php-ml/docs/math/statistic.md
2016-05-14 21:30:13 +02:00

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# Statistic
Selected statistical methods.
## Correlation
Correlation coefficients are used in statistics to measure how strong a relationship is between two variables. There are several types of correlation coefficient.
### Pearson correlation
Pearsons correlation or Pearson correlation is a correlation coefficient commonly used in linear regression.
Example:
```
use Phpml\Math\Statistic\Correlation;
$x = [43, 21, 25, 42, 57, 59];
$y = [99, 65, 79, 75, 87, 82];
Correlation::pearson($x, $y);
// return 0.549
```
## Mean
### Arithmetic
Example:
```
use Phpml\Math\Statistic\Mean;
Mean::arithmetic([2, 5];
// return 3.5
Mean::arithmetic([0.5, 0.5, 1.5, 2.5, 3.5];
// return 1.7
```
## Median
Example:
```
use Phpml\Math\Statistic\Mean;
Mean::median([5, 2, 6, 1, 3, 4]);
// return 3.5
Mean::median([5, 2, 6, 1, 3]);
// return 3
```
## Mode
Example:
```
use Phpml\Math\Statistic\Mean;
Mean::mode([5, 2, 6, 1, 3, 4, 6, 6, 5]);
// return 6
```
## Standard Deviation
Example:
```
use Phpml\Math\Statistic\StandardDeviation;
$population = [5, 6, 8, 9];
StandardDeviation::population($population)
// return 1.825
$population = [7100, 15500, 4400, 4400, 5900, 4600, 8800, 2000, 2750, 2550, 960, 1025];
StandardDeviation::population($population)
// return 4079
```