run meridian using monthly data

[marwawer1]

Hi,

I wanted to run Meridian using monthly data, but due to the interval days check, it requires equal intervals between observations, which is inconvenient for monthly data. Is there a way to modify this requirement for monthly data so that we can, for example, prepare data for the first day of each month? I believe this error might occur quite often,
so it might be beneficial to work on a general solution.

Please see below interval_days() method in https://github.com/google/meridian/tree/main/meridian/data/time_coordinates.py

@functools.cached_property
def interval_days(self) -> int:
"""Returns the interval between two neighboring dates in all_dates.

Raises:
  ValueError if the date index is not regularly spaced.
"""
# Calculate the difference between consecutive dates, in days.
diff = self.datetime_index.to_series().diff().dt.days.dropna()

if diff.nunique() == 0:
  # This edge case happens when there is only one date in the index.
  # This is unlikely to happen in practice, but we handle it just in case.
  warnings.warn(
      "The time coordinates only have one date. Returning an interval of 0."
  )
  return 0

Please see below the error I encountered when I tried to run Meridian using monthly data with observations on the first day of each month.

Best Regards,
Marlena

[cpulavarthi]

Hello Marlena,

Thank you for highlighting the issues you are facing with the interval days check. We recommend using equally spaced 30 day intervals for monthly data.

We will take your feedback into consideration and check if it is feasible to modify and implement this in Meridian. You can track the previous changes to Meridian and unreleased feature updates in our Change Log.

Feel free to reach out for any further queries or suggestions regarding Meridian!

Google Meridian Support Team