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**Logistic regression, survival analysis, model II regression**

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**Logistic regression Response (dependent) variable is either**

yes/ no (alive/ dead, flowering/sterile) Number of positive cases out of total (seed germination, number of flowering individuals out of total no of individuals) – assuming binomial distribution Regression model predicts probability, i.e. value between 0 and 1

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Logistic regression 2 Logit transformation: log( p / (1-p) ) = log (odds ratio) Can not be applied directly to 0/1, applied on predicted probabilities: p in (0, 1) Special case of Generalized linear models (GLM)

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**Logistická regrese a Statistica**

Example – survival of winter depending on flowering and rhizome size Advanced Linear / Nonlinear Models Generalized ... Models Logit model Or non-linear estimation...

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Possible application Example – how is the probability of survival over the winter affected by flowering in previous summer, storage of sugars, and length of the winter? Surmalog.xls, list ReprEff

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**Survival analysis Survival analysis, mainly in medicine**

Useful for data (usually about time) with censoring Most often right censoring: I have finished the experiment, but some individuals are still alive (or did not germinate yet etc.] Left censoring For data without censoring are probably simpler methods available - mostly generalized linear models)

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Survival curve Kaplan-Meier method:

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Míra rizika Hazard rate, l: pravděpodobnost, že jedinec přežije časový úsek t, pokud se jej již dožil Kumulativní funkce míry rizika L(t): ve vztahu ke křivce přežívání platí: L(t) = - log S(t) Využití l u složitějších modelů analýzy přežívání (Coxův model relativního rizika, Cox proportional hazard rate): l(t) = l0(t)*eb0+b1x1+b2x2+…

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**Use of survival analysis?**

Comparison of survival curves among groups Estimate “halftime” (of life, survival time, time to germination) with confidence interval Testing effects of both quantitative and qualitative predictors

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**Survival analysis - exercises**

Germination dynamics affected by chilling, file Surmalog.xls, sheet Germination, method Comparing two samples Effect of radio-collars on survival of antilops -obojků na úmrtnost antilop, file Surmalog.xls, sheet RadioCollars, method Regression / Proportional hazard (Cox) regression

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**Regression model typ II**

In ordinary Least Squares, in dependence of Y on X, vertical differences are minimized (i.e (Y-Ypredicted)2 Similarly, if we study X ~ Y, (X-Xpredicted)2 is minimized. The angel among the two lines decreases with increasing (r) Major axis (MA) regression – symmetric – what is perpendicular depends on units – various standardizations

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**MA regression: motivation**

Zkoumáme vztah mezi délkou (L) a hmotností (M) jedinců určitého druhu Pokud se tvar těla s růstem nemění (isometrický růst), lze vztah popsat takto: M = c*L a po logaritmování: log(M) = b0 + 3*log(L), kde b0 = log(c) Při užití „normální“ regrese bude ale odhadnutý koeficient b1 < 3

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**Alometric biomass partitioning**

Allometric biomass partitioning theory (APT): : Mleaves = b1*Mroots3/4 B.J. Enquist & K.J. Nikolas (2002): Global allocation rules for patterns of biomass partitioning in seed plants. Science 295,

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**MA regression: example**

Vztah biomasy listů a stonků: Mleaves = b1*Mroots3/4 After log transformation, slope should be 0.75 Various herb species RMA program :

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Logistic Regression STA2101/442 F 2014 See last slide for copyright information.

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