core_question\statistics\questions\calculator Class Reference

This class has methods to compute the question statistics from the raw data. More...

Public Member Functions
	__construct ($questions, $progress=null)
	Constructor.
	calculate ($qubaids)
	Calculate the stats.
	get_cached ($qubaids)
	Load cached statistics from the database.
	get_last_calculated_time ($qubaids)
	Find time of non-expired statistics in the database.
	get_sum_of_mark_variance ()
	Used when computing Coefficient of Internal Consistency by quiz statistics.

Protected Member Functions
	get_latest_steps ($qubaids)
	Get the latest step data from the db, from which we will calculate stats.
	get_random_guess_score ($questiondata)
	Given the question data find the average grade that random guesses would get.
	initial_question_walker ($stats)
	Then loop through all questions for the first time.
	initial_steps_walker ($step, $stats, $summarks, $positionstat=true, $dovariantalso=true)
	Calculating the stats is a four step process.
	secondary_question_walker ($stats)
	And finally loop through all the questions again.
	secondary_steps_walker ($step, $stats, $summarks)
	Loop through all last step data again.

Protected Attributes
progress_trace	$progress
array[]	$randomselectors = array()
	keyed by a string representing the pool of questions that this random question draws from.
all_calculated_for_qubaid_condition	$stats
	all the stats calculated for slots and sub-questions and variants of those questions.
string	$statscollectionclassname = '\core_question\statistics\questions\all_calculated_for_qubaid_condition'
	The class name of the class to instantiate to store statistics calculated.
float	$sumofmarkvariance = 0

Detailed Description

This class has methods to compute the question statistics from the raw data.

Copyright

2013 Open University

Author

Jamie Pratt me@ja.nosp@m.miep.nosp@m..org

License

http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later

Constructor & Destructor Documentation

__construct()

core_question\statistics\questions\calculator::__construct	(		$questions,
			$progress = null )

Constructor.

Parameters

	object[]	questions to analyze, keyed by slot, also analyses sub questions for random questions. we expect some extra fields - slot, maxmark and number on the full question data objects.
core\progress\base | null	$progress	the element to send progress messages to, default is core\progress\none.

Member Function Documentation

calculate()

core_question\statistics\questions\calculator::calculate

(

$qubaids

)

Calculate the stats.

Parameters

qubaid_condition

$qubaids

Which question usages to calculate the stats for?

Return values

all_calculated_for_qubaid_condition

The calculated stats.

get_cached()

core_question\statistics\questions\calculator::get_cached

(

$qubaids

)

Load cached statistics from the database.

Parameters

qubaid_condition

$qubaids

Which question usages to load the cached stats for?

Return values

all_calculated_for_qubaid_condition

The cached stats.

get_last_calculated_time()

core_question\statistics\questions\calculator::get_last_calculated_time

(

$qubaids

)

Find time of non-expired statistics in the database.

Parameters

qubaid_condition

$qubaids

Which question usages to look for?

Return values

int|bool

Time of cached record that matches this qubaid_condition or false is non found.

get_latest_steps()

core_question\statistics\questions\calculator::get_latest_steps ( $qubaids )

protected

Get the latest step data from the db, from which we will calculate stats.

Parameters

qubaid_condition

$qubaids

Which question usages to get the latest steps for?

Return values

array

with two items $lateststeps array of latest step data for the question usages $summarks array of total marks for each usage, indexed by usage id

get_random_guess_score()

core_question\statistics\questions\calculator::get_random_guess_score ( $questiondata )

protected

Given the question data find the average grade that random guesses would get.

Parameters

object

$questiondata

the full question object.

Return values

float

the random guess score for this question.

get_sum_of_mark_variance()

core_question\statistics\questions\calculator::get_sum_of_mark_variance

(

)

Used when computing Coefficient of Internal Consistency by quiz statistics.

Return values

float

initial_question_walker()

core_question\statistics\questions\calculator::initial_question_walker ( $stats )

protected

Then loop through all questions for the first time.

Perform some computations on the per-question statistics calculations after we have been through all the step data.

Parameters

calculated

$stats

question stats to update.

initial_steps_walker()

core_question\statistics\questions\calculator::initial_steps_walker ( $step, $stats, $summarks, $positionstat = true, $dovariantalso = true )

protected

Calculating the stats is a four step process.

We loop through all 'last step' data first.

Update $stats->totalmarks, $stats->markarray, $stats->totalothermarks and $stats->othermarksarray to include another state.

Parameters

object	$step	the state to add to the statistics.
calculated	$stats	the question statistics we are accumulating.
array	$summarks	of the sum of marks for each question usage, indexed by question usage id
bool	$positionstat	whether this is a statistic of position of question.
bool	$dovariantalso	do we also want to do the same calculations for this variant?

secondary_question_walker()

core_question\statistics\questions\calculator::secondary_question_walker ( $stats )

protected

And finally loop through all the questions again.

Perform more per-question statistics calculations.

Parameters

calculated

$stats

question stats to update.

secondary_steps_walker()

core_question\statistics\questions\calculator::secondary_steps_walker ( $step, $stats, $summarks )

protected

Loop through all last step data again.

Now we know the averages, accumulate the date needed to compute the higher moments of the question scores.

Parameters

object	$step	the state to add to the statistics.
calculated	$stats	the question statistics we are accumulating.
float[]	$summarks	of the sum of marks for each question usage, indexed by question usage id

Member Data Documentation

$randomselectors

array [] core_question\statistics\questions\calculator::$randomselectors = array()

protected

keyed by a string representing the pool of questions that this random question draws from.

string as returned from core_question::statistics::questions::calculated::random_selector_string

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The documentation for this class was generated from the following file:

• question/classes/statistics/questions/calculator.php