Statistical Properties of Ratios. I. Empirical Results

Atchley, William R.; Gaskins, C. T.; Anderson, Dwane E.

doi:10.2307/2412740

Cited by 595 publications

(393 citation statements)

References 8 publications

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“…An allometric or linear regression equation is usually very effective in removing the influence of overall size (X) from a data set (e.g. (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

331

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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Section: Relative Corpus Callosum Sizementioning

confidence: 99%

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

Bishop

Wahłsten

1997

Neuroscience & Biobehavioral Reviews

331

160

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“…As in Thomas and Barker (1993), thorax and wing lengths were log transformed for all analyses, and the ratio of wing length to thorax length was analysed as the difference (log wing length -log thorax length) [hereafter referred to as log( W/T)], to reduce statistical problems arising from ratio measures (Atchley et al, 1976). For an overall analysis of variance, lines were treated as random and nested within species x locality.…”

Section: Analysesmentioning

confidence: 99%

Genetic variation and plasticity of thorax length and wing length in Drosophila aldrichi and D. buzzatii

Barker

Krebs

1995

J of Evolutionary Biology

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Reaction norms across three temperatures of development were measured for thorax length, wing length and wing length/thorax length ratio for ten isofemale lines from each of two populations of Drosophila aldrichi and D. huzzatii. Means for thorax and wing length in both species were larger at 24 "C than at either 18 "C or 31 "C, with the reduction in size at 18 "C most likely due to a nutritional constraint. Although females were larger than males, the sexes were not different for wing length/thorax length ratio. The plasticity of the traits differed between species and between populations of each species, with genetic variation in plasticity similar for the two species from one locality, but much higher for D. aldrichi from the other. Estimates of heritabilities for D. aldrichi generally were higher at 18 'C and 24 "C than at 31 "C, but for D. huzatii they were highest at 31 "C, although heritabilities were not significantly different between species at any temperature. Additive genetic variances for D. aldrichi showed trends similar to that for heritability, being highest at 18 "C and decreasing as temperature increased. For D. huzzatii, however, additive genetic variances were lowest at 24 "C. These results are suggestive that genetic variation for body size characters is increased in more stressful environments. Thorax and wing lengths showed significant genetic correlations that were not different between the species, but the genetic correlations between each of these traits and their ratio were significantly different. For D. aldrichi, genetic variation in the wing length/thorax length ratio was due primarily to variation in thorax length, while for D. huszatii, it was due primarily to variation

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“…To work these out, the averages of the foam and feed concentrations were used as each sample was analysed in triplicates. This increased the complexity of statistical analysis as the act of introducing ratios has been see to increase right skewness as well as non-normality (when the coefficient of variance of the denominator is large) [18,19].…”

Section: Discussionmentioning

confidence: 99%