Consider using actual periods extended from OpenFisca-Core

[nikhilwoodruff]

OpenFisca-Core only provides YEAR, MONTH and DAY periods, and all amounts in the FRS are weeklyised, so we've been using ETERNITY so far. It's not too much work to add additional periods in OpenFisca-Core, so if we did add the FRS periods, then we could make the API a lot more intuitive, and likely make analyses involving specific time periods, e.g. phase-in reforms, a lot easier and more accurate, as well as making the internal policy implementations a lot more readable, eliminating the need to internally weeklyise/yearlyise variables, e.g. income tax is calculated on yearlyised income and then weeklyised again - the taxes and benefits have many different payable time periods, e.g. most benefits pay weekly, some monthly, some are one-off and this would be respected by default if we used periods correctly. It would also fix #33 , because all variables would have the correct period metadata.

[MaxGhenis]

Cool, so would this involve a PR to openfisca-core? Looks like they added day a couple years ago (openfisca/openfisca-core#763), and there's more discussion of other periods in openfisca/openfisca-core#670.

[nikhilwoodruff]

I think so, though I'm not sure how OpenFisca would prefer this to be done. One potential problem caused by this is that for the DAY, WEEK and YEAR periods, you can specify a specific period (e.g. for MONTH, we can specify "2020-01", "2020-02", etc.) as well as the start date and length(e.g. for MONTH, we could write "month:2020-01-01", "month:2020-02-01"). Under the dd-mm-YYYY format, this second method wouldn't be possible for weeks or any other period, making them inconsistent from the rest of the periods. But I do think it would be worth it in OpenFisca-UK even if it isn't suitable for OpenFisca-Core to have WEEK, FOUR_WEEKS and maybe others.

[nikhilwoodruff]

Added some code in frs-tools that parses period codes: potentially opening up a way to de-weeklyise FRS figures if we decide to.

[nikhilwoodruff]

Closing as this is very old - we made the decision a while ago to use yearly periods.