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PubMed1990

Statistical analysis of dose-response curves in extracellular electrophysiological studies of single neurons.

The application of polynomial regression and the analysis of covariance (ANCOVA) to dose-response (DR) data derived from extracellular electrophysiological studies of midbrain dopamine neurons and noradrenergic locus coeruleus neurons in vivo is demonstrated and discussed. Third-order polynomial regression was found to be a better method for estimating ED50 values than probit analysis of linear regression. ANCOVA provides a more powerful statistical method than ANOVA for detecting significant differences in ED50 values or DR curves when a confounding variable such as basal discharge rate is present. The methods of analysis presented herein should be useful in the analysis of other types of neurons in electrophysiological studies.

Action Potentials↗

PubMed1986

Folic acid and chromosome breakage. IV. Variance estimates from longitudinal studies of normal individuals and their implications for sample size and power to detect differences between populations.

The frequency of chromosome aberrations was studied in minimal essential medium (MEM) with and without folic acid (FA) in lymphocytes of 4 normal individuals, each sampled 12 times over a 1-year period. The cells cultured without FA had significantly more breaks and gaps. In both media about 75% of aberrations were classified as gaps. Calculations based on variance estimates suggest that the use of medium without FA could enhance the statistical power to distinguish differences in proportions of chromosome breakage between groups in the same study.

Analysis of Variance↗

PubMed2002

Unified sampling approach for multipoint linkage disequilibrium mapping of qualitative and quantitative traits.

Rapid development in biotechnology has enhanced the opportunity to deal with multipoint gene mapping for complex diseases, and association studies using quantitative traits have recently generated much attention. Unlike the conventional hypothesis-testing approach for fine mapping, we propose a unified multipoint method to localize a gene controlling a quantitative trait. We first calculate the sample size needed to detect linkage and linkage disequilibrium (LD) for a quantitative trait, categorized by decile, under three different modes of inheritance. Our results show that sampling trios of offspring and their parents from either extremely low (EL) or extremely high (EH) probands provides greater statistical power than sampling in the intermediate range. We next propose a unified sampling approach for multipoint LD mapping, where the goal is to estimate the map position (tau) of a trait locus and to calculate a confidence interval along with its sampling uncertainty. Our method builds upon a model for an expected preferential transmission statistic at an arbitrary locus conditional on the sampling scheme, such as sampling from EL and EH probands. This approach is valid regardless of the underlying genetic model. The one major assumption for this model is that no more than one quantitative trait locus (QTL) is linked to the region being mapped. Finally we illustrate the proposed method using family data on total serum IgE levels collected in multiplex asthmatic families from Barbados. An unobserved QTL appears to be located at tau; = 41.93 cM with 95% confidence interval of (40.84, 43.02) through the 20-cM region framed by markers D12S1052 and D12S1064 on chromosome 12. The test statistic shows strong evidence of linkage and LD (chi-square statistic = 18.39 with 2 df, P-value = 0.0001).

Asthma↗

PubMed1991

Data analysis and sample size issues in evaluations of community-based health promotion and disease prevention programs: a mixed-model analysis of variance approach.

The growing interest in community-based approaches to health promotion and disease prevention (HP/DP) has been accompanied by a growing need to evaluate the effectiveness of such programs. Special issues that arise in these evaluation studies include (1) entire communities are assigned to intervention and control groups, (2) only a small number of communities can usually be studied, (3) the time course of changes in behavior and other outcomes is often of interest, and (4) surveys to measure such changes over time can be conducted with either repeated cross-sectional samples or with longitudinal samples. This paper shows how these issues can be addressed under a mixed-model analysis of variance approach. This approach serves to unify several ideas in the literature on evaluation of community studies, including use of time-series regression and the question of whether the individual or the community should be the unit of analysis. We also describe how the method can be used to estimate sample size requirements, statistical power, or minimum detectable program effect.

Analysis of Variance↗

PubMed1997

The public release of hospital and physician mortality data in Pennsylvania. A case study.

