Data Preparation

Linear regression is a linear approach to modeling the relationship between a dependent variable and one or more independent variables. The case of one explanatory variable is called (simple) linear regression. For more than one explanatory variable, the process is called multiple linear regression.

1. Functionalities

  • To upload a data file, preview data set, and check the correctness of data input
  • To pre-process some variables (when necessary) for building the model
  • To calculate the basic descriptive statistics and draw plots of the variables

2. About your data (training set)

  • Your data need to include one dependent variable (denoted as Y) and at least one independent variables (denoted as X)
  • Your data need to have more rows than columns
  • Do not mix character and numbers in the same column
  • The data used to build a model is called a training set

Case Example

  • Suppose in one study, the doctors recorded the birth weight of 10 infants, together with age (month), age group (a: age < 4 months, b; otherwise), and SBP. We were interested (1) to predict the birth weight of infants, and (2) find the relations between birth weight and the other variables, that is, to find out which variable contributes significantly to the dependent variable.

    Please follow the Steps, and Outputs will give real-time analytical results. After getting data ready, please build the model in the next tab.


  • Training Set Preparation




    Upload data will cover the example data

    Please refer to the example data format to upload new data

    2. Show 1st row as column names?

    3. Use 1st column as row names? (No duplicates)

    Correct separator and quote ensure the successful data input

    Find some example data here


    Change the types of some variable?

    Change the referential level for categorical variable?

    2. Input the referential level, each line for one variable






    Output 1. Data Information

    Data Preview

    Variable types


    Output 2. Descriptive Results


    1. For numeric variable

    2. For categorical variable


    Linear fitting plot: to roughly show the linear relation between any two numeric variable. Grey area is 95% confidence interval.


    3. Change the labels of X and Y axes


    Histogram: to roughly show the probability distribution of a variable by depicting the frequencies of observations occurring in certain ranges of values.

    Density plot: to show the distribution of a variable


    Histogram

    When the number of bins is 0, plot will use the default number of bins

    Density plot


    Linear Regression

    1. Functionalities

  • Build the model
    • To build a simple or multiple linear regression model
    • To achieve the estimates of regressions, including (1) estimate of coefficients with t test, p value, and 95% CI, (2) R2 and adjusted R2, and (3) F-Test for overall significance in regression
    • To achieve additional information: (1) predicted dependent variable and residuals, (2) ANOVA table of the model, (3) AIC-based variable selection, and (4) diagnostic plot-based from the residuals and predicted dependent variable
    • To upload new data and get the prediction
    • To achieve the evaluation of new data contains new dependent variable

    2. About your data (training set)

    • The dependent variable is real-valued and continuous under an underlying normal distribution.
    • Please prepare the training set data in the previous Data tab
    • New data (test set) should cover all the independent variables used in the model.

    Please follow the Steps to build the model, and click Outputs to get analytical results.


    Build the Model

    Prepare the data in the previous tab


    Step 1. Choose variables to build the model


    Step 2. Check the model and generate results

    Valid model example: Y ~ X1 + X2
    
                  

    '-1' in the formula indicates that the intercept/constant term has been removed


    Step 3. If data and model are ready, click the blue button to generate model results.





    Output 1. Data Preview


    
                    

    Please edit data in Data tab


    Output 2. Model Results


    Explanations
    • The values for each variable are: estimated coefficients (95% confidence interval), T statistic (t = ) , and P value (p = ) for the significance of each variable
    • T test of each variable and P < 0.05 indicate this variable is statistically significant to the model
    • Observations show the number of samples
    • R2 (R2) is a goodness-of-fit measure for linear regression models and indicates the percentage of the variance in the dependent variable that the independent variables explain collectively. Suppose R2 = 0.49. This result implies that 49% of the variability of the dependent variable has been accounted for, and the remaining 51% is still unaccounted for.
    • Adjusted R2 (adjusted R2) is used to compare the goodness-of-fit for regression models that contain different numbers of independent variables.
    • F statistic (F-Test for overall significance in regression) judges on multiple coefficients taken together at the same time. F=(R^2/(k-1))/(1-R^2)/(n-k); n is sample size; k is number of variable + constant term

    Results

    Save into CSV Save LaTex codes


    Explanations
    • DFvariable = 1
    • DFresidual = [number of sample values] - [number of variables] -1
    • MS = SS/DF
    • F = MSvariable / MSresidual
    • P Value < 0.05: the variable is significant to the model.

    ANOVA Table


    Explanations
    • The Akaike Information Criterion (AIC) is used to performs stepwise model selection.
    • Model fits are ranked according to their AIC values, and the model with the lowest AIC value is sometime considered the 'best'.

    Model selection suggested by AIC

    
                      
                        
                        Save into TXT
                      
                    

    Explanations
    • Q-Q normal plot of residuals checks the normality of residuals. The linearity of the points suggests that the data are normally distributed.
    • Residuals vs fitting plot finds the outliers

    1. Q-Q normal plot of residuals

    2. Residuals vs Fitting plot


    Explanations
    • 3D scatter plot shows the relation between dependent variable (Y), and 2 independent variable (X1, X2)
    • Group variable split the points into groups

    Prediction

    Prepare model first


    Step 4. Test Set Preparation


    Data: Birth Weight


    Data for prediction should cover all the variables in the model

    2. Show 1st row as column names?

    3. Use 1st column as row names? (No duplicates)

    Correct separator and quote ensure the successful data input

    Find some example data here

    Step 5. If the model and new data are ready, click the blue button to generate prediction results.





    Output 3. Prediction Results



    Predicted dependent variable is shown in the 1st column


    Prediction vs True Dependent Variable Plot

    This plot is shown when new dependent variable is provided in the test data.

    This plot shows the relation between predicted dependent variable and new dependent variable, using linear smooth. Grey area is confidence interval.