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PubMed2006

MMASS: an optimized array-based method for assessing CpG island methylation.

We describe an optimized microarray method for identifying genome-wide CpG island methylation called microarray-based methylation assessment of single samples (MMASS) which directly compares methylated to unmethylated sequences within a single sample. To improve previous methods we used bioinformatic analysis to predict an optimized combination of methylation-sensitive enzymes that had the highest utility for CpG-island probes and different methods to produce unmethylated representations of test DNA for more sensitive detection of differential methylation by hybridization. Subtraction or methylation-dependent digestion with McrBC was used with optimized (MMASS-v2) or previously described (MMASS-v1, MMASS-sub) methylation-sensitive enzyme combinations and compared with a published McrBC method. Comparison was performed using DNA from the cell line HCT116. We show that the distribution of methylation microarray data is inherently skewed and requires exogenous spiked controls for normalization and that analysis of digestion of methylated and unmethylated control sequences together with linear fit models of replicate data showed superior statistical power for the MMASS-v2 method. Comparison with previous methylation data for HCT116 and validation of CpG islands from PXMP4, SFRP2, DCC, RARB and TSEN2 confirmed the accuracy of MMASS-v2 results. The MMASS-v2 method offers improved sensitivity and statistical power for high-throughput microarray identification of differential methylation.

Cell Line, Tumor↗
PubMed1995

Reliability of single and double probing attachment level measurements.

Clarification of the reliability associated with probing attachment level measurements and with diagnostic rules derived from them is necessary to examine the potential of these measurements as reliable markers of the disease process and as an outcome measure in clinical treatment studies. The purpose of the present study was to describe and compare the longitudinal reliability of single and double probing attachment level measurable by estimating false positive and false negative rates. In 20 systemically healthy adults with untreated advanced adult periodontitis, probing attachment levels and probing depth were measured at 6 sites in all teeth at the start of the study, and every 30 days thereafter for 11 months. Attachment levels were double measured, using acrylic onlays providing reference points and an electronic pressure sensitive probe. Attachment loss from baseline of 2.5 mm or more was used to accept dynamic attachment loss. The statistical methods for the cross-sectional analysis included mean absolute differences between double measurements and cross-correlations. Longitudinal analyses, expressing estimates of diagnostic error rates were made using maximum likelihood methods. 5 measurement protocols were compared. The results showed that the mean absolute difference between replicate measurements was 0.095 mm in bicuspids and 0.107 mm in molars. The mean absolute differences decreased over time from 0. 128 mm in visit 3 to 0.08 mm in visit 7. Correlation coefficients for replicate measurements were higher than 0.98. In general, false positive rates were markedly lower (< or = 0.02) than false negative rates (< or = 0.31). The relative sample size required to obtain comparable statistical power, was minimized in premolars when using the first of 2 measurements or the mean of 2 measurements, and in molars when using the first of 2 measurements. The methodology used in the present study provides guidelines for designing clinical studies which maintain statistical power by balancing off examiner reliability and sample size.

Acrylic Resins↗
PubMed1998

[All mortality by cause of death. The challenge of coronary prevention].

Much debate on the benefits and risks of cholesterol lowering to prevent coronary heart disease has focused on excess non-CHD mortality rates reported in some trials. Because of the wide variation in design of cholesterol-lowering trials and because the non-CHD mortality rate was not a controlled endpoint of statistical power in most published studies, it has been difficult to determine whether any excess mortality was due to certain therapies, to other mechanisms, or to chance. As a result, some investigators have performed retrospective analyses of pooled trial data in order to augment statistical power. Some investigators have hypothesized that the human brain is dependent on a constant supply of cholesterol from the circulation and that cholesterol loss in neuronal membranes, with the possible consequences of behavioral disorders and increased risk of accident and violent death. Indeed Weidner and Griffin suggest that low cholesterol is a marker for poor underlying health; physical illnesses are likely to cause depression and other negative emotional states, which are often accompanied by suppressed appetite and weight loss causing reduction in cholesterol levels. Such mental states may also increase the risk of non-CHD death, for example suicide. Rossouw reviews the evidence concerning non-CHD mortality in cholesterol-lowering trials and reports metaanalyses carried out for all trials combined. The findings indicated a significant (15%) increase in non-CHD mortality in all trials combined. However, this was not related to cholesterol lowering itself, because there was no increased risk in trials with > 10% cholesterol reduction, whereas there was a significant (22%) increase in trials with lesser degrees of cholesterol lowering. The publication of a large secondary prevention trial (4S) employing Simvastatin for cholesterol lowering supports the idea that cholesterol reduction itself does not have adverse effects on non-CHD mortality. The overview of all published trials demonstrates their effectiveness in reducing cholesterol and provides clear evidence of benefits on stroke and total mortality. A 10% reduction in cholesterol yielded about a 20% decrease in CHD mortality, which would be expected to result in about a 6% reduction in total mortality. Endothelium-dependent relaxations are reduced in hyperlipidemia and atherosclerosis. Exogenous L-arginine improves or restores the reduced endothelium-dependent relaxations. Moreover inflammation is associates with the initiation and progression of atherosclerosis. The fact of the matter is the Cardiovascular drugs already in clinical use or in development are able to interfere with certain aspects of endothelial function and may be useful in protecting the vessels and, hence, in preventing the development of cardiovascular disease.

