Lincoln Population Analysis: Census Reconciliation

Summary

This note presents a detailed reconciliation of the Town of Lincoln’s local census and the 2020 Federal (decennial) census, including an analysis of the portion residing on the base at Hanscom. This is an edited version of an email I shared with residents in 2022.

Lincoln’s situation is unusual because a portion of its population resides on federal property at Hanscom Air Force Base. These residents live in base housing and receive local services from the federal government. For some analyses using census data, we have to distinguish between the Hanscom and non-Hanscom populations.

Town Census Baseline

The official town census numbers are:

The current census data is available from Valerie Fox, our Town Clerk.

Federal Census Reconciliation

These numbers can be independently verified using the 2020 Federal census at the block level.

Step 1: Identify Lincoln’s Census Tract

The Town of Lincoln corresponds to MA census tract 3603. The total 2020 Federal census population for this tract was 7,014 (including Hanscom).

Source: Census Bureau Interactive Map

Census Tract 3603

Step 2: Identify Hanscom Census Blocks

Within tract 3603, census blocks 5000–5027 fall within the Hanscom base limits, with the exception of blocks #5026 and #5005. (Blocks 5001, 5003, and 5004 may also be outside the base, but they have zero population, so it doesn’t affect the calculation.)

Source: Census Block-Level Map Viewer

Hanscom Census Blocks

Step 3: Download Block-Level Population Data

The 2020 census “P1” dataset provides block-level population data for tract 3603.

Source: Census Data Table (P1 Dataset)

Shared spreadsheet with calculations: Google Sheet

Step 4: Calculate Hanscom and Non-Hanscom Populations

Total the Hanscom blocks, exclude blocks #5005 and #5026, and subtract from the Lincoln total:

Federal Census Town Census Variance Variance %
Lincoln total 7,014 6,865
Blocks 5000–5027 1,449
Less: Block 5005 16
Less: Block 5026 0
Net Hanscom population 1,433 1,257
Lincoln, Non-Hanscom 5,581 5,608 27 0.48%

Conclusion

The town and Federal censuses reconcile within ~0.5%.

Footnotes

Some residents have cited population figures from CensusReporter.org that differ significantly from the above. There are several reasons for this discrepancy.

CensusReporter Is Not an Official Census Site

It was not possible to drill into block-level detail on that site to confirm precisely how the “place” of Hanscom AFB was geographically defined. There may be boundary definition issues.

ACS Uses Estimates, Not Counts

More fundamentally, CensusReporter uses American Community Survey (ACS) 5-year data, not the 2020 decennial census. ACS data are estimates based on responses from approximately 2 million households sampled annually, roughly 1 in every 65 households. Assuming even sampling, this would yield only about 30–40 annual survey samples for all of Lincoln, and roughly 10 per year for Hanscom alone, a very small number.

Compounding Error Bars

Virtually every statistic for Lincoln or Hanscom on CensusReporter is accompanied by the disclaimer:

"† Margin of error is at least 10 percent of the total value. Take care with this statistic."

When subtracting two statistics (Hanscom population from Lincoln total population), each with a significant error bar, and with unknown error correlation, the resulting difference carries an even larger worst-case error bar. This is likely an ACS-derived estimate ends up ~15% or more off from the actual census count.

Data Sources