OBJECTIVES: Using the public reports of the Pennsylvania Health Care Cost Containment Council on coronary artery bypass graft surgery for 1990 to 1992 as a case study, the authors assess the sensitivity of results to the choice of data and statistical methodology. METHODS: Using the Council's public-release data, surgical mortality and utilization were reanalyzed by standard linear models, empirical Bayes methods, Monte Carlo simulations, and hierarchical statistical models. RESULTS: Statistical power calculations demonstrate that the annual volume of bypass surgery for many hospitals and for most surgeons is too small for meaningful mortality comparisons. The number of hospitals and physicians designated as mortality "outliers" in the Council's reports results in part from a failure to adjust critical P values for multiple comparisons. Hierarchical statistical models implemented by mixed effects logistic regression, by contrast, can detect true differences in performance without producing false outliers. Mortality analyses are sensitive to the choice of comorbidities used for severity adjustment of a mortality model. Small-area analyses indicate large differences in the rates of bypass surgery across Pennsylvania, with lower population-based rates of surgery associated with higher population-based inpatient mortality. CONCLUSIONS: Analyses of mortality by operative procedure, rather than by patient diagnosis, should consider the potential for selection bias caused by the decision to elect surgery. The clinical and statistical issues of operative mortality are sufficiently complex to merit review by independent experts before public release of hospital and physician performance measures.

Cardiology Service, Hospital↗

PubMed2001

Detecting differential rater functioning over time (DRIFT) using a Rasch multi-faceted rating scale model.

This paper describes a class of rater effects that depict rater-by-time interactions. We refer to this class of rater effects as DRIFT differential rater functioning over time. This article describes several types of DRIFT (primacy/recency, differential centrality/extremism, and practice/fatigue) and Rasch measurement procedures designed to identify these types of DRIFT in rating data. These procedures are applied to simulated data and are shown to be useful in classifying raters as being aberrant or non-aberrant for primacy, recency, and differential centrality and extremism, particularly for moderate or larger effect sizes. Rates of correct classification for practice and fatigue were lower and statistical power exceeded.50 only with very large effect sizes. Type I error rates (i.e., incorrect nomination) were near expected levels in all cases.

Decision Theory↗

PubMed2005

[The LISA trial-a- randomized, double-blind, placebo-controlled four-arm study of 1,000 patients with nodular goiter in Germany. Study Design and first results of feasibility].

BACKGROUND: Although levothyroxine is the mostly prescribed medicament in Germany, its therapeutic effectiveness in nodular goiter was never studied in a randomized, double-blind trial with sufficient power. Thus, in May 2004 a TSH-adapted (TSH: thyroid-stimulating hormone), randomized, doubleblind, placebo-controlled four-arm (placebo [P] vs. levothyroxine [T] vs. iodine [I] vs. levothyroxine + iodine [TI]) multicenter study was started in Germany (LISA study). PATIENTS AND METHODS: Based on former retrospective and prospective studies, it was calculated that a sufficient statistical power (> 80%) would be achieved with 250 patients in each arm. The primary endpoint of the trial is the 1-year change of ultrasonographically measured total volume of all nodules. Secondary criteria are volume of goiter, number of nodules, and echogenic structure of nodules. While the study is kept strictly double-blind, the dose of levothyroxine in the T and TI groups is adapted once according to 3-month TSH measurements (target range 0.2-0.8 mU/l). RESULTS: Up to now (1 year after beginning), 305 patients have been included. TSH adaptation could be performed without compromising the double-blind character of the study with good results: about 90% of the patients reached the TSH target range. CONCLUSION: Unblinded results are to be expected in 2007.

Adolescent↗

PubMed2006

Variability of bronchial inflammation in chronic obstructive pulmonary disease: implications for study design.

There is variability in the distribution of inflammatory cells in bronchial tissue in chronic obstructive pulmonary disease (COPD). Better strategies for biopsy sampling of the airway mucosa may improve the capacity to show a difference between study populations where variability in distribution exists. The current authors have examined sources of biological variability in the quantification of inflammatory cells in endobronchial biopsies using immunostained samples taken from 51 subjects with COPD, with a mean forced expiratory volume in one second of 1.71 L, 55% predicted. The distribution of variance contributed by different sources was similar for different inflammatory cell types. For CD8+ cells, a key inflammatory cell in COPD, the largest contribution to intra-subject variability (39%) was time (i.e. 10 weeks between biopsies of placebo-treated subjects), followed by airway generation (23%), biopsy (2.5%), zone (within section; 1.4%) and section (0.4%). Power calculations demonstrated that examining one section from one biopsy, from each of two airway generations, would require a sample size of 32 subjects per group to show a difference of one doubling or halving in CD8+ cells, compared with 47 subjects per group if only one airway generation was sampled. Therefore, biopsies from more than one airway generation should be examined in order to maximise statistical power to detect a difference between study groups.

Adult↗

PubMed2005

Stressful life events and onset of mood disorders in children of bipolar parents during 14-month follow-up.

