[[random_p()]]

`int `

**random_p**(array *distribution*)

Returns a number from the *distribution*. Each number can be assigned an individual probability in the process.

*distribution*

An array which specifies the possible numbers as keys, and their probability as a value. Therefore, each number is assigned a probability (number`=>`

probability). The probability can be specified as a percentage (e.g.`0.25`

), or as a relative proportion (e.g.`20`

).

**Note:** The distribution of the drawn values only converges once there have been many draws (n > 1000) of the distribution specified. If you are working with a lower number of cases, use randomization with urns, and enter some numbers more often in the urn, if these should be drawn more often.

**Note:** Use the function `put()`

to save the drawn value in the data record.

In the first example, a number between 1 and 4 is drawn. Numbers 1 and 3 each have a 20% chance of being drawn, number 2 has a 50% chance, and number 4 has a 10% chance. All three random numbers in the first example have the same random distribution.

// Define distribution $distribution = array( 1 => 20, 2 => 50, 3 => 20, 4 => 10 ); // Draw number between 1 and 4 $number = random_p($distribution); // Save the result of the random draw put('IV01_01', $number); // Show corresponding stimulus if ($number == 1) { text('stimulusA'); } elseif ($number == 2) { text('stimulusB'); } elseif ($number == 3) { text('stimulusC'); } else { text('stimulusD'); }

The probabilities can also be listed as floating-point numbers (with a point as the decimal separator). The numbers can be written directly one after the other as well.

// Probabilities as floating-point numbers $distribution = array(1=>0.2, 2=>0.5, 3=>0.2, 4=>0.1);

The probabilities do *not* have to add up to 1 or 100.

// Probabilities as ratios $distribution = array(1=>4, 2=>10, 3=>4, 4=>2);

And, of course, the distribution does *not* have to be saved separately in a variable.

// Draw number between 1 and 4 $number = random_p(array( 1 => 2, 2 => 5, 3 => 2, 4 => 1 ));

The second example demonstrates how a random selection can be made depending on the respondent's response.

The example assumes that in question “PS19”, how often 7 television stations were watched was requested, ranging from 1 (never), 2 (rarely), 3 (often) and 4 (almost daily).

One of the television stations watched at least rarely should now be selected at random. However, preference should be given to television stations 2, 5 and 6.

// Create a list in which all television stations watched appear $watched = getItems('PS19', 'min', 2); // If no station is watched, the survey is over if (count($watched) < 1) { goToPage('end'); } // Define probabilities for the various stations $pAll = array( 1 => 10, 2 => 20, 3 => 10, 4 => 10, 5 => 20, 6 => 30, 7 => 10 ); // A distribution must now be created for the stations watched $pWatched = array(); foreach ($watched as $station) { $pWatched[$station] = $pAll[$station]; } // Weighted random selection from the stations watched $focus = random_p($pWatched); // Store the subject matter put('PS20_01', $focus);