Is the assumption of conditional independence fulfilled (based on 2D scatterplot)?












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How do I find out based on a scatterplot, if the assumption of conditional independence is fulfilled? I'd be glad about example plots for the following cases:



Case 1: categorical Y, two numerical predictors: conditional independence fulfilled
Case 2: categorical Y, two numerical predictors: conditional independence NOT fulfilled





Below, I provide plots that (I think would fit these 2 cases) but I would like to confirm:



Case 1: scatterplot



For each class, the points seem like a "cloud" of points with almost no trend and no correlation. Hence, given the class Y the two predictor variables (almost) seem independent. Consequently, the assumption of conditional independence seems fulfilled.



Case 2: scatterplot



Consider Y = "setosa" (red points) only. There seems to be a positive linear relationship between the two predictor variables, i.e. they are correlated and not independent. Consequently, the assumption of conditional independence seems NOT fulfilled (although one might argue that it is fulfilled for the other class "virginica").



Is my understanding correct? If not, I'd be glad about an explanation and example plots that do represent the above mentioned cases.





To reproduce the plots in R:



library(ggplot2)

df = iris[-which(iris$Species == "versicolor"), ]
ggplot(df, aes(x = Petal.Width, y = Petal.Length, color = Species)) + geom_point()
ggplot(df, aes(x = Sepal.Width, y = Sepal.Length, color = Species)) + geom_point()









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    0












    $begingroup$


    How do I find out based on a scatterplot, if the assumption of conditional independence is fulfilled? I'd be glad about example plots for the following cases:



    Case 1: categorical Y, two numerical predictors: conditional independence fulfilled
    Case 2: categorical Y, two numerical predictors: conditional independence NOT fulfilled





    Below, I provide plots that (I think would fit these 2 cases) but I would like to confirm:



    Case 1: scatterplot



    For each class, the points seem like a "cloud" of points with almost no trend and no correlation. Hence, given the class Y the two predictor variables (almost) seem independent. Consequently, the assumption of conditional independence seems fulfilled.



    Case 2: scatterplot



    Consider Y = "setosa" (red points) only. There seems to be a positive linear relationship between the two predictor variables, i.e. they are correlated and not independent. Consequently, the assumption of conditional independence seems NOT fulfilled (although one might argue that it is fulfilled for the other class "virginica").



    Is my understanding correct? If not, I'd be glad about an explanation and example plots that do represent the above mentioned cases.





    To reproduce the plots in R:



    library(ggplot2)

    df = iris[-which(iris$Species == "versicolor"), ]
    ggplot(df, aes(x = Petal.Width, y = Petal.Length, color = Species)) + geom_point()
    ggplot(df, aes(x = Sepal.Width, y = Sepal.Length, color = Species)) + geom_point()









    share|cite|improve this question









    $endgroup$















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      $begingroup$


      How do I find out based on a scatterplot, if the assumption of conditional independence is fulfilled? I'd be glad about example plots for the following cases:



      Case 1: categorical Y, two numerical predictors: conditional independence fulfilled
      Case 2: categorical Y, two numerical predictors: conditional independence NOT fulfilled





      Below, I provide plots that (I think would fit these 2 cases) but I would like to confirm:



      Case 1: scatterplot



      For each class, the points seem like a "cloud" of points with almost no trend and no correlation. Hence, given the class Y the two predictor variables (almost) seem independent. Consequently, the assumption of conditional independence seems fulfilled.



      Case 2: scatterplot



      Consider Y = "setosa" (red points) only. There seems to be a positive linear relationship between the two predictor variables, i.e. they are correlated and not independent. Consequently, the assumption of conditional independence seems NOT fulfilled (although one might argue that it is fulfilled for the other class "virginica").



      Is my understanding correct? If not, I'd be glad about an explanation and example plots that do represent the above mentioned cases.





      To reproduce the plots in R:



      library(ggplot2)

      df = iris[-which(iris$Species == "versicolor"), ]
      ggplot(df, aes(x = Petal.Width, y = Petal.Length, color = Species)) + geom_point()
      ggplot(df, aes(x = Sepal.Width, y = Sepal.Length, color = Species)) + geom_point()









      share|cite|improve this question









      $endgroup$




      How do I find out based on a scatterplot, if the assumption of conditional independence is fulfilled? I'd be glad about example plots for the following cases:



      Case 1: categorical Y, two numerical predictors: conditional independence fulfilled
      Case 2: categorical Y, two numerical predictors: conditional independence NOT fulfilled





      Below, I provide plots that (I think would fit these 2 cases) but I would like to confirm:



      Case 1: scatterplot



      For each class, the points seem like a "cloud" of points with almost no trend and no correlation. Hence, given the class Y the two predictor variables (almost) seem independent. Consequently, the assumption of conditional independence seems fulfilled.



      Case 2: scatterplot



      Consider Y = "setosa" (red points) only. There seems to be a positive linear relationship between the two predictor variables, i.e. they are correlated and not independent. Consequently, the assumption of conditional independence seems NOT fulfilled (although one might argue that it is fulfilled for the other class "virginica").



      Is my understanding correct? If not, I'd be glad about an explanation and example plots that do represent the above mentioned cases.





      To reproduce the plots in R:



      library(ggplot2)

      df = iris[-which(iris$Species == "versicolor"), ]
      ggplot(df, aes(x = Petal.Width, y = Petal.Length, color = Species)) + geom_point()
      ggplot(df, aes(x = Sepal.Width, y = Sepal.Length, color = Species)) + geom_point()






      independence conditional-probability






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      asked Dec 28 '18 at 13:09









      jollyplatypusjollyplatypus

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