quiz_statistics\calculator Class Reference

Class to calculate and also manage caching of quiz statistics. More...

Public Member Functions
	__construct (\core\progress\base $progress=null)
	calculate ($quizid, $whichattempts, core\dml\sql_join $groupstudentsjoins, $p, $sumofmarkvariance)
	Compute the quiz statistics.
	get_cached ($qubaids)
	Load cached statistics from the database.
	get_last_calculated_time ($qubaids)
	Find time of non-expired statistics in the database.

Static Public Member Functions
static	using_attempts_lang_string ($whichattempts)
	Given a particular quiz grading method return a lang string describing which attempts contribute to grade.
static	using_attempts_string_id ($whichattempts)
	Given a particular quiz grading method return a string id for use as a field name prefix in mdl_quiz_statistics or to fetch the appropriate language string describing which attempts contribute to grade.

Public Attributes
int const	TIME_TO_CACHE = 900
	previously, the time after which statistics are automatically recomputed.

Protected Member Functions
	attempt_counts_and_averages ($quizid, core\dml\sql_join $groupstudentsjoins)
	Calculating count and mean of marks for first and ALL attempts by students.
	median ($s, $fromqa, $whereqa, $qaparams)
	Median mark.
	sum_of_powers_of_difference_to_mean ($mean, $fromqa, $whereqa, $qaparams)
	Fetch the sum of squared, cubed and to the power 4 differences between sumgrade and it's mean.

Protected Attributes
core progress base	$progress

Detailed Description

Class to calculate and also manage caching of quiz statistics.

These quiz statistics calculations are described here :

http://docs.moodle.org/dev/Quiz_statistics_calculations#Test_statistics

Copyright

2013 The Open University

Author

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

License

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

Member Function Documentation

attempt_counts_and_averages()

quiz_statistics\calculator::attempt_counts_and_averages ( $quizid, core\dml\sql_join $groupstudentsjoins )

protected

Calculating count and mean of marks for first and ALL attempts by students.

See : http://docs.moodle.org/dev/Quiz_item_analysis_calculations_in_practise #Calculating_MEAN_of_grades_for_all_attempts_by_students

Parameters

int	$quizid
core\dml\sql_join	$groupstudentsjoins	Contains joins, wheres, params for students in this group.

Return values

stdClass

with properties with count and avg with prefixes firstattempts, highestattempts, etc.

calculate()

quiz_statistics\calculator::calculate	(		$quizid,
			$whichattempts,
		core\dml\sql_join	$groupstudentsjoins,
			$p,
			$sumofmarkvariance )

Compute the quiz statistics.

Parameters

int	$quizid	the quiz id.
int	$whichattempts	which attempts to use, represented internally as one of the constants as used in $quiz->grademethod ie. QUIZ_GRADEAVERAGE, QUIZ_GRADEHIGHEST, QUIZ_ATTEMPTLAST or QUIZ_ATTEMPTFIRST we calculate stats based on which attempts would affect the grade for each student.
core\dml\sql_join	$groupstudentsjoins	Contains joins, wheres, params for students in this group.
int	$p	number of positions (slots).
float	$sumofmarkvariance	sum of mark variance, calculated as part of question statistics

Return values

calculated\$quizstats

The statistics for overall attempt scores.

get_cached()

quiz_statistics\calculator::get_cached

(

$qubaids

)

Load cached statistics from the database.

Parameters

qubaid_condition

$qubaids

Return values

calculated|false

The statistics for overall attempt scores or false if not cached.

get_last_calculated_time()

quiz_statistics\calculator::get_last_calculated_time

(

$qubaids

)

Find time of non-expired statistics in the database.

Parameters

$qubaids

qubaid_condition

Return values

int|bool

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

median()

quiz_statistics\calculator::median ( $s, $fromqa, $whereqa, $qaparams )

protected

Median mark.

http://docs.moodle.org/dev/Quiz_statistics_calculations#Median_Score

Parameters

$s	integer count of attempts
$fromqa	string
$whereqa	string
$qaparams	string

Return values

float

sum_of_powers_of_difference_to_mean()

quiz_statistics\calculator::sum_of_powers_of_difference_to_mean ( $mean, $fromqa, $whereqa, $qaparams )

protected

Fetch the sum of squared, cubed and to the power 4 differences between sumgrade and it's mean.

Explanation here : http://docs.moodle.org/dev/Quiz_item_analysis_calculations_in_practise #Calculating_Standard_Deviation.2C_Skewness_and_Kurtosis_of_grades_for_all_attempts_by_students

Parameters

$mean
$fromqa
$whereqa
$qaparams

Return values

stdClass

with properties power2, power3, power4

using_attempts_lang_string()

static quiz_statistics\calculator::using_attempts_lang_string ( $whichattempts )

static

Given a particular quiz grading method return a lang string describing which attempts contribute to grade.

Note internally we use the grading method constants to represent which attempts we are calculating statistics for, each grading method corresponds to different attempts for each user.

Parameters

int

$whichattempts

which attempts to use, represented internally as one of the constants as used in $quiz->grademethod ie. QUIZ_GRADEAVERAGE, QUIZ_GRADEHIGHEST, QUIZ_ATTEMPTLAST or QUIZ_ATTEMPTFIRST we calculate stats based on which attempts would affect the grade for each student.

Return values

string

the appropriate lang string to describe this option.

using_attempts_string_id()

static quiz_statistics\calculator::using_attempts_string_id ( $whichattempts )

static

Given a particular quiz grading method return a string id for use as a field name prefix in mdl_quiz_statistics or to fetch the appropriate language string describing which attempts contribute to grade.

Note internally we use the grading method constants to represent which attempts we are calculating statistics for, each grading method corresponds to different attempts for each user.

Parameters

int

$whichattempts

which attempts to use, represented internally as one of the constants as used in $quiz->grademethod ie. QUIZ_GRADEAVERAGE, QUIZ_GRADEHIGHEST, QUIZ_ATTEMPTLAST or QUIZ_ATTEMPTFIRST we calculate stats based on which attempts would affect the grade for each student.

Return values

string

the string id for this option.

Member Data Documentation

TIME_TO_CACHE

int const quiz_statistics\calculator::TIME_TO_CACHE = 900

previously, the time after which statistics are automatically recomputed.

Deprecated

since Moodle 4.3. Use of pre-computed stats is no longer time-limited.

Todo

MDL-78091 Final deprecation in Moodle 4.7

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

• mod/quiz/report/statistics/classes/calculator.php