objective of this study was to establish a simple, rapid, and economic HLA analysis system suitable for use in forensic applications. METHOD: We used the primer pair DB130 and CH29 to amplify the HLA class II DQB1 gene by polymerase chain reaction (PCR). The nucleotide sequences of the PCR products were analyzed with an ABI Prism 377 automatic DNA sequencer, with the aid of its systematic analytical procedure. Some genotypes were confirmed by single-strand conformation polymorphism (SSCP) analysis. RESULTS: We identified 15 alleles and 37 genotypes from 86 Taiwanese subjects. The most frequent allele was 03011 (27.9%) and the most frequent genotype was 03011/03011 (15.1%). Statistical analysis showed that the allelic diversity was 0.862 and the power of discrimination was 0.948. CONCLUSIONS: The results of this study indicate that the combined use of automated sequencing with only one primer pair and SSCP provides a simple, rapid, and economic tool for analyzing the DQB1 gene. Compared with other sequencing methods that use a set of multiple primers, this method has two advantages. First, it is simpler and faster, because the HLAB1 genotype can be determined in a single PCR reaction. Second, the use of only one primer set obviates the need for preferential annealing of any one primer set.

Forensic Medicine↗
PubMed1994

[Keratoconus and familial topographic corneal anomalies].

PURPOSE: Computer-assisted corneal topography, allows the detection of early abnormalities, including abortive or subclinical forms of keratoconus. So, it is possible to identify affected individuals with variable degrees, in family members of patients with keratoconus, to draw pedigrees, and to specify the mode of inheritance. METHODS: Computer-assisted digital videophotokeratoscope was used to map the corneas of 106 family members of 30 patients with keratoconus. RESULTS: Abnormalities observed included the inferior cornea markedly steeper than the superior cornea (I-S - 0.86 +/- 0.44 D) and a marked difference between the central corneal powers of the two eyes (delta PC = 0.72 +/- 0.22 D). However, there was no statistical difference with normal individuals for central corneal power. CONCLUSION: Pedigree analysis in these families suggests, in 50% of them, an autosomal dominant mode of inheritance. However, it is impossible to conclude for the other families, because of an insufficient number of cases.

Adult↗
PubMed1995

[The objective and perspective of recording electrical activity from the central nervous system].

In 1929 Hans Bergr successfully recorded electrical activity from the human brain using surface scalp electrodes. Since, the EEG has brought significant contributions to the fields of clinical neurology and neurophysiology. As a clinical diagnostic tool, the EEG has provided information for functional as well anatomical (structural) brain disturbances. As a functional diagnosis, the EEG is far superior to other functional tests such as PET, SPECT or functional MRI because of its excellent temporal resolution representing moment to moment changes in the level of consciousness. However, the progress has been hampered due to difficulty in quantifying EEG data because of its extreme dynamics and variability, which perhaps reflects yet unknown brain functions. This difficulty will be overcome by improved quantification methods and statistical measures using various computer applications including topographic mapping, power spectrum analysis, covariance, correlation or coherence function. Because of its poor spacial resolution, the EEG has relinquished its place to CT and MRI scans as an anatomical diagnostic tool. The surface recorded electrical activity is greatly attenuated and distorted by the time it reaches to the scalp. This is due to the inhomogeneous tissues (CSF, dura, skull, scalp) that intervene between the recording electrodes and cortical surface. Because the human body or head consists of electroconductive media of various geometries, current distortion, far-field potentials or paradoxical lateralizations further complicate the interpretation of EEG in postulating the location of anatomical generator sources from surface recorded EEG. Advanced computer technology is in progress to quantify the EEG data by taking into account the factors of conductivity, geometry shape and individual head size. This will improve the accuracy of localizing current generator sources in relationship to brain anatomy. By solving these problems in a methodical fashion, EEG will become the revelation for understanding the functional anatomy of brain and will step closer to Berger's dream, "EEG is a window of human mental activity".

Action Potentials↗
PubMed2004

Survival analysis of dropout patterns in dieting clinical trials.

Subjects who withdraw from diet clinical trials are a drain on limited resources and reduce statistical power. Dropout pattern data, collected during a clinical trial for which the primary findings compared weight loss from three dieting protocols, are examined using survival analysis and found to be exponentially distributed. The predicted probability of remaining in the study is 83% for 30 days and 60% for 84 days. Survival analysis methods consider subjects who did not return after the initial visit and others who may have continued dieting beyond study termination. When applied to clinical trials, this type of analysis provides valuable information for planning and budgeting of future trials. Inclusion of a 1- to 2-week run-in period at the beginning of the study may improve retention. Otherwise, the diet researcher should consider increasing initial randomized sample size by approximately 10% to 25% as an allowance for early withdrawals.

Body Mass Index↗
PubMed1987

The positive approach to negative results in toxicology studies.

