Vascular geometry and oxygen diffusion in the vicinity of artery-vein pairs in the kidney.

Renal arterial-to-venous (AV) oxygen shunting limits oxygen delivery to renal tissue. To better understand how oxygen in arterial blood can bypass renal tissue, we quantified the radial geometry of AV pairs and how it differs according to arterial diameter and anatomic location. We then estimated diffusion of oxygen in the vicinity of arteries of typical geometry using a computational model.

Telemetry-based oxygen sensor for continuous monitoring of kidney oxygenation in conscious rats.

The precise roles of hypoxia in the initiation and progression of kidney disease remain unresolved. A major technical limitation has been the absence of methods allowing long-term measurement of kidney tissue oxygen tension (Po₂) in unrestrained animals. We developed a telemetric method for the measurement of kidney tissue Po₂ in unrestrained rats, using carbon paste electrodes (CPEs).

Should we use one-sided or two-sided P values in tests of significance?

'P' stands for the probability, ranging in value from 0 to 1, that results from a test of significance. It can also be regarded as the strength of evidence against the statistical null hypothesis (H₀). When H₀ is evaluated by statistical tests based on distributions such as t, normal or Chi-squared, P can be derived from one tail of the distribution (one-sided or one-tailed P), or it can be derived from both tails (two-sided or two-tailed P).

Analysing 2 × 2 contingency tables: which test is best?

A survey of five journals of physiology or pharmacology for 2011 showed that Fisher's exact test was used three times as frequently as Pearson's Chi-squared test. I shall argue that neither test is appropriate for analysing 2 × 2 tables of frequency in biomedical research. Pearson's test requires that random samples are taken from defined populations.

A primer for biomedical scientists on how to execute model II linear regression analysis.

1. There are two very different ways of executing linear regression analysis. One is Model I, when the x-values are fixed by the experimenter.

Definition of ambulatory blood pressure targets for diagnosis and treatment of hypertension in relation to clinic blood pressure: prospective cohort study.

Background: Twenty-four hour ambulatory blood pressure thresholds have been defined for the diagnosis of mild hypertension but not for its treatment or for other blood pressure thresholds used in the diagnosis of moderate to severe hypertension. We aimed to derive age and sex related ambulatory blood pressure equivalents to clinic blood pressure thresholds for diagnosis and treatment of hypertension.

Methods: We collated 24 hour ambulatory blood pressure data, recorded with validated devices, from 11 centres across six Australian states (n=8575).

Linear regression analysis for comparing two measurers or methods of measurement: but which regression?

1. There are two reasons for wanting to compare measurers or methods of measurement. One is to calibrate one method or measurer against another; the other is to detect bias.

Confidence in Altman-Bland plots: a critical review of the method of differences.

1. Altman and Bland argue that the virtue of plotting differences against averages in method-comparison studies is that 95% confidence limits for the differences can be constructed. These allow authors and readers to judge whether one method of measurement could be substituted for another.

Estimating the risk of rare complications: is the 'rule of three' good enough?

THE CLINICAL PROBLEM: If a surgeon has performed a particular operation on n consecutive patients without major complications, what is the long-term risk of major complications after performing many more such operations? Examples of such operations are endoscopic cholecystectomy, nephrectomy and sympathectomy. THE STATISTICAL PROBLEM AND SOLUTIONS: This general problem has exercised the minds of theoretical statisticians for more than 80 years. They agree only that the long-term risk is best expressed as the upper bound of a 95% confidence interval.

Analysis of 2 x 2 tables of frequencies: matching test to experimental design.

Background: Biomedical investigators often use unsuitable statistical techniques for analysing the 2 x 2 tables that result from their experimental observations. This is because they are confused by the conflicting, and sometimes inaccurate, advice they receive from statistical texts or statistical consultants.

Methods: These consist of a review of published work, and the use of five different statistical procedures to analyse a 2 x 2 table, executed by StatXact 8.

Analysing clinical studies: principles, practice and pitfalls of Kaplan-Meier plots.

The Problem: The conventional method for estimating survival over time following an episode of disease or treatment is the Kaplan-Meier (K-M) technique, which results in a step-down survival plot, with upper and lower bounds of 1.0 and 0, respectively. The mirror image of this plot represents the cumulative incidence of an adverse event, such as death, with lower and upper bounds of 0 and 1.

Outlying observations and missing values: how should they be handled?

1. The problems of, and best solutions for, outlying observations and missing values are very dependent on the sizes of the experimental groups. For original articles published in Clinical and Experimental Pharmacology and Physiology during 2006-2007, the range of group sizes ranged from three to 44 ('small groups').

Statistics in biomedical laboratory and clinical science: applications, issues and pitfalls.

This review is directed at biomedical scientists who want to gain a better understanding of statistics: what tests to use, when, and why. In my view, even during the planning stage of a study it is very important to seek the advice of a qualified biostatistician. When designing and analyzing a study, it is important to construct and test global hypotheses, rather than to make multiple tests on the data.

Writing intelligible English prose for biomedical journals.

1. I present a combination of semi-objective and subjective evidence that the quality of English prose in biomedical scientific writing is deteriorating. 2.

Detecting systematic bias between two raters.

1. I recently reviewed, inter alia, methods for comparing two raters who make judgements on an ordered categorical scale, directed principally at the kappa statistic and its weaknesses. 2.

Peer review of biomedical manuscripts: an update.

There have been published at least two major sets of contributions to the matter of peer review of manuscripts since my last article on this topic. In one, the merits of truly open peer review, in which the names of authors and their affiliations are revealed to reviewers, and the names of reviewers to authors, are extolled. The other contribution is not so original, in that it exhorts biomedical investigators and authors to consult with professional statisticians.

Interim analyses of data as they accumulate in laboratory experimentation.

Background: Techniques for interim analysis, the statistical analysis of results while they are still accumulating, are highly-developed in the setting of clinical trials. But in the setting of laboratory experiments such analyses are usually conducted secretly and with no provisions for the necessary adjustments of the Type I error-rate.

Discussion: Laboratory researchers, from ignorance or by design, often analyse their results before the final number of experimental units (humans, animals, tissues or cells) has been reached.

The Surgical Research Society of Australasia.

Background: The Surgical Research Society of Australasia (SRS) was established in 1961. The main intent was to promote surgical research, especially by young surgeons. The 50th Scientific Meeting of the SRS is due to be held in 2002.

Statistical techniques for comparing measurers and methods of measurement: a critical review.

1. Clinical and experimental pharmacologists and physiologists often wish to compare two methods of measurement, or two measurers. 2.