Cause of Death↗
PubMed2003

Variation, replication, and power analysis of Myriophyllum spp. microcosm toxicity data.

Myriophyllum spp. have been proposed as a new standard laboratory aquatic macrophyte test species for the registration of pesticides. The main objectives of this investigation were to determine the power of Myriophyllum sibiricum and Myriophyllum spicatum toxicity data derived from an outdoor microcosm bioassay, to evaluate the variation of 10 different aquatic plant endpoints and to calculate the minimum detectable difference for these endpoints, to determine the replication required to detect ecologically significant changes from control for these endpoints, and to make recommendations for future field studies with Myriophyllum spp. Control data from four different studies that characterized haloacetic acid toxicity with Myriophyllum spp. for durations of three to six weeks during the summer of 1999 with five treatment levels (n = 3), including control, were examined. Endpoint coefficient of variation ranged, on average, from 6 to 28%. Node number and plant length endpoints were consistently the most statistically powerful for both plant species. It was possible to detect approximately 30% change from control in both endpoints with high statistical power (beta = 0.2, alpha = 0.05, n = 3). The range of minimum detectable differences was 40 to 60% for the other endpoints. Replication to detect a > or = 25% change from control would require an n of 2 to 21, depending on the endpoint. Myriophyllum sibiricum had slightly lower coefficients of variation and thus required fewer replicates than M. spicatum to be statistically significantly different from control values. Variation within microcosm studies was not significantly different from that of controlled laboratory studies, implying that most of the variation observed in the field is inherent in the plants. Based on statistical sensitivity, ecological relevance, and toxicological sensitivity, we recommend using plant length and root endpoints as indicators of toxicity under field conditions.

Acetic Acid↗
PubMed1999

Using pooled exposure assessment to improve efficiency in case-control studies.

Assays can be so expensive that interesting hypotheses become impractical to study epidemiologically. One need not, however, perform an assay for everyone providing a biological specimen. We propose pooling equal-volume aliquots from randomly grouped sets of cases and randomly grouped sets of controls, and then assaying the smaller number of pooled samples. If an effect modifier is of concern, the pooling can be done within strata defined by that variable. For covariates assessed on individuals (e.g., questionnaire data), set-based counterparts are calculated by adding the values for the individuals in each set. The pooling set then becomes the unit of statistical analysis. We show that, with appropriate specification of a set-based logistic model, standard software yields a valid estimated exposure odds ratio, provided the multiplicative formulation is correct. Pooling minimizes the depletion of irreplaceable biological specimens and can enable additional exposures to be studied economically. Statistical power suffers very little compared with the usual, individual-based analysis. In settings where high assay costs constrain the number of people an investigator can afford to study, specimen pooling can make it possible to study more people and hence improve the study's statistical power with no increase in cost.

Animals↗
PubMedDate not supplied

Children with disturbances in sensory processing: a pilot study examining the role of the parasympathetic nervous system.