BACKGROUND: Although multiple studies have examined the association between stressful life events (SLEs) and the development of mood disorders, the exact nature of the association and the degree to which it is independent from familial loading (FL) and gender-specific are still not fully elucidated. AIMS: To study the association between person-independent and -dependent SLEs and first onset or recurrence of a DSM-IV mood disorder episode (MDE) in offspring of bipolar parents. To examine interaction effects of SLEs with familial loading and gender. METHOD: Offspring of bipolar parents (N=132) were assessed with the K-LEDS, the FHRDC and the K-SADS. Logistic regression analysis was used to examine main and interaction effects of various operationalizations of SLEs, familial loading and gender. RESULTS: Dependent SLEs were more likely to occur before onset among the 13 offspring who had a MDE onset during the 14-month follow-up (39%) than in a comparable period among the 67 controls without any lifetime diagnosis (10%). Associations were slightly stronger for first onsets than for recurrences. The association between SLEs and MDE onset/recurrence was independent of socio-demographic characteristics and familial loading, but disappeared when adjusted for baseline anxious/depressive symptoms. Gender and familial loading did not modify the influence of any SLE measure on the development of mood disorders. CONCLUSIONS: In this sample of bipolar offspring dependent stressful SLEs triggered the onset of MDEs, but this association disappeared after adjustment of prior anxious/depressive symptoms, indicating that the association between SLEs and MDE is probably a spurious association. No interaction was found between SLE and FL and gender. Prior anxious/depressive symptoms seem to increase the risk for both occurrence of dependent SLEs and MDE onset or recurrence. LIMITATIONS: Limited statistical power due to small number of MDE onsets.

Adolescent↗

PubMed2002

Comparisons of the variability of three markers of the human circadian pacemaker.

A circadian pacemaker within the central nervous system regulates the approximately 24-h physiologic rhythms in sleep cycles, hormone secretion, and other physiologic functions. Because the pacemaker cannot be examined directly in humans, markers of pacemaker function must be used to study the pacemaker and its response to environmental stimuli. Core body temperature (CBT), plasma cortisol, and plasma melatonin are three marker variables frequently used to estimate the phase of the human pacemaker. Measurements of circadian phase using markers can contain variability due to the circadian pacemaker itself, the intrinsic variability of the marker relative to the pacemaker, the method of analysis of the marker, and the marker assay. For this report, we compared the mathematical variability of a number of methods of identifying circadian phase from CBT, plasma cortisol, and plasma melatonin data collected in a protocol in which pacemaker variability was minimized using low light levels and regular timing of both the light pattern and the rest/activity schedule. We hoped to assess the relative variabilities of the different physiological markers and the analysis methods. Methods were based on the crossing of an absolute threshold, on the crossing of a relative threshold, or on fitting a curve to all data points. All methods of calculating circadian phase from plasma melatonin data were less variable than those calculated using CBT or cortisol data. The standard deviation for the phase estimates using CBT data was 0.78 h, using cortisol data was 0.65 h, and for the eight analysis methods using melatonin data was 0.23 to 0.35 h. While the variability for these markers might be different for other subject populations and/or less stringent study conditions, assessment of the intrinsic variability of the different calculations of circadian phase can be applied to allow inference of the statistical significance of phase and phase shift calculations, as well as estimation of sample size or statistical power for the number of subjects within an experimental protocol.

Adolescent↗

PubMed2005

Design and analysis of clinical trials with clustering effects due to treatment.

Where patients receive therapy as a group, there are good theoretical reasons to believe that variation in the outcome will be smaller for patients treated in the same group than for patients treated in different groups. Similarly, where different therapists treat different groups of patients, outcome for patients treated by the same therapist may differ less than outcome for patients treated by different therapists. Clinical trials evaluating such therapies need to consider this potential lack of independence. As with cluster-randomized trials, this has implications for the precision of treatment effects estimates and statistical power. There are nevertheless differences between clustering due to the organization of treatment and that due to randomization. In cluster-randomized trials the distribution of cluster sizes in each treatment arm should be similar as a consequence of randomization unless there is differential loss to follow-up. With clustering due to therapy group or therapist, cluster size may differ systematically between treatment arms, due to size of therapy groups or differing health professional caseload. Intra-cluster correlation may also differ between treatment arms. The implications of differential cluster size and intracluster correlation for design and analysis will be illustrated by data from two trials, the first comparing nurse practitioner care with general practitioner care, and the second comparing a group therapy with individual treatment as usual. The special case where a group therapy or therapist is compared with an unclustered treatment is examined in detail using a simulation study. The implications of differential clustering effects for sample size and power are addressed. It is argued that the design and analysis of this type of trial should take account of possible heterogeneity in cluster size and intracluster correlation.

