Health Burden in Washtenaw County (Ann Arbor), Michigan: Age-Standardized DALY Methodology

Method generation v2 · CDC WONDER 2020–2022 · CDC PLACES 2024 · IHME GBD 2021 · US-2000 standard population · Sergey Soshnikov, MD PhD

This is a planning-grade decision-support estimate, not a peer-reviewed study or an official GBD/IHME county estimate. It is intended to help public-health planners, grant writers, and community stakeholders prioritize. Every input is a public dataset; every step is reproducible.

1. Overview

This analysis quantifies the disease burden of Washtenaw County (which contains Ann Arbor) as Disability-Adjusted Life Years (DALYs) across seven condition groups: cancer, cardiovascular disease, chronic lower respiratory disease (COPD), stroke, diabetes, substance-use disorder, and a mental-health group. A DALY is one lost year of healthy life; it is the sum of Years of Life Lost to premature death (YLL) and Years Lived with Disability (YLD).

It uses the v2 age-standardized method, an upgrade over the crude method used for this site's smaller rural counties. The three upgrades: (a) YLL is computed age-specifically from a GBD reference life table rather than against one fixed benchmark age; (b) rates are age-standardized to the US-2000 population so counties with very different age structures can be compared fairly; (c) substance-use and mental-health mortality are directly observed by age, because Washtenaw is large enough that these counts are not statistically suppressed.

2. Data sources

2.1 Mortality — CDC WONDER

Deaths by cause × ten-year age group, Washtenaw County (FIPS 26161), 2020–2022 pooled, from the CDC WONDER Underlying Cause of Death, 2018–2024, Single Race database. The five chronic causes are the aggregate 113-cause-list rows: malignant neoplasms (C00–C97), diseases of heart (I00–I09, I11, I13, I20–I51), chronic lower respiratory (J40–J47), cerebrovascular (I60–I69), and diabetes (E10–E14). Substance use is the sum of drug-induced and alcohol-induced causes; the mental-health mortality proxy is intentional self-harm/suicide (X60–X84).

2.2 Prevalence — CDC PLACES 2024

Age-adjusted adult prevalence for each condition from the CDC PLACES county dataset (Socrata swc5-untb), which also supplies the adult (18+) population denominator. PLACES has no substance-use measure (see §4).

2.3 Disability weights & reference life expectancy

Disability weights are the IHME GBD 2021 values, reused unchanged across all counties (they are population-independent). Age-specific remaining life expectancy for YLL comes from the GBD 2019 reference life table (the same standard IHME uses), interpolated to each age group's midpoint.

2.4 Population denominators — Census PEP via CDC WONDER

Population by county × age group is drawn from the CDC WONDER Single-Race Population Estimates 2020–2022 (the Census Bureau's Population Estimates Program — the same denominators CDC uses for official age-adjusted death rates). We sum 2020, 2021 and 2022 to obtain person-years matching the 3-year pooled deaths, then annualize. Five-year population bands are collapsed to the ten-year mortality bands.

2.5 Economic parameters

Michigan GDP per capita $62,000 (BEA) for the human-capital method; income-adjusted HHS value of a statistical life $10.5M for the VSL method. Comorbidity correction factor 0.949 (Gaussian-copula net-YLD correction), reused from the Isabella pipeline.

3. Methods

3.1 DALY framework

DALY = YLL + YLD, no age-weighting and no time discounting, following the WHO Global Health Estimates convention.

3.2 Age-specific YLL

For each cause i and ten-year age group a with midpoint age m_a:

YLL(i,a) = deaths(i,a) × RLE(m_a)

where RLE(m_a) is the remaining life expectancy at age m_a interpolated from the GBD 2019 reference table. Pooled deaths are annualized (÷3). This replaces the crude method's single fixed 89.1-year benchmark, so a death at 40 and a death at 80 correctly lose different amounts of life.