This study was a preliminary investigation of parasympathetic nervous system (PNS) functioning in children with disturbances in sensory processing. The specific aims of this study were to (1) provide preliminary data about group differences in parasympathetic functions, as measured by the vagal tone index, between children with disturbances in sensory processing and those without; (2) determine effect size and power needed for future studies; and (3) to lay the foundation for further examination of the relations of parasympathetic functioning and functional behavior in children with disturbances in sensory processing. Participants were 15 children, nine with disturbances in sensory processing and six typically developing children. Heart period data were continuously collected for a 2-minute baseline and during administration of the 15-minute Sensory Challenge Protocol, a unique laboratory protocol designed to measure sensory reactivity (Miller, Reisman, McIntosh, & Simon, 2001). Groups were compared on vagal tone index, heart period, and heart rate using two-tailed, independent sample t tests. Children with disturbances in sensory processing had significantly lower vagal tone than the typically developing sample (t(13) = 2.4, p = .05). Statistical power analysis indicated that, for future studies, a sample size of 20 in each group would yield adequate statistical power. Although the number of subjects in this pilot study is small, the results from this study support further investigations of parasympathetic functions and functional behavior in children with disturbances in sensory processing.

Case-Control Studies↗
PubMed2001

Negative results of randomized clinical trials published in the surgical literature: equivalency or error?

HYPOTHESIS: We hypothesized that review of randomized controlled clinical trials (RCTs) with nonstatistically significant or "negative" results published in the surgical literature do not have appropriate statistical power to demonstrate equivalency between treatment arms. DATA SOURCES AND STUDY SELECTION: The MEDLINE database was searched to obtain reports of all RCTs with negative results published in 3 surgical journals from 1988 to 1998. Manual review of one year (1997) of publications for each journal was performed to validate our search strategy. Equivalency was evaluated using the Two One-Sided Tests Procedure and post hoc power calculations. DATA SYNTHESIS: Ninety reports of RCTs with negative results were identified in the surgical literature between 1988 and 1998. The manual review of 1997 showed a 100% retrieval rate for our search strategy. After applying the Two One-Sided Tests Procedure, 35 reports (39%) met the criteria for demonstrating equivalency. The other 55 reports (61%) contained at least a 10% absolute difference in the 90% confidence interval of Delta. Using the power calculation method, only 22 (24%) articles had a power greater than.80 to detect a 50% difference in therapeutic effect. Only 29% of the reports included a formal sample size calculation and these studies were more likely to demonstrate equivalency than those without a sample size estimate (P<.01). CONCLUSIONS: Many reports from negative RCTs published in the surgical literature lack sufficient statistical power to establish that clinically important differences are not present. Surgeons should perform appropriate sample size calculations when designing RCTs and recognize the utility of confidence intervals when reporting negative results.

Confidence Intervals↗
PubMed1997

The association between hypertensive disorders of pregnancy and abnormal second-trimester maternal serum levels of hCG and alpha-fetoprotein.

OBJECTIVE: To examine the association between hypertensive disorders of pregnancy and second-trimester maternal serum alpha-fetoprotein (MSAFP) and hCG levels. METHODS: The proportions of abnormal second-trimester MSAFP and hCG levels in the serum samples from 65 women with true pregnancy-induced hypertension or preeclampsia (cases) were compared to the proportions of abnormal levels in all 1943 women without this disorder in the same cohort in a hospital setting. Maternal serum alpha-fetoprotein and hCG levels of the 65 cases also were compared to those of 325 completely uncomplicated matched control pregnancies, selected from the same cohort. Fisher exact test and Student t test were used for statistical analysis and P < .05 was considered statistically significant. RESULTS: An MSAFP level at least 2.5 multiples of the median (MoM) was found in two of 65 cases (3.1%) and in 27 of 1943 women (1.4%) in the rest of the cohort, a nonsignificant difference (relative risk [RR] = 2.2; P = .24). The statistical power to identify a significant difference for this RR was .27. An hCG level of at least 2.5 MoM was found in six cases (9.2%) and in 89 (4.6%) of women in the rest of the cohort, also a nonsignificant difference (RR = 2.0; P = .12). The statistical power to identify a significant difference for this RR was .38. The mean (+/-standard deviation) logarithms of the MSAFP and hCG MoMs in the 65 cases (0.039 +/- 0.191 and 0.048 +/- 0.265, respectively) were not significantly different from those in the 325 matched controls (0.006 +/- 0.148 and -0.010 +/- 0.244, respectively; P = .12 and .08, respectively). CONCLUSION: Although a weak association cannot be excluded, this study found no clinically important increase in risk of developing subsequent hypertensive disorders of pregnancy among women with abnormal second-trimester levels of MSAFP or hCG.

Adult↗
PubMed2004

Risk factors for and clinical outcomes of bloodstream infections caused by extended-spectrum beta-lactamase-producing Klebsiella pneumoniae.

