Partial date handling with Arezzo

For the comparisons isbefore and isafter between date questions D1 and D2, where partial dates are allowed, comparisons will only be made between the time units that appear in both dates. For example:

D1	D2	Comparison
dd/mm/yyyy	dd/mm/yyyy	Use existing full date comparison
dd/mm/yyyy	mm/yyyy	Compare yyyy values: if equal, compare mm values
dd/mm/yyyy	yyyy	Compare yyyy values only
mm/yyyy	dd/mm/yyyy	Compare yyyy values: if equal, compare mm values
mm/yyyy	mm/yyyy	Compare yyyy values: if equal, compare mm values
mm/yyyy	yyyy	Compare yyyy values only
yyyy	dd/mm/yyyy	Compare yyyy values only
yyyy	mm/yyyy	Compare yyyy values only
yyyy	yyyy	Compare yyyy values only

For consistency with isbefore and isafter, a partial date is equal to a full date if the given parts match, i.e. if

D1 = 15/3/2001

D2 = 3/2001

then the condition

D1 = D2

will be true. Study designers must bear this in mind when dealing with partial dates. For example, assume D1 and D2 are dates with format of dd/mm/yyyy, mm/yyyy or yyyy:

D1	D2	D1=D2	D1 isbefore D2	D1 isafter D2
15/3/2001	3/2001	True	False	False
15/3/2001	2001	True	False	False
15/3/2001	4/2001	False	True	False
15/3/2001	2004	False	True	False
15/3/2001	2000	False	False	True
8/2001	31/8/2001	True	False	False
8/2001	8/2001	True	False	False
8/2001	5/2001	False	False	True
8/2001	2001	True	False	False
8/2001	2002	False	True	False
2003	2003	True	False	False
2003	7/2003	True	False	False
2003	11/7/2003	True	False	False
2003	2004	False	True	False
2003	10/1999	False	False	True
2003	1/1/2005	False	True	False

The time_diff function returns elapsed time, in whole time units. (This is the correct function for calculating a person’s age). For dates D1 and D2, the calculation can only be done for the following time units:

D1	D2	Time Units
dd/mm/yyyy	dd/mm/yyyy	years, months, weeks, days
dd/mm/yyyy	mm/yyyy	years
dd/mm/yyyy	yyyy	-
mm/yyyy	dd/mm/yyyy	years
mm/yyyy	mm/yyyy	years, months
mm/yyyy	yyyy	-
yyyy	dd/mm/yyyy	-
yyyy	mm/yyyy	-
yyyy	yyyy	years

 

To be able to calculate an age from a partial DOB, use the full_date function as described in this topic.

The date_diff function returns an arithmetical calendar difference (without considering parts of units). For dates D1 and D2, the calculation can only be done for the following time units:

D1	D2	Time Units
dd/mm/yyyy	dd/mm/yyyy	years, months, weeks, days
dd/mm/yyyy	mm/yyyy	years, months
dd/mm/yyyy	yyyy	years
mm/yyyy	dd/mm/yyyy	years, months
mm/yyyy	mm/yyyy	years, months
mm/yyyy	yyyy	years
yyyy	dd/mm/yyyy	years
yyyy	mm/yyyy	years
yyyy	yyyy	years

Date additions and subtractions involve expressions such as the following:

• DOB + 3 months

• StartDate - 2 days

Additions and subtractions can only be done if the date contains the specified time unit, i.e.

Date Format	Acceptable Time Units
dd/mm/yyyy	years, months, weeks, days
mm/yyyy	years, months
yyyy	years

 

The result will be a full or partial date of the same sort as the original. In the following examples D is a partial date question with format dd/mm/yyyy:

D	Arezzo Expression	Result
20/3/2006	D + 5 days	25/3/2006
20/3/2006	D - 1 week	13/3/2006
3/2006	D + 8 days	-
3/2006	D - 2 weeks	-
3/2006	D - 2 months	1/2006
3/2006	D + 3 years	3/2009
2006	D - 2 months	-
2006	D - 10 years	1996

To specify an explicit partial date in an Arezzo expression, use the date function with 0 for a missing month or day. For example:

Arezzo Expression	Meaning
date( 2005, 12, 25 )	25th December 2005
date( 1962, 10, 0 )	October 1962
date( 1945, 0, 0 )	1945

 

If a time is specified, the day and month must not be 0.

The function is_partial_date returns true or false depending on whether the given date is partial (regardless of a question's format). A partial date format may optionally be given. Note that the first argument must always be a date question (not a text question), or a date expression.

• is_partial_date( Date ) - True if the given date is either mm/yyyy, yyyy/mm or yyyy.

• is_partial_date( Date, 'my' ) - True if the given date is a month and a year only.

• is_partial_date( Date, 'y' ) - True if the given date is a year only.

For example:

D	is_partial_date( D )	is_partial_date( D, 'my' )	is_partial_date( D, 'y' )
3/11/1990	False	False	False
11/1990	True	True	False
1990	True	False	True

The function full_date converts a partial date to a full date, using a specified day and month to fill in missing values.

full_date( Date, Day1, Day2, Month )

If Date is a full date, the function returns the original date.

If Date is month-year, the function returns a date with the original month and year, and the Day1 value.

If Date is year-only, the function returns a date with the original year, and the Day2 and Month values.

 

In the following table, assume D1 is a date question with format dd/mm/yyyy:

D1	full_date( D1, 15,  30, 6 )
11/12/2005	11/12/2005
12/2005	15/12/2005
2005	30/6/2005

For calculating a person’s age from a partial date of birth, the following expression might be used:

time_diff( years, full_date( DOB, 1, 15, 6 ), datenow )

The age will be calculated based on an assumed birthdate of the first of the month where the day is not known, or the 15th of June if only the year is known. However, different study designers can choose to use different defaults for an unknown day and month.

The Arezzo max and min functions work with dates, giving the latest and earliest of a set of dates. However, max and min do not work on sets of dates which include dates of differing partial formats. For max and min to return a correct result, the set of dates must be one of:

• all full dates

• all month and year

• all year only

For any other combinations, max and min will be unknown (and a question derivation based on either function will remain blank).

For example:

D1	D2	D3	max( [D1, D2,D3] )	min( [D1, D2,D3] )
11/12/2005	3/4/2006	19/10/2005	3/4/2006	19/10/2005
12/2005	4/2006	10/2005	4/2006	10/2005
2005	2006	2005	2006	2005
11/12/2005	4/2006	19/10/2005	-	-
2005	3/4/2006	19/10/2005	-	-
11/12/2005	2006	10/2005	-	-