The Misuse of Ratios, Indices, and Percentages in Ecophysiological Research

Packard, Gary C.; Boardman, Thomas J.

doi:10.1086/physzool.61.1.30163730

Cited by 441 publications

(284 citation statements)

References 15 publications

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“…31,32 This approach is useful because it makes no prior assumptions about the nature of the scaling relationships between different body compartments and metabolism, but rather derives these empirically using the actual data. The generalised linear model for ANCOVA includes the assumption that the effects of body mass or fat-free mass on metabolic rate are linear and the traits are normally distributed.…”

Section: Comparison Of Energy Expenditure In Lean and Obese Animalsmentioning

confidence: 99%

Some mathematical and technical issues in the measurement and interpretation of open-circuit indirect calorimetry in small animals

et al. 2006

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Indirect calorimetry is increasingly used to investigate why compounds or genetic manipulations affect body weight or composition in small animals. This review introduces the principles of indirect (primarily open-circuit) calorimetry and explains some common misunderstandings. It is not widely understood that in open-circuit systems in which carbon dioxide (CO 2 ) is not removed from the air leaving the respiratory chamber, measurement of airflow out of the chamber and its oxygen (O 2 ) content paradoxically allows a more reliable estimate of energy expenditure (EE) than of O 2 consumption. If the CO 2 content of the exiting air is also measured, both O 2 consumption and CO 2 production, and hence respiratory quotient (RQ), can be calculated. Respiratory quotient coupled with nitrogen excretion allows the calculation of the relative combustion of the macronutrients only if measurements are over a period where interconversions of macronutrients that alter their pool sizes can be ignored. Changes in rates of O 2 consumption and CO 2 production are not instantly reflected in changes in the concentrations of O 2 and CO 2 in the air leaving the respiratory chamber. Consequently, unless air-flow is high and chamber size is small, or rates of change of O 2 and CO 2 concentrations are included in the calculations, maxima and minima are underestimated and will appear later than their real times. It is widely appreciated that bigger animals with more body tissue will expend more energy than smaller animals. A major issue is how to compare animals correcting for such differences in body size. Comparison of the EE or O 2 consumption per gram body weight of lean and obese animals is misleading because tissues vary in their energy requirements or in how they influence EE in other ways. Moreover, the contribution of fat to EE is lower than that of lean tissue. Use of metabolic mass for normalisation, based on interspecific scaling exponents (0.75 or 0.66), is similarly flawed. It is best to use analysis of covariance to determine the relationship of EE to body mass or fat-free mass within each group, and then test whether this relationship differs between groups.

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Section: Comparison Of Energy Expenditure In Lean and Obese Animalsmentioning

confidence: 99%

Some mathematical and technical issues in the measurement and interpretation of open-circuit indirect calorimetry in small animals

et al. 2006

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“…(107)), but the ratio Y/X tends to be artifactually correlated with size X and have pronounced skew (6). Results of experiments or group comparisons may be quite misleading when a ratio is employed to adjust for the influences of overall size (40,97).…”

Section: Relative Corpus Callosum Sizementioning

confidence: 99%

Sex Differences in the Human Corpus Callosum: Myth or Reality?

