Repeated measures experiments in forestry: focus on analysis of response curves

Meredith, Michael P.; Stehman, S. V.

doi:10.1139/x91-133

Cited by 141 publications

(85 citation statements)

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“…As the test for trend in accuracy over time is based on b, the test is limited to assessing the linear component of the relationship of accuracy with time (year). The test for trend is a repeated measures analysis [28] implemented as a parametric test using a one-sample t-test applied to the sample b m,ss observations (the sample size is n ss =number of study sites). Alternatively, a non-parametric version of the test for trend could be implemented using the one-sample non-parametric Wilcoxon test applied to the sample b m,ss observations.…”

Section: Temporal Stability Assessmentmentioning

confidence: 99%

Assessing the Temporal Stability of the Accuracy of a Time Series of Burned Area Products

et al. 2014

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Temporal stability, defined as the change of accuracy through time, is one of the validation aspects required by the Committee on Earth Observation Satellites' Land Product Validation Subgroup. Temporal stability was evaluated for three burned area products: MCD64, Globcarbon, and fire_cci. Traditional accuracy measures, such as overall accuracy and omission and commission error ratios, were computed from reference data for seven years (2001)(2002)(2003)(2004)(2005)(2006)(2007) in seven study sites, located in Angola, Australia, Brazil, Canada, Colombia, Portugal, and South Africa. These accuracy measures served as the basis for the evaluation of temporal stability of each product. Nonparametric tests were constructed to assess different departures from temporal stability, specifically a monotonic trend in accuracy over time (Wilcoxon test for trend), and differences in median accuracy among years (Friedman test). When applied to the three burned area products, these tests did not detect a statistically significant temporal trend or significant differences among years, thus, based on the small sample size of seven sites, there was insufficient evidence to claim these products had temporal instability. Pairwise Wilcoxon tests comparing yearly accuracies provided a measure of the proportion of year-pairs with significant differences and these proportions of significant pairwise differences were in turn used to compare temporal stability between BA products. The proportion of year-pairs with different accuracy (at the 0.05 significance level) ranged from 0% (MCD64) to 14% (fire_cci), OPEN ACCESSRemote Sens. 2014, 6 2051 computed from the 21 year-pairs available. In addition to the analysis of the three real burned area products, the analyses were applied to the accuracy measures computed for four hypothetical burned area products to illustrate the properties of the temporal stability analysis for different hypothetical scenarios of change in accuracy over time. The nonparametric tests were generally successful at detecting the different types of temporal instability designed into the hypothetical scenarios. The current work presents for the first time methods to quantify the temporal stability of BA product accuracies and to alert product end-users that statistically significant temporal instabilities exist. These methods represent diagnostic tools that allow product users to recognize the potential confounding effect of temporal instability on analysis of fire trends and allow map producers to identify anomalies in accuracy over time that may lead to insights for improving fire products. Additionally, we suggest temporal instabilities that could hypothetically appear, caused by for example by failures or changes in sensor data or classification algorithms.

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Section: Temporal Stability Assessmentmentioning

confidence: 99%

Assessing the Temporal Stability of the Accuracy of a Time Series of Burned Area Products

et al. 2014

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“…genotype pair ; the sub-unit in the splitplot design) and were analysed using orthogonal Whole experimental units were the open-top chambers (n l 32) and the subunits were half-chambers consisting of early or late leaf-fall genotype pairs (Gen pair). Corresponding data are shown in Figures 1 and 4. polynomials in repeated measure  to characterize treatmentitime interactions over the duration of the experiment (Meredith & Stehman, 1991). Coefficients of second-order polynomials were calculated according to Robson (1959) for data with unequal sample spacing.…”

Section: Statistical Analysesmentioning

confidence: 99%

“…For example, a significant linear CO # effect (i.e., a significant CO # itime interaction) for fine root production indicated that the rate of fine root production was significantly affected by atmospheric CO # concentration (cf. Meredith & Stehman, 1991). To analyse treatment effects on fine-root life span, cohort survivorship functions were tested using a Gehen-Wilcoxon test for survivorship data in which not all subjects die before the end of the experiment (Pyke & Thompson, 1986).…”

