I've run into a bit of a conundrum when comparing one and five year results for Table B25038 TENURE BY YEAR HOUSEHOLDER MOVED INTO UNIT.

I am comparing values for the City of Cambridge, Massachusetts after calculating the percentage of householders who moved into their units in the prior two years, the most recent category provided.

For the period 2017 through 2021 I found the following proportions using one year data starting with 2017: 44%, 31%, 44%, null (no table for 2020), and 45%.

From the 2017-2021 ACS the same table generates the value of 17% for the same category.

Comparing published values, the 2021 ACS reports that 23,719 householders moved into their unit since 2019 where as the 2017-21 five year ACS reports 8,192. Similar discrepancies exist for 2017, 2018, and 2019.

While I do not expect one year and five year ACS data to match or have a simple mathematical relationship to one another, the level of the discrepancy is unusual in my experience. Have others had similar observations?