FilionDutilleulPotvin2000

Référence

Filion, M., Dutilleul, P., Potvin, C. (2000) Optimum experimental design for free-air carbon dioxide enrichment (FACE) studies. Global Change Biology, 6(7):843-854.

Résumé

This article presents the logical reasoning underlying the optimal design of an experiment. We used Free-Air Carbon dioxide Enrichment (FACE) experiments to illustrate this trade-off as such experiments are particularly costly. On a theoretical basis, two-way nested designs and split-plot designs have similar power in testing carbon dioxide (CO2) main effects. If researchers have the choice of adding two replicate rings or two control plots to their experiment, our results show that both options provide a substantial gain in statistical power, with a slightly greater gain in the former case and at reduced financial cost in the latter. The former option, however, provides an insurance against possible ring failure. On an empirical basis, we analysed a preliminary FACE photosynthesis dataset collected at Duke University. The experiment was designed as a split-plot design to test the effects of growth environment (GROWTH) and measurement CO2 concentration (MEAS) on photosynthetic rates of loblolly pine. Although a significant effect of MEAS was observed, we failed to detect a significant main effect of GROWTH. Power analysis was used to understand why the GROWTH main effect was not significant. The minimum detectable difference between treatment means that we calculated for GROWTH in this experiment was 4.04 ?mol CO2 m-2 s-1 for a statistical power of 0.90, whereas the observed difference was 0.16 ?mol CO2 m-2 s-1. Our recommendations for the design of FACE experiments are: (i) consider a second treatment factor with many levels within each ring in order to obtain a split-plot design that provides a powerful test of interaction between treatment factors; (ii) add control plots, unless financial constrictions disallow for necessary personnel; (3) pool the data of FACE experiments conducted in comparable ecosystems (e.g. forests or grasslands), with two rings per treatment level at each site.

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@ARTICLE { FilionDutilleulPotvin2000,
    AUTHOR = { Filion, M. and Dutilleul, P. and Potvin, C. },
    TITLE = { Optimum experimental design for free-air carbon dioxide enrichment (FACE) studies },
    JOURNAL = { Global Change Biology },
    YEAR = { 2000 },
    VOLUME = { 6 },
    PAGES = { 843-854 },
    NUMBER = { 7 },
    NOTE = { 13541013 (ISSN) Cited By (since 1996): 21 Export Date: 26 April 2007 Source: Scopus doi: 10.1046/j.1365-2486.2000.00353.x Language of Original Document: English Correspondence Address: Potvin, C.; Department of Biology; McGill University; 1205 Avenue Dr Penfield Montreal, Que., Canada; email: czcp@musica.mcgill.ca References: Dixon, W.J., Massey F.J., Jr., (1969) Introduction to Statistical Analysis, 3rd Edn, , McGraw-Hill, New York; Dutilleul, P., Spatial heterogeneity and the design of ecological field experiments (1993) Ecology, 74, pp. 1646-1658; Dutilleul, P., Potvin, C., Among-environment heteroscedasticity and genetic autocorrelation: Implications for the study of phenotypic plasticity (1995) Genetics, 139, pp. 1815-1829; Ellsworth, D.S., CO2 enrichment in a maturing pine forest: Are CO2 exchange and water status in the canopy affected? (1999) Plant, Cell and Environment, 25, pp. 461-472; Hendrey, G.R., Ellsworth, D.S., Lewin, K.F., Nagy, J., A free-air enrichment system for exposing tall forest vegetation to elevated atmospheric CO2 (1999) Global Change Biology, 5, pp. 293-310; Hurlbert, S.H., Pseudoreplication and the design of ecological field experiments (1984) Ecological Monographs, 54, pp. 187-211; The terrestrial carbon cycle: Implications for the Kyoto Protocol (1998) Science, 280, pp. 1393-1394; Lee, C.S., Rawlings, J.O., Design of experiments in growth chambers: Uniformity trials in the North Carolina State University phytotron (1982) Crop Science, 3, pp. 551-558; Potvin, C., ANOVA: Experiments layout and analysis (2000) Design and Analysis of Ecological Experiments, 2nd Edn, , (eds Scheiner S, Gurevitch J). Kluwer, Dordrecht, in press; Potvin, C., Lechowicz, M.J., Tardif, S., The statistical analysis of ecophysiological response curves obtained from experiments involving repeated measures (1990) Ecology, 71, pp. 1389-1400; (1997) Statistics, Version 7, , SAS Institute, Cary, NC; Sokal, R.R., Rohlf, F.J., (1995) Biometry, 3rd Edn, , Freeman, New York; Steel, R.G.D., Torrie, J.H., (1980) Principles and Procedures of Statistics, 2nd Edn, , McGraw-Hill, New York; Underwood, A.J., (1997) Experiments in Ecology: Their Logical Design and Interpretation Using Analysis of Variance, , Cambridge University Press, New York; Winer, B.J., (1971) Statistical Principles in Experimental Design, 2nd Edn, , McGraw-Hill, New York. },
    ABSTRACT = { This article presents the logical reasoning underlying the optimal design of an experiment. We used Free-Air Carbon dioxide Enrichment (FACE) experiments to illustrate this trade-off as such experiments are particularly costly. On a theoretical basis, two-way nested designs and split-plot designs have similar power in testing carbon dioxide (CO2) main effects. If researchers have the choice of adding two replicate rings or two control plots to their experiment, our results show that both options provide a substantial gain in statistical power, with a slightly greater gain in the former case and at reduced financial cost in the latter. The former option, however, provides an insurance against possible ring failure. On an empirical basis, we analysed a preliminary FACE photosynthesis dataset collected at Duke University. The experiment was designed as a split-plot design to test the effects of growth environment (GROWTH) and measurement CO2 concentration (MEAS) on photosynthetic rates of loblolly pine. Although a significant effect of MEAS was observed, we failed to detect a significant main effect of GROWTH. Power analysis was used to understand why the GROWTH main effect was not significant. The minimum detectable difference between treatment means that we calculated for GROWTH in this experiment was 4.04 ?mol CO2 m-2 s-1 for a statistical power of 0.90, whereas the observed difference was 0.16 ?mol CO2 m-2 s-1. Our recommendations for the design of FACE experiments are: (i) consider a second treatment factor with many levels within each ring in order to obtain a split-plot design that provides a powerful test of interaction between treatment factors; (ii) add control plots, unless financial constrictions disallow for necessary personnel; (3) pool the data of FACE experiments conducted in comparable ecosystems (e.g. forests or grasslands), with two rings per treatment level at each site. },
    KEYWORDS = { FACE Optimal experimental design Power analysis carbon dioxide enrichment experimental design },
    OWNER = { brugerolles },
    TIMESTAMP = { 2007.12.05 },
}

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