org.statcato.statistics.inferential
Class CI2PopMeanSigmaUnknown

java.lang.Object
  extended by org.statcato.statistics.inferential.ConfidenceInterval
      extended by org.statcato.statistics.inferential.CI2PopMeanSigmaUnknown

public class CI2PopMeanSigmaUnknown
extends ConfidenceInterval

Confidence interval class for two population mean, sigma (population standard deviation) unknown.

Since:
1.0
Version:
%I%, %G%
Author:
Margaret Yau

Field Summary
 
Fields inherited from class org.statcato.statistics.inferential.ConfidenceInterval
center, confidenceLevel
 
Constructor Summary
CI2PopMeanSigmaUnknown(double confidenceLevel, int n1, int n2, double xBar1, double xBar2, double s1, double s2, boolean varEqual)
          Constructor
 
Method Summary
 double criticalValue()
          Returns the critical value corresponding to the given confidence level.
 int DOF()
          Returns the degrees of freedom.
 double marginOfError()
          Returns the margin of error.
 
Methods inherited from class org.statcato.statistics.inferential.ConfidenceInterval
center, lowerLimit, toString, upperLimit
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Constructor Detail

CI2PopMeanSigmaUnknown

public CI2PopMeanSigmaUnknown(double confidenceLevel,
                              int n1,
                              int n2,
                              double xBar1,
                              double xBar2,
                              double s1,
                              double s2,
                              boolean varEqual)
Constructor

Parameters:
confidenceLevel - confidence level, between 0 and 1
n1 - sample size 1
n2 - sample size 2
xBar1 - sample mean 1
xBar2 - sample mean 2
s1 - sample standard deviation 1
s2 - sample standard deviation 2
varEqual - whether the population variances are assumed to be equal
Method Detail

marginOfError

public double marginOfError()
Returns the margin of error. If population variances are assumed equal, E = t_(alpha/2) * sqrt(sp^2 / n1 + sp^2 / n2), where sp^2 = [(n1 - 1)*s1^2 + (n2 - 1)*s2^2] / [n1 + n2 - 2] If population variances are not assumed equal, E = t_(alpha/2) * sqrt(s1^2 / n1 + s2^2 / n2)

Specified by:
marginOfError in class ConfidenceInterval
Returns:
margin of error

criticalValue

public double criticalValue()
Returns the critical value corresponding to the given confidence level. Uses Student's t distribution to find t_(alpha/2), where alpha is the significance level (1 - confidence level).

Specified by:
criticalValue in class ConfidenceInterval
Returns:
critical value

DOF

public int DOF()
Returns the degrees of freedom.

Returns:
degrees of freedom