int random_p(array distribution)
Returns a number from the distribution. Each number can be assigned an individual probability in the process.
=> 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);