Ratio index variables or ANCOVA? Fisher's cats revisited

Tu, Yu–Kang; Law, Graham; Ellison, George T. H.; Gilthorpe, Mark S.

doi:10.1002/pst.377

Cited by 7 publications

(5 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Ratio variables like these have obscure interpretations and are not robust to confounding bias. (20) Adjusting for total energy intake - as in the multivariable nutrient density model - offers considerably more accurate estimates of average relative causal effects by reducing confounding and reducing the distorting joint effects of the total energy denominator, but nevertheless remains biased.…”

Section: Discussionmentioning

confidence: 99%

Adjustment for energy intake in nutritional research: a causal inference perspective

Tomova

Arnold

Gilthorpe

et al. 2021

Preprint

View full text Add to dashboard Cite

BackgroundFour models are commonly used to adjust for energy intake when estimating the causal effect of a dietary component on an outcome; (1) the ‘standard model’ adjusts for total energy intake, (2) the ‘energy partition model’ adjusts for remaining energy intake, (3) the ‘nutrient density model’ rescales the exposure as a proportion of total energy, and (4) the ‘residual model’ indirectly adjusts for total energy by using a residual. It remains underappreciated that each approach evaluates a different estimand and only partially accounts for proxy confounding by common dietary causes.ObjectiveTo clarify the implied causal estimand and interpretation of each model and evaluate their performance in reducing dietary confounding.DesignSemi-parametric directed acyclic graphs and Monte Carlo simulations were used to identify the estimands and interpretations implied by each model and explore their performance in the absence or presence of dietary confounding.ResultsThe ‘standard model’ and the mathematically identical ‘residual model’ estimate the average relative causal effect (i.e., a ‘substitution’ effect) but provide biased estimates even in the absence of confounding. The ‘energy partition model’ estimates the total causal effect but only provides unbiased estimates in the absence of confounding or when all other nutrients have equal effects on the outcome. The ‘nutrient density model’ has an obscure interpretation but attempts to estimate the average relative causal effect rescaled as a proportion of total energy intake. Accurate estimates of both the total and average relative causal effects may instead be estimated by simultaneously adjusting for all dietary components, an approach we term the ‘all-components model’.ConclusionLack of awareness of the estimand differences and accuracy of the four modelling approaches may explain some of the apparent heterogeneity among existing nutritional studies and raise serious questions regarding the validity of meta-analyses where different estimands have been inappropriately pooled.

show abstract

Section: Discussionmentioning

confidence: 99%

Adjustment for energy intake in nutritional research: a causal inference perspective

Tomova

Arnold

Gilthorpe

et al. 2021

Preprint

View full text Add to dashboard Cite

show abstract

“…If, on the other hand, the two variables are related, the ratio calculation will only successfully demonstrate this relationship if it is linear and crosses the origin (Jackson et al, 1990). ird, ratio use can give rise to spurious correlations if the two variables used are both affected by a common confounding factor (Tu et al, 2010). ese three issues can be avoided, while still using length and diameter measurements as shape proxies, by performing an analysis of covariance (Tu et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

“…ird, ratio use can give rise to spurious correlations if the two variables used are both affected by a common confounding factor (Tu et al, 2010). ese three issues can be avoided, while still using length and diameter measurements as shape proxies, by performing an analysis of covariance (Tu et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Apples before the fall: Does shape stability coincide with maturity?

Christodoulou

Culham

2021

Quant Plant Bio.

View full text Add to dashboard Cite

Fruit shape is the result of the interaction between genetic, epigenetic, environmental factors and stochastic processes. As a core biological descriptor both for taxonomy and horticulture, the point at which shape stability is reached becomes paramount in apple cultivar identification, and authentication in commerce. Twelve apple cultivars were sampled at regular intervals from anthesis to harvest over two growing seasons. Linear and geometric morphometrics were analysed to establish if and when shape stabilised and whether fruit asymmetry influenced this. Shape stability was detected in seven cultivars, four asymmetric and three symmetric. The remaining five did not stabilise. Shape stability, as defined here, is cultivar-dependent, and when it occurs, it is late in the growing season. Geometric morphometrics detected stability more readily than linear, especially in symmetric cultivars. Key shape features are important in apple marketing, giving the distinctness and apparent uniformity between cultivars expected at point of sale.

show abstract

“…Jackson, Harvey, & Somers, 1990). Third, ratio use can give rise to spurious correlations if the two variables used are both affected by a common confounding factor (Tu, Law, Ellison, & Gilthorpe, 2010). These three issues can be avoided, while still using length and diameter measurements as shape proxies, by performing an analysis of covariance (Tu et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

“…Third, ratio use can give rise to spurious correlations if the two variables used are both affected by a common confounding factor (Tu, Law, Ellison, & Gilthorpe, 2010). These three issues can be avoided, while still using length and diameter measurements as shape proxies, by performing an analysis of covariance (Tu et al, 2010). In this work, we aim to investigate if and when fruit shape stabilizes for apple cultivars, whether the timings of this are cultivar-dependent, and if shape stability timings as described through linear morphometrics differ from those described through geometric morphometrics.…”

Section: Introductionmentioning

confidence: 99%

Apples before the fall: does shape stability coincide with maturity?

Christodoulou

Culham

2020

Preprint

View full text Add to dashboard Cite

Fruit shape is the result of the interaction between genetic, epigenetic, environmental factors, and stochastic processes. As a core biological descriptor both for taxonomy and horticulture, the point at which shape stability is reached becomes paramount in apple cultivar identification, and authentication in commerce. Twelve apple cultivars were sampled at regular intervals from anthesis to harvest over two growing seasons. Linear and geometric morphometrics were analyzed to establish if and when shape stabilized and whether fruit asymmetry influenced this. Shape stability was detected in seven cultivars, four asymmetric and three symmetric. The remaining five did not stabilize. Shape stability, as defined here, is cultivar-dependent, and when it occurs, it is late in the growing season. Geometric morphometrics detected stability more readily than linear, especially in symmetric cultivars. Key shape features are important in apple marketing, giving the distinctness and apparent uniformity between cultivars expected at point of sale.

show abstract

Ratio index variables or ANCOVA? Fisher's cats revisited

Cited by 7 publications

References 14 publications

Adjustment for energy intake in nutritional research: a causal inference perspective

Adjustment for energy intake in nutritional research: a causal inference perspective

Apples before the fall: Does shape stability coincide with maturity?

Apples before the fall: does shape stability coincide with maturity?

Contact Info

Product

Resources

About