Negative results in toxicology studies are often as noteworthy as are results that detect significant toxicological effects. The results of 49.1% of all t tests published in Ecotoxicology and Environmental Safety in 1985 and 1986 were negative. However, despite the importance and prevalence of negative results in toxicology studies, they are frequently misinterpreted. Negative results from statistical tests that have poor statistical power can only be considered to be inconclusive. Because toxicology studies often use small sample sizes, such studies often have poor power to detect small, but biologically significant, effects. Toxicologists may improve the power of their tests by improving experiment design, increasing alpha, increasing sample size, or limiting the analysis to detection of large differences among samples. Selection of both sample size and alpha level should take considerations of statistical power into account.

Research↗
PubMed1985

Uses and abuses of analysis of covariance in clinical trials.

Measurement of improvement in clinical trials in chronic diseases commonly compares baseline data to endpoint values by performing t-tests or analysis of variance (ANOVA) on raw gains or percentage changes. This procedure can be misleading and the use of an analysis of covariance (ANCOVA) should be considered. Properly used, ANCOVA increases statistical power in a clinical trial. However, its advantage over t-tests can be nullified by small numbers of patients, violations of assumptions, and incorrect application of the techniques. An evaluation of ANCOVA in chronic disease studies is given, with examples of its strengths and weaknesses as seen in several drug trials in the rheumatic diseases. Recommendations on its use and a decision tree for the nonstatistician are provided.

Analysis of Variance↗
PubMed2002

Ambulatory monitoring of blood pressure in growth hormone-deficient adults.

The aim of this study was to evaluate the 24-h pattern of blood pressure in adults with growth hormone deficiency using ambulatory blood pressure monitoring. We therefore evaluated the mean systolic and diastolic blood pressures, systolic and diastolic blood pressure loads and diurnal blood pressure rhythm. We used an auscultatory-type monitor, the measurements being made at 10-15 min intervals during the day and 20-30 min intervals at night. We included patients with a growth hormone peak of less than 3 ng/ml in at least two stimulation tests: the insulin tolerance and glucagon tests. The exclusion criteria were mental illnesses, pregnancy, diabetes mellitus, blood pressure higher than 160/90 mmHg, the use of growth hormone in the previous 12 months, severe acute illnesses, chronic liver or kidney disease and a history of malignancy. The results were interpreted according to the II Brazilian Consensus for the utilization of ambulatory monitoring. The study population comprised 27 adult patients with growth hormone deficiency, 11 male and 16 female, with an age range of 21-62 years. Five had developed the condition during childhood, whereas the remainder had adult-onset growth hormone deficiency. The mean systolic (115 +/- 16.7 mmHg) and diastolic blood pressure loads (75.51 +/- 1.90 mmHg) were normal. There was a tendency towards a lower blood pressure in patients with childhood-onset growth hormone deficiency when compared with their adult-onset counterparts. Men had a lower systolic blood pressure than women, the same pattern being found for mean diastolic blood pressure. Multiple regression analysis showed that age was the only independent variable with the statistical power to explain the variance of blood pressure in this group of patients. The incidence of non-dippers was 37.03%. Growth hormone deficiency thus seems to be associated with a change in the 24-h blood pressure pattern, with a high incidence of non-dippers.

Adult↗
PubMed2006

An assessment of recently published gene expression data analyses: reporting experimental design and statistical factors.

BACKGROUND: The analysis of large-scale gene expression data is a fundamental approach to functional genomics and the identification of potential drug targets. Results derived from such studies cannot be trusted unless they are adequately designed and reported. The purpose of this study is to assess current practices on the reporting of experimental design and statistical analyses in gene expression-based studies. METHODS: We reviewed hundreds of MEDLINE-indexed papers involving gene expression data analysis, which were published between 2003 and 2005. These papers were examined on the basis of their reporting of several factors, such as sample size, statistical power and software availability. RESULTS: Among the examined papers, we concentrated on 293 papers consisting of applications and new methodologies. These papers did not report approaches to sample size and statistical power estimation. Explicit statements on data transformation and descriptions of the normalisation techniques applied prior to data analyses (e.g. classification) were not reported in 57 (37.5%) and 104 (68.4%) of the methodology papers respectively. With regard to papers presenting biomedical-relevant applications, 41(29.1 %) of these papers did not report on data normalisation and 83 (58.9%) did not describe the normalisation technique applied. Clustering-based analysis, the t-test and ANOVA represent the most widely applied techniques in microarray data analysis. But remarkably, only 5 (3.5%) of the application papers included statements or references to assumption about variance homogeneity for the application of the t-test and ANOVA. There is still a need to promote the reporting of software packages applied or their availability. CONCLUSION: Recently-published gene expression data analysis studies may lack key information required for properly assessing their design quality and potential impact. There is a need for more rigorous reporting of important experimental factors such as statistical power and sample size, as well as the correct description and justification of statistical methods applied. This paper highlights the importance of defining a minimum set of information required for reporting on statistical design and analysis of expression data. By improving practices of statistical analysis reporting, the scientific community can facilitate quality assurance and peer-review processes, as well as the reproducibility of results.

