Use Of Nonparametric Statistics Research Articles

The effective forces transmitted by high-speed, low-amplitude thoracic manipulation.

Twenty asymptomatic volunteers each received three spinal manipulative treatments to the thoracic spine. The treatments consisted of a straight posterior-to-anterior high-speed, low-amplitude thrust to the transverse process of T3-T10 using a reinforced hypothenar contact. All treatments were given by a full-time practicing clinician with 3 years of experience. The primary objective of this study was to quantify local measures of loading applied by the clinician on the volunteers during spinal manipulative treatments and to compare these local measures of loading with previously described global measures. The sparse information on the mechanics of spinal manipulative treatments deals exclusively with global force or pressure measurements. On the basis of these global data, incorrect conclusions may be drawn about the beneficial effects of spinal manipulative therapy, the loading of internal structures, and the risks associated with these treatments. Twenty asymptomatic subjects each received three posterior-to-anterior, high-speed, low-amplitude spinal manipulative treatments to the transverse process of the thoracic spine. Total force, local force, contact area, peak pressure, and average pressure at the contact interface between clinician and subject were measured continuously by use of a thin, flexible pressure pad. Local and global measures of loading were compared and analyzed by use of nonparametric statistics (alpha = 0.01). The average peak total force was 238.2 N. The average peak local force over a target area of 25 mm2 was 5 N, indicating that global measures of loading vastly overestimate the local effective forces at the target site. The peak pressure point moved, on average, 9.8 mm during the course of the manipulation. To the authors' best knowledge, this is the first study to quantify local, effective measures of loading and compare them with the global measures typically used. The conclusions are limited because the study used a single clinician. The effective loading of specific target sites is much smaller than the global measures might suggest. This result occurs because as the forces during spinal manipulative treatment increase, so does the contact area; therefore, much of the total treatment force is taken up by non-target-specific tissues. Because of the vast discrepancy between the global and local measures of loading, it is suggested that risk-benefit assessments of high-speed, low-amplitude spinal manipulative treatments should be made, including local measures of loading. Finally, because theoretical approaches and the inverse dynamics approach can provide only global measures of loading, the results of such studies should be interpreted with caution.

Phasic production of urinary pyridinium crosslinks in mice: the effect of ovariectomy.

Considerable sample to sample variability in deoxypyridinoline crosslink/creatinine (Dpd/CREAT) ratio values was confirmed when twice-weekly sampling for 77 days was performed in C57 mice. Analysis of samples from individual mice indicated that, in the majority of mice in a given group (54-67%), phasic changes occurred with periodic peaks as much as 4-5 times basal values. Alignment of peaks in the individual time courses of mice revealed a clear cyclic crosslink production (periodicity 12-14 days) for the population, although not all mice gave a peak in every case. Ovariectomy (OVX) (compared to sham-operated mice) increased mean values of crosslink production by either C57 or C57 x 129 F1 mice from about 10 days after operation with highest values between 21 and 35 days, and then a decrease in the difference between sham and OVX, particularly in C57 mice. Analysis of both time courses for individual mice and distribution curves of the data from groups of mice indicated that OVX consistently increased basal crosslink values (6-9 ratio units) with phasic peak values superimposed. The peak alignment analysis reinforced this observation. The influence of the background variability was avoided by pooling data over one cycle time and the use of nonparametric statistics, and the effect of OVX was analyzed in several strains of mice. Crosslink levels and phasic production declined with age but were also influenced by manipulation of the mice, suggesting that experimental conditions should be rigorously controlled when this urinary crosslink measure is used as a parameter in mouse models of OVX-induced osteoporosis.

The use of nonparametric statistics in quantitative electron microscopy.

Parametric statistical methods assume samples that have a normal distribution and representative sample sizes (i.e. n >20). Quantitative electron microscopy is inherently restricted to small sample sizes and a priori there is no way to know if the expression of the ligand being studied has a normal distribution. Thus to make statistical inferences based on data generated by quantitative electron microscopy using parametric methods may not be justified. Nonparametric statistical methods offer a tool for the evaluation of data that do not meet the criteria for analysis by parametric methods. In this report I show the utility of using nonparametric statistical methods for the analysis of data generated by quantitative electron microscopy.