Bishop

Wahłsten

1997

Neuroscience & Biobehavioral Reviews

335

160

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Abstract:It has been claimed that the human corpus callosum shows sex differences, and in particular that the splenium (the posterior portion) is larger in women than in men. Data collected before 1910 from cadavers indicate that, on average, males have larger brains than females and that the average size of their corpus callosum is larger. A meta-analysis of 49 studies published since 1980 reveals no significant sex difference in the size or shape of the splenium of the corpus callosum, whether or not an appropriate adjustment is made for brain size using analysis of covariance or linear regression. It is argued that a simple ratio of corpus callosum size to whole brain size is not an appropriate way to analyse the data and can create a false impression of a sex difference in the corpus callosum. The recent studies, most of which used magnetic resonance imaging (MRI), confirm the earlier findings of larger average brain size and overall corpus callosum size for males. The widespread belief that women have a larger splenium than men and consequently think differently is untenable. Causes of and means to avoid such a false impression in future research are discussed. Keywords: allometry, brain size, effect size, literature review, meta-analysis, morphometry, ratio measures, statistical power Article:IF men and women think differently, their brains must also differ in some way. This holds true, even if the difference emanates largely from experience, because experience changes the brain (39,114). The size of cognitive gender differences has never been very large (58,69), and the difference has almost vanished for several abilities in more recently published reports (47,70). Of course, not all measures of behavior show small sex differences. For example, in the USA, boys possess considerably more knowledge about electronics, automobiles and machinery (58). Among 21 indicators of sexual behavior and sexuality, two (attitude towards casual intercourse and incidence of masturbation) exhibit male-female differences greater than 0.8 standard deviation (95), which is the conventional criterion for a large group difference in psychological research (27), although most (18 out of 21) show differences less than 0.5 standard deviation (SD). However, on tests of cognitive abilities, sex differences are usually small (58). In a review of 287 effect sizes for spatial visualization abilities (118), the average sex difference was 0.37 SD and only one kind of test (mental rotation) met the criterion for even a moderate effect size. For 254 effect sizes involving mathematical performance in 100 published studies, the male average exceeded the female average by only 0.2 SD, but for studies in which the samples were drawn from the general population, females scored slightly better than males (70). Given such small cognitive gender differences, it seems likely that only the most sensitive and refined neurological techniques will be able to locate the relevant difference in brain tissue.Neuroanatomists have scrutinized thousands of pre...

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“…We used total MR with log body mass entered as a covariate for statistical analyses to avoid errors inherent in using indices such as mass-specific MR (e.g. Packard and Boardman, 1988;Hayes, 2001). However, to ease visual comparisons, we still show some mass-specific MR in the figures.…”

Section: Methodsmentioning

confidence: 99%

Basking hamsters reduce resting metabolism, body temperature and energy costs during rewarming from torpor

Geiser

Gasch

Bieber

et al. 2016

Journal of Experimental Biology

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Basking can substantially reduce thermoregulatory energy expenditure of mammals. We tested the hypothesis that the largely white winter fur of hamsters (Phodopus sungorus), originating from Asian steppes, may be related to camouflage to permit sun basking on or near snow. Winter-acclimated hamsters in our study were largely white and had a high proclivity to bask when resting and torpid. Resting hamsters reduced metabolic rate (MR) significantly (>30%) when basking at ambient temperatures (T a ) of ∼15 and 0°C. Interestingly, body temperature (T b ) also was significantly reduced from 34.7±0.6°C (T a 15°C, not basking) to 30.4±2.0°C (T a 0°C, basking), which resulted in an extremely low (<50% of predicted) apparent thermal conductance. Induced torpor (food withheld) during respirometry at T a 15°C occurred on 83.3±36.0% of days and the minimum torpor MR was 36% of basal MR at an average T b of 22.0±2.6°C; movement to the basking lamp occurred at T b <20.0°C. Energy expenditure for rewarming was significantly reduced (by >50%) during radiant heat-assisted rewarming; however, radiant heat per se without an endogenous contribution by animals did not strongly affect metabolism and T b during torpor. Our data show that basking substantially modifies thermal energetics in hamsters, with a drop of resting T b and MR not previously observed and a reduction of rewarming costs. The energy savings afforded by basking in hamsters suggest that this behaviour is of energetic significance not only for mammals living in deserts, where basking is common, but also for P. sungorus and probably other cold-climate mammals.

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The Misuse of Ratios, Indices, and Percentages in Ecophysiological Research

Cited by 441 publications

References 15 publications

Some mathematical and technical issues in the measurement and interpretation of open-circuit indirect calorimetry in small animals

Some mathematical and technical issues in the measurement and interpretation of open-circuit indirect calorimetry in small animals

Sex Differences in the Human Corpus Callosum: Myth or Reality?

Basking hamsters reduce resting metabolism, body temperature and energy costs during rewarming from torpor

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