Cluster Analysis↗

PubMed2000

Coronally advanced flap for the treatment of buccal gingival recessions with and without enamel matrix derivative. A split-mouth study.

BACKGROUND: The coronally advanced flap (CAF) is a predictable method for achieving root coverage in buccal gingival recessions. The use of enamel matrix derivative (EMD) has already been tested in treating intrabony defects. No clinical comparative study has been published evaluating the CAF in combination with EMD in treating buccal gingival recessions. METHODS: This split-mouth study was performed to assess the efficacy of EMD to improve the results of a root coverage procedure. Fourteen pairs of Miller Class I and II bilateral comparable defects were selected in 12 patients. In each patient, one site was randomly assigned to the test group and the contralateral site to the control group. The treatment consisted of a CAF procedure with (test) or without (control) EMD. Gingival recession (REC), clinical attachment level (CAL), probing depth (PD), and extension of keratinized tissue (KT) were recorded at baseline and 6 months postsurgery. RESULTS: The average initial REC was 3.71 mm (SD +/- 1.68) for the test group, and 3.50 mm (SD +/- 1.56) for the control group. The 2 groups were statistically homogeneous. The mean root coverage was 3.36 mm (SD +/- 1.55), corresponding to a value of 91.2% for the test group, and 2.71 mm (SD +/- 1.20), equal to 80.9% for the control group. The differences between the 2 groups were not statistically significant. The mean CAL gain was 3.57 mm (SD +/- 1.55) for the test group and 2.79 mm (SD +/- 1.19) for the control group. No changes of PD and KT were found. CONCLUSIONS: This study suggests that EMD does not seem to significantly improve the clinical outcomes of gingival recession treated by means of CAF, even though the test group showed slightly better results in terms of root coverage and CAL. Further studies with a larger number of teeth and higher statistical power are needed to support this conclusion.

Adult↗

PubMed1988

An N of 1 service: applying the scientific method in clinical practice.

The N of 1 service at our institution acts as a full referral service for clinicians who want a definitive answer to a difficult management question, and an instructional environment for clinicians who have more time and want to learn to run their own N of 1 RCT. The trial design is a double blind, randomized pair, multiple crossover. A number of methodologic issues are discussed, such as appropriateness of the patients problem to N of 1 trials, feasibility, types of measurement, such as clinical objective measurement and quality of life measurement, as well as timing of these measurements. The analysis issues include developing a reporting method which is statistically powerful and understandable to clinicians with little research background. Some of these issues have been well investigated and some have not.

Clinical Trials as Topic↗

PubMed2001

Alcohol consumption and mortality rates from traffic accidents, accidental falls, and other accidents in 14 European countries.

AIMS: To evaluate the effects of changes in aggregate alcohol consumption on fatal motor vehicle traffic accidents, accidental falls, and other accidents in 14 western European countries after 1950, and to compare traditional beer, wine and spirits countries. DESIGN, SETTING AND PARTICIPANTS: The countries were sorted into three groups. Gender-specific, age-adjusted annual mortality rates (15-69 years) were analysed in relation to per capita alcohol consumption, utilizing the Box-Jenkins technique for time series analysis. All series were different to remove long-term trends. The results of the analyses of individual countries were pooled within each group of countries to increase the statistical power. MEASUREMENTS: Overall accident mortality data for 5-year age groups were converted to age-adjusted mortality rates for the age group 15-69 years, using a European standard population. Data on per capita alcohol consumption were converted to consumption per inhabitant 15 years and older. FINDINGS: For male accidental falls, the analyses uncovered a statistically significant association with alcohol consumption in northern and central Europe, but not in southern Europe. Among females the association was insignificant in all regions. For male traffic accidents, significant relationships were uncovered in central and southern Europe, but not in northern Europe. Among females the effect was significant only in central Europe. For the remaining fatal accidents a significant relationship was found for north European males only. CONCLUSION: The association between aggregate alcohol consumption and rates of fatal accidents is mainly due to traffic accidents in central and southern Europe, and to falls and other accidents in northern Europe.

Accidental Falls↗

PubMed2006

Population-based sample reveals gene-gender interactions in blood pressure in White Americans.