Body mass index, waist/hip ratio and androgen—estrogen activity in younger versus older Polish men

This study was performed to evaluate the associations between estradiol, dehydroepiandrosterone sulfate (DHEAS), free and total testosterone levels, and anthropometric parameters of general adiposity (body mass index, BMI) and fat distribution (waist/hip ratio, WHR), separately in two subgroups of healthy Polish men: younger (aged 22–39 years, n = 95) and older (aged 40 years and over, n = 141) subjects. Sex steroid levels were assessed using radioimmunoassay (RIA). BMI was used as a measure of general adiposity. WHR was used to estimate distribution of adipose depots. The relationships between sex steroids, BMI, WHR and age were evaluated by use of non-parametric statistics (Spearman coefficients). Aging was related to a reduction of all hormone levels (correlation coefficients with age: free testosterone r = -0.52, p < 0.001; total testosterone r = -0.25, p < 0.001; estradiol r = -0.18, p < 0.001; DHEAS r = -0.45, p < 0.001) and an increase of BMI and WHR for BMI r = 0.23, p < 0.001; for WHR r = 0.47, p < 0.001). A one way analysis of co-variance (ANCOVA) was applied separately in the two subgroups of subjects to assess the relationships between hormonal and anthropometric variables. In men aged 22–39 years, the total (but not free) testosterone and DHEAS (when controlled for age) significantly differentiated BMI values. In subjects aged 40 years and over, no associations between sex steroids and BMI were revealed. In younger males DHEAS differentiated WHR values (even when controlled for age and BMI), whereas after the age of 40 years an increased WHR was accompanied by increases in both estradiol and DHEAS levels. The associations between the androgen—estrogen activity and the anthropometric parameters of adiposity vary in younger versus older healthy men.

Bone mineral content and androgen-estrogen activity in a population of healthy male inhabitants of Wroclaw, Poland

In this study, age-related changes in bone mineral content (BMC) were investigated in the context of alterations of total testosterone, estradiol and dehydroepiandrosterone sulfate (DHEAS) during normal male aging. An anthropologically homogeneous group of 236 males, aged 22–67 years, was subdivided into eight 5-year age categories. The men were healthy and occupationally active inhabitants of the city of Wroclaw, Lower Silesia, Poland. The investigated hormones were measured using standard immunoassays. Trabecular, cortical and total BMC at the distal radius of the non-dominant hand were separately assessed by peripheral quantitative computed tomography (pQCT) using the Stratec 960 apparatus. All correlations among hormone and densitometric parameters and age were evaluated by use of non-parametric statistics (Spearman coefficient). Reductions in trabecular, cortical and total BMC of approximately 40.0%, 28. 1%and 30.8%, respectively, were found in the peak mass between the age category with maximal BMC values and men aged 55 years and older. The declines in trabecular and total BMC with age appeared to be statistically significant, whereas no analogous correlation between cortical BMC and age was found. We observed a decrease in total testosterone, DHEAS and estradiol levels of approximately 45%, 55% and 32%, respectively, in the maximal concentrations between the age category with peak values and men aged 55 years and older. A distinct decline in hormone levels commenced around 25 years of age. All evaluated steroids demonstrated a significant reduction with age. In our findings, the total testosterone level did not correlate at all with either trabecular, cortical or total BMC at the distal radius. DHEAS levels appeared to be insignificant for mineralization of cortical BMC, whereas a significant correlation was demonstrated between DHEAS and both total (r = 0.18; p = 0.02) and trabecular BMC (r = 0.22; p = 0.003). The last association was the strongest relationship established in the entire study. Estradiol levels, but not total testosterone values, appeared to correlate with all trabecular (r = 0.16; p = 0.02), cortical (r = 0.14; p = 0.04) and total BMC (r = 0.16; p = 0.02) at the distal radius. Total testosterone levels appeared to be insignificant for the degree of age-related changes in male bone mineralization. From the three sex steroids measured in healthy males, the adrenal androgen (dehydroepiandrosterone sulfate) seems to be the best endocrinological measure of the degree of male skeletal mineralization, especially of the trabecular component, which is clearly the most sensitive to all hormonal fluctuations. However, BMC is traditionally associated with gonadalfunctions, and is not always monitored reliably by total testosterone levels (and by concentrations of estradiol, which is usually converted peripherally from testosterone).

Theoretical and Methodological Notes on the Listening Threshold Variable

In a post hoc study conducted on closed files at the Centre of Audio-Psycho-Phonology, the psychometric distributionof Listening Threshold decibel scores was found to be positively skewed, and in some cases bi-modal, necessitating the use of non-parametric statistics for hypothesis testing. The author notes inappropriate statistical usage in previously published studies investigating the Listening Threshold variable. Once correct statistics are applied, and appropriate controls are introduced for expected ceiling and interaction effects, Listening Threshold decibel scores were found to decrease significantly following treatment using the Tomatis remedial listening program.