OBJECTIVE: To evaluate risk factors and treatment outcomes of bloodstream infections caused by extended-spectrum beta-lactamase-producing Klebsiella pneumoniae (ESBL-KP). DESIGN: Retrospective case-control study. Stored blood isolates of K. pneumoniae were tested for ESBL production by NCCLS guidelines, double-disk synergy test, or both. SETTING: A 1,500-bed, tertiary-care university hospital and referral center. PATIENTS: Sixty case-patients with bacteremia due to ESB-KP were compared with 60 matched control-patients with non-ESBL-KP. RESULTS: There were no significant differences in age, gender, APACHE II score, or underlying diseases between the groups. Independent risk factors for infections caused by ESBL-KP were urinary catheterization, invasive procedure within the previous 72 hours, and an increasing number of antibiotics administered within the previous 30 days. Complete response rate, evaluated 72 hours after initial antimicrobial therapy, was higher among control-patients (13.3% vs 36.7%; P = .003). Treatment failure rate was higher among case-patients (35.0% vs 15%; P = .011). Overall 30-day mortality rate was 30% for case-patients and 28.3% for control-patients (P = .841). Case-patients who received imipenem or ciprofloxacin as a definitive antibiotic had 10.5% mortality. The mortality rate for initially ineffective therapy was no higher than that for initially effective therapy (9.1% vs 11.1%; P = 1.000), but statistical power was low for evaluating mortality in the absence of septic shock. CONCLUSION: For K. pneumoniae bacteremia, patients with ESBL-KP had a higher initial treatment failure rate but did not have higher mortality if antimicrobial therapy was appropriately adjusted in this study with limited statistical power.

Adolescent↗
PubMed2001

Selected issues in the design and analysis of sport performance research.

The aim of this review is to discuss some issues in the design and statistical analysis of sport performance research, rather than to supply an authoritative 'cookbook' of methods. In general, we try to communicate some possible solutions to the conundrum of how to maintain both internal and external validity, as well as optimize statistical power, in applied sport performance research. We start by arguing that some sport performance research has been overly concerned with physiological predictors of performance, at the expense of not providing a valid and reliable description of the exact nature of the task in question. We show how the influence of certain factors on competitive performances can be described using linear or logistic regression. We discuss the choice of analysis for factorial repeated-measures designs, which is complicated by the assumption of 'sphericity' in a univariate general linear model, and the relatively low statistical power of the multivariate approach when used with small samples. We consider a little-used and simpler technique known as 'analysis of summary statistics'. In multi-group pre- and post-test designs, a useful technique can be to pair-match individuals on their performance scores in a counterbalanced fashion before the intervention or control has been introduced. Finally, we outline how confidence intervals can help in making statements about the probability of the population difference in performance exceeding the value designated as being worthwhile or not.

Humans↗
PubMed2006

The value of relatives with phenotypes but missing genotypes in association studies for quantitative traits.

The additional statistical power of association studies for quantitative traits was derived when ungenotyped relatives with phenotypes are included in the analysis. It was shown that the extra power is a simple function of the coefficient of additive genetic relationship and the phenotypic correlation coefficient between the genotyped and ungenotyped relatives. For close relatives, such as pairs of fullsibs and identical twin pairs, gains in power in the range of 10 to 30% are achieved if only one of the pair is genotyped. The theoretical results were verified by simulations. It was shown that ignoring the error in estimating the genotype of the ungenotyped relative has little impact on the estimates and on statistical power, consistent with results from quantitative trait loci (QTL) linkage studies. For genome-wide association studies in which not all relatives with phenotypes can be genotyped, our study provides a prediction of the additional power of an analysis that includes phenotypes on ungenotyped individuals, and can be used in experimental design. We show that a two-step procedure, in which missing genotypes are imputed and subsequently an association analysis is performed, is efficient and powerful.

Genetic Predisposition to Disease↗
PubMed2000

Sister chromatid exchanges in peripheral lymphocytes from women with carcinoma of the uterine cervix.

Sister chromatid exchanges (SCE) are reciprocal exchanges between sister chromatids. It has been reported that in patients with cervical cancer, the frequency of SCE in peripheral lymphocytes is significantly higher than that in normal individuals; however, other studies have shown no significant difference. The aim of this unmatched case-control study was to compare the mean number of SCE per metaphase in lymphocytes from women with and without carcinoma of the cervix uteri. The SCE specimens were prepared by the fluorescence plus giemsa technique in peripheral lymphocytes from 28 women with carcinoma of cervix uteri and 28 controls. The mean number of SCE per metaphase in women with carcinoma of cervix uteri (7.80 +/- 1.05) was higher than the control group (6.98 +/- 1.13) (P < 0.05; t-test). This study had a statistical power of 0.80 and an alpha value of 0.05. This finding suggests that an increased number of SCE in peripheral lymphocytes is associated with cervical cancer. We consider that the lack of reported association of SCE and cervical cancer might be attributed to the none determination of the statistical power and sample size.

