Error bars are used to indicate the estimated error in a measurement. Errors bars indicate the uncertainty in the x and/or y-values.

Vertical Error Bars

The most common error bar plot is one in which the errors are in the y-values. This example shows such an error bar plot. Note that the values of the low and high arguments are absolute y-values, not relative or percentage values.

 

(Download Code)

 

import com.imsl.chart.*;

import java.awt.Color;

import com.imsl.stat.Random;

 

public class SampleErrorBar extends JFrameChart {

 

    public SampleErrorBar() {

        Random r = new Random(123457);

       

        Chart chart = getChart();

        AxisXY axis = new AxisXY(chart);

       

        // Generate a random data set, with random errors

        int n = 20;

        double x[] = new double[n];

        double y[] = new double[n];

        double low[] = new double[n];

        double high[] = new double[n];

        for (int k = 0;  k < n;  k++) {

            x[k] = k + 1;

            y[k] = r.nextDouble();

            low[k] = y[k] - 0.25*r.nextDouble();

            high[k] = y[k] + 0.25*r.nextDouble();

        }

       

        ErrorBar data = new ErrorBar(axis, x, y, low, high);

        data.setDataType(data.DATA_TYPE_ERROR_Y | data.DATA_TYPE_MARKER);

        data.setMarkerType(Data.MARKER_TYPE_FILLED_CIRCLE);

        data.setMarkerColor(Color.red);

    }

   

    public static void main(String argv[]) {

        new SampleErrorBar().setVisible(true);

    }

}

 

 

Horizontal Error Bars

It is also possible to have horizontal error bars, indicating errors in x, as shown in this example.

(Download Code)

 

import com.imsl.chart.*;

import java.awt.Color;

import com.imsl.stat.Random;

 

public class SampleHorizontalErrorBar extends JFrameChart {

 

    public SampleHorizontalErrorBar() {

        Random r = new Random(123457);

       

        Chart chart = getChart();

        AxisXY axis = new AxisXY(chart);

       

        // Generate a random data set, with random errors in x

        int n = 20;

        double x[] = new double[n];

        double y[] = new double[n];

        double low[] = new double[n];

        double high[] = new double[n];

        for (int k = 0;  k < n;  k++) {

            x[k] = k;

            y[k] = r.nextDouble();

            low[k] = x[k] - 5.*r.nextDouble();

            high[k] = x[k] + 5.*r.nextDouble();

        }

       

        ErrorBar data = new ErrorBar(axis, x, y, low, high);

        data.setDataType(

                ErrorBar.DATA_TYPE_ERROR_X | ChartNode.DATA_TYPE_MARKER);

        data.setMarkerType(Data.MARKER_TYPE_FILLED_CIRCLE);

        data.setMarkerColor(Color.red);

    }

   

    public static void main(String argv[]) {

        new SampleHorizontalErrorBar().setVisible(true);

    }

}

Mixed Error Bars

To show errors in both x and y, it is necessary to create both vertical and horizontal error bar objects. This example shows such a chart.

(Download Code)

 

import com.imsl.chart.*;

import java.awt.Color;

import com.imsl.stat.Random;

 

public class SampleMixedErrorBar extends JFrameChart {

 

    public SampleMixedErrorBar() {

        Random r = new Random(123457);

       

        Chart chart = getChart();

        AxisXY axis = new AxisXY(chart);

       

        // Generate a random data set, with random errors in x

        int n = 20;

        double x[] = new double[n];

        double y[] = new double[n];

        double xlow[] = new double[n];

        double xhigh[] = new double[n];

        double ylow[] = new double[n];

        double yhigh[] = new double[n];

        for (int k = 0;  k < n;  k++) {

            x[k] = k;

            y[k] = r.nextDouble();

            xlow[k] = x[k] - r.nextDouble();

            xhigh[k] = x[k] + r.nextDouble();

            ylow[k] = y[k] - 0.25*r.nextDouble();

            yhigh[k] = y[k] + 0.25*r.nextDouble();

        }

       

        ErrorBar dataY = new ErrorBar(axis, x, y, ylow, yhigh);

        dataY.setDataType(

                ErrorBar.DATA_TYPE_ERROR_Y | ChartNode.DATA_TYPE_MARKER);

        dataY.setMarkerType(Data.MARKER_TYPE_FILLED_CIRCLE);

        dataY.setMarkerColor(Color.red);

       

        ErrorBar dataX = new ErrorBar(axis, x, y, xlow, xhigh);

        dataX.setDataType(ErrorBar.DATA_TYPE_ERROR_X);

        dataX.setMarkerColor(Color.red);

    }

   

    public static void main(String argv[]) {

        new SampleMixedErrorBar().setVisible(true);

    }

}

 

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