Case Study 1 — The 2021–23 Inflation in Millbrook: What Your Grocery Bill Actually Looked Like

National inflation statistics are averages. This case study zooms in on what inflation actually looked like for a typical Millbrook household — and shows why the national number both tells the truth and hides important variation.

The Millbrook household

Consider the Reyes household: Maria (the adjunct professor from Chapter 13, earning $38,000), her partner David (a maintenance worker at MSU, earning $42,000), and their two children (ages 8 and 11). Combined household income: $80,000 before taxes. After taxes and deductions: about $62,000 in take-home pay, or roughly $5,200/month.

Their approximate monthly budget in early 2021 (before the inflation surge):

What happened to prices (2021–2023)

Here's how the prices the Reyes household faced changed during the inflation surge:

The national headline CPI peaked at 9.1% YoY in June 2022. But the Reyes household's personal inflation rate was much higher — probably 12–15% — because the categories that rose fastest (food, gas, housing) are a larger share of their budget than of the average consumer's.

This is the budget-share effect from Chapter 4: low-income households spend a disproportionate share on necessities (food, gas, rent), which rose faster than luxuries and services. The CPI, which reflects the spending patterns of an average urban consumer, understated the inflation experienced by the Reyes household.

The dollar impact

Let's compute the monthly increase in the Reyes household's cost of living from early 2021 to the peak (mid-2022):

$476 per month. That's $5,712 per year — a 9.2% increase in the household's cost of living, which is close to the national CPI peak but distributed differently (more on food and gas, less on services).

For a household earning $62,000 after taxes, a $5,712 annual cost increase is significant. It's not catastrophic — the Reyes family didn't go hungry — but it meant: - Savings dropped from $350/month to near zero - The family ate out less (shifting spending from restaurants to groceries) - Maria picked up an additional freelance editing client to make up the gap - The children's clothing budget was cut - A planned summer vacation was canceled

When Maria's lease renewed in the fall of 2022, rent went up to $1,400 — adding another $200/month to the household's costs. At that point, the total cost-of-living increase was about $676/month, or $8,100/year.

What the national CPI missed about the Reyes household

1. The budget-share effect. The CPI weights categories by the average consumer's spending pattern. The average consumer spends about 14% on food and 3% on gasoline. The Reyes household spends about 14% on food (similar) but a higher share on gas (they commute by car; there's no public transit in Millbrook). The CPI understates their inflation because their budget is tilted toward high-inflation categories.

2. The housing lag. The CPI measures shelter costs using "owners' equivalent rent" (an estimated rent for homeowners) and "rent of primary residence." Both are lagged — they reflect lease renewals, not real-time asking rents. For the Reyes family, the rent increase didn't hit until the lease renewed (fall 2022), but the market rent had been rising since early 2021. The CPI understated the real-time rent inflation.

3. The quality-adjustment gap. Some of the food price increases reflected genuine quality changes (organic became more expensive relative to conventional; premium brands rose faster than store brands). The CPI's quality adjustments may have partially accounted for this — but the Reyes household was buying the same items at higher prices, not better items.

What happened when inflation fell

By 2024, inflation had fallen back toward 2%. But prices did not fall — they stopped rising as fast. The CPI stabilized at a level about 20% above its 2020 level. The Reyes household's cost of living stabilized at the higher level — they were paying 2024 prices, which were permanently higher than 2021 prices.

This is one of the most important things to understand about inflation: falling inflation does not mean falling prices. It means prices are rising more slowly. The damage from the 2021–23 surge was permanent in the sense that the price level did not return to its pre-surge path. Households like the Reyes family absorbed a permanent reduction in real purchasing power.

The partial offset: wages eventually rose too. David's MSU wage went from $42,000 to $46,000 over the same period (about 10% — roughly matching inflation). Maria's adjunct pay rose modestly. But the timing mismatch — prices rose first, wages caught up later — meant the household experienced a real income decline for about 18 months before wages adjusted.

Discussion questions

1. The Reyes household experienced about 12–15% personal inflation when the national CPI was 9.1%. Why the difference? Should the CPI be adjusted for different income groups?
2. "Inflation is falling — the economy is recovering." Why is this statement misleading for a household like the Reyes family?
3. The household absorbed the inflation by cutting savings, eating out less, and canceling a vacation. Are these "costs of inflation" that the standard analysis captures?
4. Maria picked up extra freelance work to cover the increased costs. How does the labor supply model from Chapter 21 explain this response?
5. Compute your own household's personal inflation rate for the 2021–23 period. (Estimate your budget shares, look up the CPI for each category, and compute the weighted average.) How does it compare to the national average?