valueMean()

float valueMean(string question)

float valueMean(string question, string|array items)

float valueMean(array variables)

Calculates the mean (average, expectation value) of the answer codes for all items in a question (e.g. a scale), or for a list of variables.

• question – ID of a question (as a string)
• items – A list (string or array) of items
• variables – A list (array) of variable IDs as stated in the Variables Overview

Note This works in the same way as valueSum() – the parameters are described in this chapter in detail with various examples.

In the following example, question “AB02” will be displayed if the mean in the scale “AB01” is at least 1.5.

$mean = valueMean('AB01');
if ($mean >= 1.5) {
  question('AB02');
}

The following PHP code calculates the mean of the items 2, 4, 6, 8 and 10 in question AB02.

valueMean('AB01', [2, 4, 6, 8, 10])

The following PHP code calculates the mean of the variables AB03_01, AB03_02, BB01_02 and BB01_04.

valueMean(['AB03_01', 'AB03_02', 'BB01_02', 'BB01_04'])

Whether a Array is defined in one line or over several lines is irrelevant for the function, but can improve clarity.

valueMean([
    'AB03_01', 'AB03_02',
    'BB01_02', 'BB01_04'
])

It is not possible to calculate a weighted average using “valueMean()”, but using a FOR loop and simple arithmetic operations such a weighted average can be easily calculated using PHP.

$weights = [
    'AB03_01' => 1.1,
    'AB03_02' => 1.4,
    'BB01_02' => 0.7,
    'BB01_04' => 0.8
];
$sumValue = 0;
$sumWeight = 0;
 
foreach ($weights as $varID => $weight) {
    $val = (float)value($varID);
    // Exclude missing data (≤0)
    if ($val > 0) {
        $sumValue+= $val * $weight;
        $sumWeight+= $weight;
    }
}
 
// Mean = sum divided by count
if ($sumWeight == 0) {
  $mean = -1;  // No data
} else {
  $mean = $sumValue / $sumWeight;
}