Section: Statistical Analysesmentioning

confidence: 99%

Growth and C allocation of Populus tremuloides genotypes in response to atmospheric CO₂ and soil N availability

et al. 1998

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We grew cuttings of two early (mid Oct.) and two late (early Nov.) leaf-fall Populus tremuloides Michx. genotypes (referred to as genotype pairs) for c. 150 d in open-top chambers to understand how twice-ambient (elevated) CO # and soil N availability would affect growth and C allocation. For the study, we selected genotypes differing in leaf area duration to find out if late-season photosynthesis influenced C allocation to roots. Both elevated CO # and high soil N availability significantly increased estimated whole-tree photosynthesis, but they did so in different ways. Elevated CO # stimulated leaf-level photosynthesis rates, whereas high soil N availability resulted in greater total plant leaf area. The early leaf-fall genotype pair had significantly higher photosynthesis rates per unit leaf area than the late leaf-fall genotype pair and elevated CO # enhanced this difference. The early leaf-fall genotype pair had less leaf area than the late leaf-fall genotype pair, and their rate of leaf area development decreased earlier in the season. Across both genotype pairs, high soil N availability significantly increased fine root length production and mortality by increasing both the amount of root length present, and by decreasing the life span of individual roots. Elevated CO # resulted in significantly increased fine root production and mortality in high N but not low N soil and did not affect fine root life span. The early leaf-fall genotype pair had significantly greater fine root length production than the late leaf-fall genotype pair across all CO # and N treatments. These differences in belowground C allocations are consistent with the hypothesis that belowground C and N cycling is strongly influenced by soil N availability and will increase under elevated atmospheric CO # . In addition, this study reinforces the need for better understanding of the variation in tree responses to elevated CO # , within and among species.

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“…Such a problem can be overcome by fitting the same regression model separately to the data from each experimental unit and then comparing the resulting parameter estimates indirectly by using them as primary data for multivariate analysis (e.g., Fleming and Wood 1996). This allows one to use the preferred regression-based approach without foundering on the autocorrelation in the observations (Meredith and Stehman 1991). Autoregression analysis (e.g., Chatfield 1989) represents another approach to the autocorrelation problem.…”

Section: Autocorrelationmentioning

confidence: 99%

Statistical advantages in, and characteristics of, data from long-term research

Fleming¹

1999

The Forestry Chronicle

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Scientifically, long-term research is the best approach for Scientifiquement parlant, la recherche a long terme constitue investigating phenomena involving slow, subtle, and long-penla meilleure approche pour etudier des phenomenes qui comportent od cyclic change. The importance of such phenomena is emphades changements lents, subtils et repartis sur un cycle tres long. sized by recent work in ecological theory which suggests that they L'irnptance de ces phenomenes est mise en evidence par 1es m t s have a constraining, controlling influence on other faster ecosystravaux sur la theorie ecologique qui laisse entendre qu'ils ont une temprocesses. Four short-term ' ' alternative" approaches (rehmpechve influence contraignante et controlante sur d'autres processus analysis, fast system analogues, simulation models, and spaceecosysterniques plus rapides. Les quatre approches "alternafor-time substitution) each have drawbacks compared to long-term tives" a court terme ( analyse retrospective, analogues rapides de research in studying these kinds of phenomena. Space-for-time systeme, modeles de simulation et substitution espace-temps) ont replication, however, could complement long-term research tous des defauts lorsqu'on les compare a la recherche a long terme well. Various statistical concerns (missing data, autocorrelaalors qu'on veut etudier ce genre de phenomenes. La copie tion, statistical power, precision, bias, and spurious correlation) espace-temps, par contre, pourrait egalement etre un complement are briefly discussed in the context of justification for, and reca la rechmhe a long terme. Les diverses questions statistiques (donommendations during the conduct of, long term research.nees manquantes, autocorrelation, puissance statistique, precision, biais, et fausse correlation) sont brievement discutees dans le conKey words: statistics, long term research, data analysis, statistexte de la justification a des fins, ainsi que des recommandations tical power, space-for-time substitution a suivre au cours, de recherche a long terme.

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Repeated measures experiments in forestry: focus on analysis of response curves

Cited by 141 publications

References 0 publications

Assessing the Temporal Stability of the Accuracy of a Time Series of Burned Area Products

Assessing the Temporal Stability of the Accuracy of a Time Series of Burned Area Products

Growth and C allocation of Populus tremuloides genotypes in response to atmospheric CO₂ and soil N availability

Statistical advantages in, and characteristics of, data from long-term research

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Repeated measures experiments in forestry: focus on analysis of response curves

Cited by 141 publications

References 0 publications

Assessing the Temporal Stability of the Accuracy of a Time Series of Burned Area Products

Assessing the Temporal Stability of the Accuracy of a Time Series of Burned Area Products

Growth and C allocation of Populus tremuloides genotypes in response to atmospheric CO2 and soil N availability

Statistical advantages in, and characteristics of, data from long-term research

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Growth and C allocation of Populus tremuloides genotypes in response to atmospheric CO₂ and soil N availability