3.3 YLD

YLD(i) = prevalence_ageadj(i) × adult_pop × DW(i) × CF

Prevalence is the PLACES age-adjusted value; DW the IHME disability weight; CF the 0.949 comorbidity factor. For the mental-health group, prevalence is PLACES depression × 0.50 (remission adjustment). PLACES provides no age-specific prevalence, so YLD carries no age structure (see §4).

3.4 Age-standardization (US-2000)

The cross-county comparison metric is the age-standardized YLL rate: the age-specific YLL rate per 100,000 in each band, weighted by the US-2000 standard population.

ASR_YLL = Σ_a [ YLL(a) / pop(a) × 100000 ] × w2000(a)

Standard weights are normalized over the ten age bands present (the <1 band is folded into 1–4 to match the population banding, and weights re-sum to 1). Washtenaw's age-standardized YLL rate is 8,251 per 100,000.

3.5 Substance-use & mental-health mortality

Unlike small rural counties, Washtenaw's substance-use and suicide deaths are numerous enough to be reported by age rather than suppressed, so both are observed directly rather than modeled from proxies.

3.6 Suppression handling

CDC WONDER suppresses cell counts of 1–9. Suppressed chronic-disease cells at young ages (<45), where the true count is near zero, are imputed at 1; suppressed substance-use/suicide cells are imputed at the midpoint 5. A 0-to-9 sensitivity band brackets the choice; the swing on the county total is under ±2%.

3.7 Economic burden

Human-capital: DALYs × $62,000. VSL: annual deaths × $10.5M (mortality only). Both are planning-grade, not audited fiscal figures.

4. Limitations & comparability

Comparability with this site's rural counties. Washtenaw and Wayne use the v2 age-standardized method; Isabella, Clare, Midland and Gratiot use the earlier v1 crude method (fixed reference life expectancy; substance-use and mental-health mortality suppressed and excluded). Rates across the two groups are not directly comparable and must not be ranked against one another. Compare within a method group only, or see the dedicated Rural vs Urban page, which discusses the seam explicitly.

"Age-standardized" applies to YLL only. Because PLACES gives no age-specific prevalence, YLD is reported as a crude rate (8,351/100k) and shown separately rather than blended into a single "age-standardized DALY rate."
Substance-use YLD prevalence is indicative. With no PLACES SUD measure, the SUD disability component uses a Michigan-derived rate applied uniformly; it does not reflect local variation. SUD mortality (YLL) is directly observed.
SUD/suicide overlap. Drug-poisoning suicides (X60–X64) fall in both the substance-use and suicide categories, so the sum of those two causes' YLL is a modest upper bound.
Prevalence basis. An age-adjusted prevalence is multiplied by an actual adult count — a standard but internally mixed convention.
Geography. Mortality is county-resolution only; Ann Arbor is described as part of Washtenaw County.

5. Results summary

Condition	Deaths/yr	YLL	YLD	DALYs
Cancer	548	11,113	6,192	17,305
CVD (heart disease)	616	9,648	5,638	15,286
Substance use	133	5,417	6,723	12,140
Mental health	47	2,137	5,509	7,647
COPD	94	1,558	2,987	4,544
Stroke	157	1,992	2,338	4,331
Diabetes	40	805	1,322	2,126
Total	1,635	32,670	30,709	63,379

Age-standardized YLL rate 8,251/100k · crude YLD rate 8,351/100k · crude DALY rate 17,235/100k · population 367,730 (2020–22 average).

6. Reproducibility & verification

The pipeline (Python) parses the raw CDC WONDER exports, applies the formulas above, and writes a machine-readable results file. An independent agent re-parsed the raw death files and re-implemented the engine from scratch, reproducing all 56 cause × county × metric cells and every total to the integer. Two suppression-sensitivity runs (0 and 9) bracket the central estimate. Data vintages: CDC WONDER 2020–2022, CDC PLACES 2024, CDC Single-Race Population Estimates 2020–2022, IHME GBD 2021.