The influence of genetic contributors, such as common single nucleotide polymorphisms, on blood pressure and essential hypertension may vary with the gender. We used the power of a large, community-based sample to probe whether gender interacts with genes in contributing to extremes of blood pressure in 611 male and 656 female age-matched white Americans within the top and bottom 5th percentiles of blood pressure among >53 000 people in a health maintenance program. This approach has >90% statistical power to detect genes contributing as little as 3% to trait (blood pressure) variation. We scored approximately 60 000 genotypes in the subjects: 48 single nucleotide polymorphisms at 33 autosomal and 2 X-linked genes in adrenergic and renal pathways that regulate blood pressure. Six individual variants significantly affected blood pressure and demonstrated gene-by-gender interaction, yielding different effects of the single nucleotide polymorphism on blood pressure in males and females. In females, polymorphisms at beta(1)-adrenergic receptor and alpha(2A)-adrenergic receptor contributed to blood pressure, whereas in men, polymorphisms at beta(2)-adrenergic receptor and angiotensinogen were associated. An alpha(2A)-adrenergic receptor haplotype influenced blood pressure in women, whereas 2 angiotensinogen haplotypes were associated in men. We also detected gene-by-gene, gender-specific interactions (epistasis) in pathophysiological pathways. This study reveals gender-specific effects of single nucleotide polymorphisms, haplotypes, and gene-by-gene interactions that determine blood pressure in white Americans. Such genetic variants may define genetically and etiologically distinct subgroups of men and women with essential hypertension and may have implications for rational treatment selection.

Adult↗

PubMed1995

A mini-lesson in statistics: what causes treatment groups to be deemed 'not statistically different'?

The theory behind a "not-statistically significant difference" (NS) in group comparison research is crucial for proper study design. Proprietary company-sponsored research whose purpose is to demonstrate null intervention effects is widespread. Therefore, a discussion of null effects in research results was undertaken. Type I and Type II errors are explained, and reasons for "NS" results detailed. Clinical differences, power, statistical tests chosen, and values of alpha and beta are included in the discussion. Examples from studies of the effects of artificial baby milk gift packs are offered. If the aim of research is to demonstrate NS between treatments, or if the conclusion of published research is NS, then the research must demonstrate a design which ensures ethical and appropriate levels of both Type I and Type II errors.

Bias↗

PubMed2000

Investigation of the human hippocampal formation using a randomized event-related paradigm and Z-shimmed functional MRI.

Functional neuroimaging of the hippocampal formation has presented a challenge to neuroscientists because of the small size of the hippocampus proper and its location at the basal level of the brain. Choosing the appropriate control condition for subtraction-based studies has also proved difficult. Event-related experimental designs are a powerful tool in behavioral and electrophysiological studies. Recently, such experimental designs have been applied to functional MR imaging studies but these studies used large intertrial intervals in order to separate the slow blood flow response from temporally adjacent events, severely limiting the number of events that can be presented in a single run. This leads to poor statistical power and restrictions on the design of the experimental paradigm. We present data obtained using a rapidly presented, randomized event-related paradigm, combined with a novel fMRI imaging method designed to improve imaging in basal brain regions. The results demonstrate bilateral activation in the hippocampal formation in identification of novel complex scenes distinct from a learned basis set of complex scenes. Differential activation is obtained in the counter task of identifying a learned target complex scene against a background of novel scenes. The results are also compared with the more conventional block design complex scene paradigms previously reported by others. The block design provides strong posterior activation, likely related more to visual scene processing, whereas the event-related design provides more anterior hippocampal activation with the encoding of novel scenes.

Adult↗

PubMed2002

Combining brains: a survey of methods for statistical pooling of information.

More than one subject is scanned in a typical functional brain imaging experiment. How can the scientist make best use of the acquired data to map the specific areas of the brain that become active during the performance of different tasks? It is clear that we can gain both scientific and statistical power by pooling the images from multiple subjects; furthermore, for the comparison of groups of subjects (clinical patients vs healthy controls, children of different ages, left-handed people vs right-handed people, as just some examples), it is essential to have a "group map" to represent each population and to form the basis of a statistical test. While the importance of combining images for these purposes has been recognized, there has not been an organized attempt on the part of neuroscientists to understand the different statistical approaches to this problem, which have various strengths and weaknesses. In this paper we review some popular methods for combining information, and demonstrate the surveyed techniques on a sample data set. Given a combination of brain images, the researcher needs to interpret the result and decide on areas of activation; the question of thresholding is critical here and is also explored.

Adult↗