Analysis of Variance↗
PubMed2005

Does loading time affect implant survival? A meta-analysis of 1,266 implants.

BACKGROUND: Considerable controversy exists as to whether immediate or early implant loading is associated with a higher failure rate compared to conventional loading. Numerous trials conducted have yielded inconsistent results, partly due to low statistical power. Thus, we sought to determine whether combining results from all published trials would provide a better estimate of the impact of implant loading time on survival. METHODS: We carried out a meta-analysis of all previously published prospective trials comparing conventional with early or immediate implant loading. The outcome of interest was implant failure rate. The Q statistics test was used to assess the presence of heterogeneity. We identified relevant studies through a search of the MEDLINE database and the Cochrane Registry of Controlled Trials. RESULTS: We found 13 prospective trials (1,266 implants) in which early or immediate implant loading was compared to conventional loading. Overall there was no difference in implant failure rate between loading techniques (odds ratio [OR] 0.91; 95% CI: 0.41 to 2.03; P=0.41). Implant failure occurred slightly, although not statistically significant, less often with early implant loading (OR 0.52; 95% CI: 0.22 to 1.24; P=0.07). Immediate implant loading was associated with slightly, although not statistically significant, worse outcomes (OR 1.26; 95% CI: 0.38 to 4.13; P=0.35). Pooling of randomized controlled trials (RCTs) confirmed these results. CONCLUSIONS: In a meta-analysis of 13 prospective trials, early implant loading was not associated with worse outcomes compared to conventional loading. Further evaluations in adequately powered large prospective trials are needed to confirm these findings.

Controlled Clinical Trials as Topic↗
PubMed1990

A comparison of multivariable mathematical methods for predicting survival--III. Accuracy of predictions in generating and challenge sets.

This paper concludes a study of "performance variability" when four methods of multivariable analysis--multiple linear regression, discriminant function analysis, multiple logistic regression, and two arrangements of Cox's proportional hazards regression--were applied to the same stratified random samples of "generating sets" containing seven different statistical distributions of cogent biologic attributes in a composite staging system for a large cohort of patients with lung cancer. Each model developed from the generating sets was also applied for predictions in a previously sequestered "challenge set". Across the different generating sets, the multivariable methods showed good agreement with one another in the stepwise choice of first two powerful predictor variables, but not in the sequence of subsequent choices or in the standardized coefficients assigned to the same collection of "forced" variables. In concordance of predictions for individual patients in the generating sets, the overall proportions of disagreement for pairs of methods ranged from 0 to 28%, and kappa values ranged from 0.49 to 1.00. The accuracy of individual predictions showed relatively similar results when the different methods were applied to the same generating set. Across the generating sets, the different methods showed similar total results but substantial variations in predictions for alive and dead patients. When the models from the generating sets were applied for predictions in the challenge set, the results showed an analogous pattern: similar accuracy within models for overall and live/dead predictions, but substantial variations in live/dead predictions across models derived from different generating sources. The results showed that the multivariable methods often had good agreement with one another in predictions for groups but not for individual persons; and that no single method was superior to the others or to the composite staging system. We conclude that multivariable analytic methods may be most effective and consistent if used to find the few most powerful predictor variables, omitting the many other variables that may be "statistically significant" but less cogent. The powerful predictors may sometimes be best constructed, before the analysis begins, as composite variables containing appropriate unions or ordinal arrangements of elemental candidate variables.

Cohort Studies↗
PubMed2002

The economics of basiliximab (Simulect) in preventing acute rejection in renal transplantation.

An economic evaluation was undertaken alongside a multicentre international trial of basiliximab. Resource usage within the trial was assessed, and the cost implications of using basiliximab evaluated. Recipients of a primary cadaveric kidney transplant were recruited into a double-blind trial and received either placebo ( n=186) or basiliximab ( n=190). Clinical outcomes and resource usage were monitored in the 12 months following transplantation. Local unit costs were obtained, and global analysis was undertaken using health sector purchasing-power parity rates. No statistically significant differences were found in the mean cost of treatment per patient. The mean cost of treatment was US$47,940 for basiliximab patients and US$46,280 for placebo patients, a mean difference of US$1,660 (95% confidence interval (CI): -US$4,150, US$7,360; P=0.58). Basiliximab produces clinical benefit in terms of preventing episodes of acute rejection, whilst the difference in the total resource usage and cost of treatment is not statistically significant.

Analysis of Variance↗