/**
* Pearson's Chi-Squared Goodness of Fit Test
*
* Tests whether a set of observations is significantly different than a
* set of expected values. To test goodness of fit against a distribution,
* use the appropriate distribution class to generate a corresponding set
* of expected values before calling this.
*
* @param array $observations The set of observations to be tested
* @param array $expected The set of expected values to be tested
* @param int $df The degrees of freedom in the test
* @return float The probability of getting the chi-squared statistic or more, the p-value
*/
public function chiSquareTest(array $observations, array $expected, $df)
{
$sum = 0;
$pairsTested = min(count($observations), count($observations));
for ($i = 0; $i < $pairsTested; $i++) {
if ($expected[$i] == 0) {
continue;
}
$sum += pow($observations[$i] - $expected[$i], 2) / $expected[$i];
}
return $this->chi->getSf($sum, $df);
}
/**
* Returns the survival function, the probability of getting the test value or something above it
*
* @param float $x The test value
* @return float The probability
*/
public function sf($x)
{
return $this->calculator->getSf($x, $this->k);
}