sick simulation

results.json

{
    "percent_sick_if_tested_positive": 4.458833791853989,
    "percent_healthy_if_tested_positive": 48.80539325842697,
    "percent_sick_if_tested_negative": 0.0011333259793069787,
    "percent_healthy_if_tested_negative": 49.99971666368849,
    "percent_tested_positive_and_sick": 49.719416386083054,
    "percent_tested_positive_and_healthy": 1.9703818540227784,
    "percent_tested_negative_and_sick": 1.1037527593818985,
    "percent_tested_negative_and_healthy": 49.49240211146362,
    "total_population": 5408000,
    "total_tested": 5408000,
    "total_sick": 5376,
    "total_healthy": 5402624,
    "total_positive": 113908,
    "total_negative": 5294092,
    "positive_and_sick": 5316,
    "positive_and_healthy": 108592,
    "negative_and_healthy": 5294032,
    "negative_and_sick": 60
}

sick_simulation.php

<?php

declare(strict_types=1);
/*
0.1% i Norge har en sykdom. 
Positiv test (+): testen sier at du har sykdommen
2% får positiv test selv om de ikke er syke
99% får positiv test når de er syke. 

Du tester deg og får positiv test - hva er sannsynligheten for at du er syk?
*/
use function var_dump as d;
function returnTrueXPercentOfTheTime(float $percent): bool
{
    return random_int(0, 100000) <= ($percent * 1000);
}


function calculatePercent(float $a, float $b): float
{
    return 100 * ($a / ($a + $b));
}

$total_population = 5_408_000; // population of Norway
$total_tested = $total_population;
$total_positive = 0;
$total_negative = 0;
$positive_and_sick = 0;
$positive_and_healthy = 0;
$negative_and_healthy = 0;
$negative_and_sick = 0;
$total_sick = 0;
$total_healthy = 0;
for ($personId = 0; $personId < $total_population; ++$personId) {
    $is_sick = returnTrueXPercentOfTheTime(0.1);
    $tested_positive = returnTrueXPercentOfTheTime($is_sick ? 99 : 2);
    if ($is_sick) {
        ++$total_sick;
        if ($tested_positive) {
            ++$total_positive;
            ++$positive_and_sick;
        } else {
            ++$total_negative;
            ++$negative_and_sick;
        }
    } else { // !$is_sick
        ++$total_healthy;
        if ($tested_positive) {
            ++$total_positive;
            ++$positive_and_healthy;
        } else {
            ++$total_negative;
            ++$negative_and_healthy;
        }
    }
}
$percent_tested_positive_and_sick = calculatePercent($positive_and_sick, $total_sick);
$percent_tested_positive_and_healthy = calculatePercent($positive_and_healthy, $total_healthy);
$percent_tested_negative_and_sick = calculatePercent($negative_and_sick, $total_sick);
$percent_tested_negative_and_healthy = calculatePercent($negative_and_healthy, $total_healthy);

$percent_sick_if_tested_positive = calculatePercent($positive_and_sick, $total_positive);
$percent_healthy_if_tested_positive = calculatePercent($positive_and_healthy, $total_positive);
$percent_sick_if_tested_negative = calculatePercent($negative_and_sick, $total_negative);
$percent_healthy_if_tested_negative = calculatePercent($negative_and_healthy, $total_negative);

$data = [
    'percent_sick_if_tested_positive' => $percent_sick_if_tested_positive,
    'percent_healthy_if_tested_positive' => $percent_healthy_if_tested_positive,
    'percent_sick_if_tested_negative' => $percent_sick_if_tested_negative,
    'percent_healthy_if_tested_negative' => $percent_healthy_if_tested_negative,
    'percent_tested_positive_and_sick' => $percent_tested_positive_and_sick,
    'percent_tested_positive_and_healthy' => $percent_tested_positive_and_healthy,
    'percent_tested_negative_and_sick' => $percent_tested_negative_and_sick,
    'percent_tested_negative_and_healthy' => $percent_tested_negative_and_healthy,
    'total_population' => $total_population,
    'total_tested' => $total_tested,
    'total_sick' => $total_sick,
    'total_healthy' => $total_healthy,
    'total_positive' => $total_positive,
    'total_negative' => $total_negative,
    'positive_and_sick' => $positive_and_sick,
    'positive_and_healthy' => $positive_and_healthy,
    'negative_and_healthy' => $negative_and_healthy,
    'negative_and_sick' => $negative_and_sick,
];
$pretty = json_encode($data, JSON_PRETTY_PRINT);
echo $pretty;