Adult↗
PubMed1995

A randomized evaluation of a computer-based physician's workstation: design considerations and baseline results.

We are performing a randomized, controlled trial of a Physician's Workstation (PWS), an ambulatory care information system, developed for use in the General Medical Clinic (GMC) of the Palo Alto VA. Goals for the project include selecting appropriate outcome variables and developing a statistically powerful experimental design with a limited number of subjects. As PWS provides real-time drug-ordering advice, we retrospectively examined drug costs and drug-drug interactions in order to select outcome variables sensitive to our short-term intervention as well as to estimate the statistical efficiency of alternative design possibilities. Drug cost data revealed the mean daily cost per physician per patient was 99.3 cents +/- 13.4 cents, with a range from 0.77 cent to 1.37 cents. The rate of major interactions per prescription for each physician was 2.9% +/- 1%, with a range from 1.5% to 4.8%. Based on these baseline analyses, we selected a two-period parallel design for the evaluation, which maximized statistical power while minimizing sources of bias.

Ambulatory Care Information Systems↗
PubMed1999

Factors influencing the optimal control-to-case ratio in matched case-control studies.

Statistical power in matched case-control studies depends on both the correlation coefficient between cases and their matched controls (phi) and the prevalence of exposure among controls (P0). To examine the hypothesis that the value of increasing the control-to-case ratio beyond 5 varies with both phi and P0, the authors estimated statistical power for a hypothetical case-control study under different assumptions. The effect of increasing the control-to-case ratio depended on phi and, to a lesser extent, on P0. The results suggest that investigators consider including more than five controls per case when either phi is greater than about 0.2 or P, is less than about 0.15.

Bias↗
PubMed2002

No evidence for short or long term morbidity after increased titer measles vaccination in Sudan.

BACKGROUND: Increased mortality rates have been reported after high titer measles [>10(5.0) plaque-forming units (PFU)] vaccination in several large studies in the developing world. An increased titer measles vaccine study conducted in Sudan included a prolonged prospective evaluation of childhood morbidity after vaccination. METHODS: Five hundred ten children (170 per group) were randomized to receive 1 of 3 regimens at 5 and 9 months of age: (1) meningococcal vaccine, then standard titer (50% tissue culture-infective dose, 103.8) Schwarz measles vaccine; (2) increased titer (10(4.7) PFU) Edmonston-Zagreb measles vaccine followed by meningococcal vaccine; and (3) increased titer (10(4.7) PFU) Connaught vaccine followed by standard titer Schwarz measles vaccine. RESULTS: Health workers collected information at 31,582 semi-monthly and monthly visits during 5 years. No increase in infant mortality was observed, but the statistical power was limited. There were 13, 13 and 10 deaths in the Schwarz, Edmonston-Zagreb and Connaught groups, respectively. There were no differences in duration or incidence of illness between groups at any time during the 5-year follow-up, with comparisons stratified by age and sex. Statistical power for each pairwise comparison was good, with at least 80% power to detect a difference of 1 day per month of illness and a 12% difference in the proportion of visits with an illness recorded. CONCLUSIONS: We were unable to document increased morbidity in recipients of the increased titer measles vaccines used in this study. These data do not support the hypothesis that increased mortality after increased titer vaccine exposure is the result of increased and cumulative morbidity.

Age Factors↗
PubMed1998

Clinical significance not statistical significance: a simple Bayesian alternative to p values.

