In function names, we use C for the former and c for the latter.įunction isleapsecond() tells you, as you might have guessed, whether the time in question is a leap second or not. There is debate about the utility of leap seconds, so at Stata we bookkeep both, that is, time with and without leap seconds. Every year or so since 1972, a leap second is added to align our clocks with the slowdown of the earth's rotation. We generally trust that our clocks synchronize perfectly with the motion of the earth, but it does not always run like clockwork. So if you use datetimes from datediff_frac() in a survival model and use ages from age() as predictors in the model, they will be consistent. datediff_frac() and age() calculate differences in a compatible manner. Calculating date differences accurately can be important in survival models. Tells the precise number of months from the day of the first documented case of COVID-19 until today. display datediff_frac(td(17nov2019), today(), "month") If you would like to calculate the precise number of months, say, for long-term monthly rental billing, Stata will find out whether the years in consideration have 365 or 366 days, and whether months have 28, 29, 30, or 31 days, and calculate the difference, as precisely as it gets. Functions age_frac() and datediff_frac() find, with precise fractions, the age, and in general, the difference in dates in units of year, month, or day. Insurance companies may want to know the details of a person's age, with every decimal place in age translating into dollars. For example, if you tied the knot on July 31, 2000, you may save the day with the knowledge you have been married for 3,652 days on your 10th wedding anniversary. age() is a special case of datediff() in years. The function datediff() calculates differences between dates in general, rounded down to the nearest integer, in various time units: year, month, or day. We do not provide the option for leaplings to celebrate their birthdays only every four years, considering the terrible ramifications, like the cruel fate of leapling Frederic in the comic opera Pirates of Penzance, who had to wait 63 years to unite with his love on his "twenty-first birthday" ( Sullivan 1923). Note: td() is a function that conveniently makes Stata understand literal dates. For example, if you were born on the leap day of 2000, the following tells you that you are still 17 at the end of February 2018 because March 1 is your birthday in nonleap years. The function age() tells you the age, in integers, with an optional argument for handling leaplings. The renewal of driver's licenses or the penalty for prematurely hitting the bar will be determined accordingly. If you were born on February 29, you age up on March 1 in UK but on February 28 in Taiwan–in nonleap years, of course. What is the difference, say, in milliseconds, between two timestamps if leap seconds are counted, based on Coordinated Universal Time (UTC) standards?ĭatetime functions, in both Stata and Mata, accurately and conveniently handle datetimes for (1) calculating durations, such as age and other datetime differences (2) finding relative dates, such as the next birthday after a given date and (3) extracting components of Stata datetime values and variables. Sometimes, they can get tricky, and the quirks of calendars and clocks have to be dealt with.įor example, when do leaplings (persons born on February 29) celebrate their birthdays in nonleap years? And when is a year a leap year? It is not just every four years. They lurk under data management and statistical analysis (and the underlying computer system) with various degrees of importance depending on the task at hand. Functions that extract the different components from datetime values and variablesĭates and times (or datetimes) are all too familiar concepts we often take for granted.Functions that calculate relative dates, or dates from other dates, such as the previous or next birthday or anniversary relative to a given date.Functions that calculate durations, such as ages and other differences between datetimes.
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