Inter‐ and intra‐individual variability of non‐invasive tear break‐up time in Hong Kong Chinese

Non-invasive tear break-up time (NITBUT) has been proposed as a measure of tear film integrity which is superior to the more commonly used tear break-up time (TBUT), since it does not alter the volume or the physicochemical properties of the tear layer by the addition of fluorescein. We measured NITBUT by measuring the time taken for distortions or discontinuities to appear in the reflected image of a grid pattern which covered about 80 per cent of the corneal surface. NITBUT measures were made 100 times on seven Hong Kong Chinese subjects with up to 20 consecutive measures being made on a single day. We also measured NITBUT on one occasion on an unselected population of 52 Hong Kong Chinese subjects. NITBUT shows a skewed distribution in all subjects, with many shorter values and some extremely long values. There are statistically significant variations in NITBUT from day to day, and from subject to subject. The group of 52 subjects also had a skewed NITBUT distribution with many short values and some very long values. The arithmetic mean does not adequately represent NITBUT data, either for individual subjects or for this group of subjects. As many as five to eight measures may be necessary to gain a stable estimate of the NITBUT and stability of the measure is improved if extreme values are omitted. We recommend the use of nonparametric statistics to compare NITBUT values from day to day in or between subjects.

The viability of using COCOMO in the special application software bidding and estimating process

The purpose of the author is to correlate actual data with COCOMO (constructive cost model) estimated values and determine if the COCOMO method accurately reflects documented program expenditures. Because spaceborne microprocessing is a relatively new arena, the primary constraint associated with developing a model is the limited available database. Data collection to support a statistical analysis is presented along with a discussion of calculated COCOMO results. In the analysis, the use of nonparametric statistics for small samples is addressed. Wilcoxon Signed-Rank and Kendall-Rank statistics support distribution free analyses of the data.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Aberrant baroreceptor mechanotransduction in adult Dahl rats on low-salt diet.

Single fiber, regularly discharging baroreceptors (n = 118) from adult Dahl salt-sensitive (DS) and salt-resistant (DR) rats on a low-salt diet were studied using an in vitro aortic arch-aortic nerve preparation. Pressure thresholds (Pth) and suprathreshold pressure sensitivities (Sth) were determined from responses to slow ramps of pressure. Pressure-diameter relationships measured in each rat were used to transform Pth and Sth values to their mechanical equivalents in terms of aortic wall strain. DS and DR ages were not different (approximately 50 wk). Despite the low-salt diet, DS tail systolic blood pressures were significantly higher than DR by approximately 25 mmHg. Pth averaged 84 mmHg in DR and 97 mmHg in DS. Sth values were similar in DR and DS (average 1.44 and 1.39 spikes.s-1.mmHg-1 in DR and DS, respectively). Increased variance of baroreceptor properties of DS over DR was a prominent finding and necessitated use of nonparametric statistics. The cumulative distribution of Pth values of DS was significantly different from DR, but Sth values were similar. Thus baroreceptor pressure set points are altered in adult DS, but pressure sensitivity per se is not. The differences in pressure parameters were not eliminated by conversion to their mechanical equivalents. Correlation analysis found only weak relationships between Pth and blood pressure for DS and DR (r less than 0.40). Thus in contrast to previous studies in the spontaneously hypertensive rat model, baroreceptors in adult DS on low salt are characterized by elevated variability and a weaker than expected correlation to the prevailing blood pressure in the animal.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-parametric statistics for nucleic acid sequence study

The use of non-parametric statistics for nucleic acid sequence studies is illustrated by some examples. This method is highly flexible and allows design of specific tests for detecting sequence structure. Tests devoted to local repetitivity, codon nearest neighbors, and dinucleotide avoidance are discussed in detail. An appendix indicates all computations required to use these tests.

Nonparametric Statistics: Use and Nonuse

This paper clarifies the distinctions among parametric, non-parametric, and distribution free statistical tests. The principal circumstances prompting the use of nonparametric procedures, both rank order and qualitative data Techniques, are identified and illustrated. Historical factors and disciplinary orientations affecting the use of nonparametric procedures are discussed. Finally, some conditions which are conducive to the more frequent use of nonparametric statistics are identified.

How One Normally Constructs Good Measures

This article describes how following good measurement construction procedures result in normal variables, for which the use of nonparametric statistics would simply be inappropriate.