OBJECTIVES: To take the common "Bayesian" interpretation of conventional confidence intervals to its logical conclusion, and hence to derive a simple, intuitive way to interpret the results of public health and clinical studies. DESIGN AND SETTING: The theoretical basis and practicalities of the approach advocated is at first explained and then its use is illustrated by referring to the interpretation of a real historical cohort study. The study considered compared survival on haemodialysis (HD) with that on continuous ambulatory peritoneal dialysis (CAPD) in 389 patients dialysed for end stage renal disease in Leicestershire between 1974 and 1985. Careful interpretation of the study was essential. This was because although it had relatively low statistical power, it represented all of the data that were available at the time and it had to inform a critical clinical policy decision: whether or not to continue putting the majority of new patients onto CAPD. MEASUREMENTS AND ANALYSIS: Conventional confidence intervals are often interpreted using subjective probability. For example, 95% confidence intervals are commonly understood to represent a range of values within which one may be 95% certain that the true value of whatever one is estimating really lies. Such an interpretation is fundamentally incorrect within the framework of conventional, frequency-based, statistics. However, it is valid as a statement of Bayesian posterior probability, provided that the prior distribution that represents pre-existing beliefs is uniform, which means flat, on the scale of the main outcome variable. This means that there is a limited equivalence between conventional and Bayesian statistics, which can be used to draw simple Bayesian style statistical inferences from a standard analysis. The advantage of such an approach is that it permits intuitive inferential statements to be made that cannot be made within a conventional framework and this can help to ensure that logical decisions are taken on the basis of study results. In the particular practical example described, this approach is applied in the context of an analysis based upon proportional hazards (Cox) regression. MAIN RESULTS AND CONCLUSIONS: The approach proposed expresses conclusions in a manner that is believed to be a helpful adjunct to more conventional inferential statements. It is of greatest value in those situations in which statistical significance may bear little relation to clinical significance and a conventional analysis using p values is liable to be misleading. Perhaps most importantly, this includes circumstances in which an important public health or clinical decision must be based upon a study that has unavoidably low statistical power. However, it is also useful in situations in which a decision must be based upon a large study that indicates that an effect that is highly statistically significant seems too small to be of practical relevance. In the illustrative example described, the approach helped in making a decision regarding the use of CAPD in Leicestershire during the latter half of the 1980s.

Bayes Theorem↗
PubMed2004

Joint mapping of quantitative trait Loci for multiple binary characters.

Joint mapping for multiple quantitative traits has shed new light on genetic mapping by pinpointing pleiotropic effects and close linkage. Joint mapping also can improve statistical power of QTL detection. However, such a joint mapping procedure has not been available for discrete traits. Most disease resistance traits are measured as one or more discrete characters. These discrete characters are often correlated. Joint mapping for multiple binary disease traits may provide an opportunity to explore pleiotropic effects and increase the statistical power of detecting disease loci. We develop a maximum-likelihood method for mapping multiple binary traits. We postulate a set of multivariate normal disease liabilities, each contributing to the phenotypic variance of one disease trait. The underlying liabilities are linked to the binary phenotypes through some underlying thresholds. The new method actually maps loci for the variation of multivariate normal liabilities. As a result, we are able to take advantage of existing methods of joint mapping for quantitative traits. We treat the multivariate liabilities as missing values so that an expectation-maximization (EM) algorithm can be applied here. We also extend the method to joint mapping for both discrete and continuous traits. Efficiency of the method is demonstrated using simulated data. We also apply the new method to a set of real data and detect several loci responsible for blast resistance in rice.

Algorithms↗
PubMed2004

Musculoskeletal parameters of muscles crossing the shoulder and elbow and the effect of sarcomere length sample size on estimation of optimal muscle length.

BACKGROUND: Knowledge of musculoskeletal parameters is essential to understanding and modeling a muscle's force generating capability. A study of musculoskeletal parameters was conducted in two parts: (I) Empirical measurement of upper extremity musculoskeletal parameters. (II) Computational bootstrap simulation to examine statistical power of detecting optimal muscle length as a function of sarcomere length sample size and effect size. METHODS: Parameters were determined with a cadaver model. Sarcomere lengths were measured for 120 samples per muscle using laser diffraction and the mean sarcomere length used to estimate optimal muscle length. A bootstrap computational simulation was conducted to estimate variance in mean sarcomere length as a function of sample size. Statistical power for detecting optimal muscle length as a function of sample size and effect size was then determined. FINDINGS: Parameters are reported in tabular format. Power is 80% at approximately 85, 50, 40 and 25 samples for effect sizes of 0.5, 0.75, 1.0 and 1.5 mm respectively. INTERPRETATION: Musculoskeletal parameters for predicting muscle forces can be adequately measured in a cadaver model. Measurement of 40-60 sarcomere lengths per muscle is sufficient to calculate mean sarcomere length for estimating optimal muscle length with power of 80% for an effect size of 0.75-1.0 mm.

Adult↗