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Time series transformation
XLSTAT offers four different possibilities for transforming a time series Xt into Yt, (t=1,…,n): Box-Cox transform (fixed or optimised) Box-Cox transformation is used to improve the normality of the time series; the Box-Cox transformation is defined by the following equation: Yt = [ ( X2t - 1 ) / λ , (Xt > 0, λ ≠ 0 ) or (Xt ≥ 0, λ > 0 ) ; ln( Xt ), (Xt > 0, λ = 0) ] XLSTAT accepts a fixed value of...
Smoothing of time series
Several smoothing methods are available in the XLSTAT-Forecast solution. They are described below. Simple exponential smoothing This model is sometimes referred to as Brown's Simple Exponential Smoothing, or the exponentially weighted moving average model. Exponential smoothing is useful when one needs to model a value by simply taking into account past observations. It is called "exponential" because...
Welch and Brown-Forsythe one-way ANOVA
The analysis of variance (ANOVA) allows to determine whether a factor, also called explanatory variable, has a significant effect on a dependent variable. For example, we may test the effects of a factor involving 4 medical treatments on blood pressure. Running a one-way ANOVA on the data would answer the question: “is there at least one treatment which significantly differs from the others? Principles...
Dose effect analysis
What is dose effect analysis Dose effect analysis is simply a Logistic regression (Logit, Probit, complementary Log-log, Gompertz models) used to model the impact of doses of chemical components (for example a medicine or phytosanitary product) on a binary phenomenon (healing, death). Natural mortality in dose effect analysis Natural mortality should be taken into account in order to model the phenomenon...
Youden Plots
What is a Youden plot? Youden (1959) developed a procedure for representing data produced by N laboratories for two similar materials A and B (they can be identical when we want to compare measurement methods, or different but expected to give identical values). The objective here is to simply identify which laboratories are problematic, either because the two measurements performed show an abnormal...
CATA data analysis
What is CATA (check-all-that-apply) analysis? CATA (check-all-that-apply) surveys have become more and more popular for sensory product characterization since 2007, when it was presented by Adams et al. CATA surveys allow to focus on consumers, more representative of the market, instead of trained assessors. They are easy to set up and easy for participants to answer. The principle is that each assessor...
ANOVA (Analysis of variance)
Principles of the Analysis of Variance Analysis of variance (ANOVA) is a tool used to partition the observed variance in a particular variable into components attributable to different sources of variation. Analysis of variance (ANOVA) uses the same conceptual framework as linear regression. The main difference comes from the nature of the explanatory variables: instead of quantitative, here they...
Mann-Kendall Trend Tests
What is the Mann-Kendall test Mann-Kendall trend test is a nonparametric test used to identify a trend in a series, even if there is a seasonal component in the series. Mann-Kendall test history This test is the result of the development of the nonparametric trend test first proposed by Mann (1945). This test was further studied by Kendall (1975) and improved by Hirsch et al (1982, 1984) who allowed...
Statistical Power for ANOVA / ANCOVA / Repeated measures ANOVA
Statistical Power for ANOVA, ANCOVA and Repeated measures ANOVA XLSTAT offers tools to apply analysis of variance (ANOVA), repeated measures analysis of variance and analysis of covariance (ANCOVA). XLSTAT-Power estimates the power or calculates the necessary number of observations associated with these models. What is statistical power for ANOVA, ANCOVA and Repeated measures ANOVA? What is statistical...
DoE for conjoint analysis
Why do we use design of experiments for conjoint analysis The principle of conjoint analysis is to present a set of products (also known as profiles) to the individuals who will rank, rate, or choose some of them. In an ideal analysis, individuals should test all possible products. But it is soon impossible; the capacity of each being limited and the number of combinations increases very rapidly with...