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Add calculation for sample size

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This commit is contained in:
Dennis Eichhorn 2020-01-23 18:49:10 +01:00
parent 59f43a6a87
commit 15936c3a1a
2 changed files with 47 additions and 2 deletions
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39
Math/Stochastic/Distribution/NormalDistribution.php
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@ -25,9 +25,11 @@ namespace phpOMS\Math\Stochastic\Distribution;
final class NormalDistribution
{
/**
* Chi square table.
* Normal table.
*
* @var array<int, array<string, float>>
* Z-Score.
*
* @var array<string, float>
* @since 1.0.0
*/
public const TABLE = [
@ -35,6 +37,39 @@ final class NormalDistribution
'0.85' => 1.44, '0.90' => 1.64, '0.95' => 1.96, '0.96' => 2.05, '0.97' => 2.17, '0.98' => 2.33, '0.99' => 2.58,
];
/**
* Calculate the sample size
*
* @param float $zScore Z-Score
* @param float $errorMargin Error margin
* @param int $populationSize Population size
* @param float $populationProportion Proportion of the population (percentage)
*
* @return float
*
* @since 1.0.0
*/
public static function getSampleSizeFromPopulation(float $zScore, float $errorMargin, int $populationSize, float $populationProportion) : float
{
return self::getSampleSizeFromInfinitePopulation($zScore, $errorMargin, $populationProportion) / (1 + $zScore ** 2 * $populationProportion * (1 - $populationProportion) / ($errorMargin ** 2 * $populationSize));
}
/**
* Calculate the sample size
*
* @param float $zScore Z-Score
* @param float $errorMargin Error margin
* @param float $populationProportion Proportion of the population (percentage)
*
* @return float
*
* @since 1.0.0
*/
public static function getSampleSizeFromInfinitePopulation(float $zScore, float $errorMargin, float $populationProportion) : float
{
return ($zScore ** 2) * $populationProportion * (1 - $populationProportion) / ($errorMargin ** 2);
}
/**
* Get probability density function.
*

10
tests/Math/Stochastic/Distribution/NormalDistributionTest.php
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@ -83,4 +83,14 @@ class NormalDistributionTest extends \PHPUnit\Framework\TestCase
self::assertEquals($sig, NormalDistribution::getStandardDeviation($sig));
}
public function testSampleSizeCalculation() : void
{
self::assertEqualsWithDelta(277.54, NormalDistribution::getSampleSizeFromPopulation(NormalDistribution::TABLE['0.95'], 0.05, 1000, 0.5), 0.01);
}
public function testSampleSizeInfiniteCalculation() : void
{
self::assertEqualsWithDelta(384.16, NormalDistribution::getSampleSizeFromInfinitePopulation(NormalDistribution::TABLE['0.95'], 0.05, 0.5), 0.01);
}
}