Alzheimer’s disease and other dementias (GBD 2021)

Abbreviations

Abbreviation	Definition	Note
AD	Alzheimer’s Disease
YLD	Years Lived with Disability
YLL	Years of Life Lost

Disease Overview

GBD 2021 Modeling Strategy

Restrictions

The following table describes any restrictions in GBD 2021 on the effects of this cause (such as being only fatal or only nonfatal), as well as restrictions on the ages and sexes to which the cause applies.

GBD 2021 Cause Restrictions

Restriction Type	Value	Notes
Male only	False
Female only	False
YLL only	False
YLD only	False
YLL age group start	40 to 44	age_group_id = 13
YLL age group end	95 plus	age_group_id = 235
YLD age group start	40 to 44	age_group_id = 13
YLD age group end	95 plus	age_group_id = 235

Vivarium Modeling Strategy

For Model 1 of the Alzheimer’s simulation, we will model Alzheimer’s disease as a simple SI model using GBD data for the cause “Alzheimer’s disease and other dementias” (cause ID 543).

Cause Model Diagram

State Definitions

State	State Name	Definition
S	Susceptible	Simulant does not have Alzheimer’s disease or another dementia
AD	Alzheimer’s Disease	Simulant has Alzheimer’s disease or another dementia

Transition Definitions

Transition	Transition Name	Definition
i_AD	Alzheimer’s Incidence	Incidence rate of Alzheimer’s disease and other dementias (incident cases per susceptible person-year)

Data Tables

All data values are defined for a specified year, location, age group, and sex.

The population_agg.nc file from the Future Health Scenarios (FHS) team is located in the following folder:

/mnt/share/forecasting/data/9/future/population/ 20240320_daly_capstone_resubmission_squeeze_soft_round_shifted_hiv_shocks_covid_all_who_reagg/

Data Sources

Variable	Definition	Source or value	Notes
prevalence_c543	Prevalence of Alzheimer’s disease and other dementias	como
deaths_c543	Deaths from Alzheimer’s disease and other dementias	codcorrect
population	Average population during specified year	get_population (if using standard GBD data), or loaded from population_agg.nc file provided by FHS Team (if using forecasted data)	Numerically equal to person-years. Often interpreted as population at year’s midpoint (which is approximately equal to person-years if we think the midpoint rule with a single rectangle gives a good estimate of the area under the population curve).
incidence_rate_c543	GBD’s “total population incidence rate” for Alzheimer’s disease and other dementias	como	Raw GBD value, different from “susceptible incidence rate” automatically calculated by Vivarium Inputs
csmr_c543	Cause-specific mortality rate for Alzheimer’s disease and other dementias	\(\frac{\text{deaths\_c543}}{(\text{population}) \cdot (\text{1 year})}\)	Calculated automatically by Vivarium Inputs
emr_c543	Excess mortality rate for Alzheimer’s disease and other dementias	\(\frac{\text{csmr\_c543}}{\text{prevalence\_c543}}\)	Calculated automatically by Vivarium Inputs
sequelae_c543	Sequelae of Alzheimer’s disease and other dementias	Set of 3 sequelae: s452, s453, s454	Obtained from gbd_mapping. Sequela names are “Mild,” “Moderate,” or “Severe Alzheimer’s disease and other dementias,” respectively.
\(\text{disability\_weight}_s\)	Disability weight of sequela \(s\)	YLD Appendix	For reference, the values are: s452: 0.069 (0.046-0.099) s453: 0.377 (0.252-0.508) s454: 0.449 (0.304-0.595)
\(\text{prevalence}_s\)	Prevalence of sequela \(s\)	como

The following two tables describe the data needed for the cause model drawn in the previous section in terms of the data values in the above table.

State Data

State	Measure	Value	Notes
S	prevalence	1 - prevalence_c543 (if modeling entire population including susceptible simulants), or 0 (if modeling only simulants with AD as described in the Alzheimer’s population model)	Used for initial population at start of simulation
S	birth prevalence	1	Used for simulants born into the simulation
S	excess mortality rate	0	Added onto mortality hazard for susceptible simulants
S	disability weight	0	Used to calculate YLDs
AD	prevalence	prevalence_c543 (if modeling entire population including susceptible simulants), or 1 (if modeling only simulants with AD as described in the Alzheimer’s population model)	Used for initial population at start of simulation
AD	birth prevalence	0	Used for simulants born into the simulation
AD	excess mortality rate	emr_c543	Added onto mortality hazard for simulants with AD
AD	disability weight	\(\sum\limits_{s\in \text{sequelae\_c543}} \text{disability\_weight}_s \cdot \text{prevalence}_s\)	Prevalence-weighted average disability weight over sequelae, computed automatically by Vivarium Inputs. Used to calculate YLDs.
ALL	cause specific mortality rate	csmr_c543	Subtracted from all-cause mortality hazard to get cause-deleted mortality hazard in all cause states

Transition Data

Transition	Source State	Sink State	Value	Notes
i_AD	S	AD	\(\frac{\text{incidence\_rate\_c543}}{\text{1 - prevalence\_c543}}\)	Compute susceptible population incidence rate from GBD’s “total population incidence rate.” Conversion is automatic when using the get_measure function in Vivarium Inputs.