Table 1

Comparison of the three cohort types

	Cohort A	Cohort B	Cohort C
Purpose	To investigate incidence by comparing treated and untreated individuals.	To investigate incidence by comparing the different drug subclasses of each treatment.	To investigate progression by comparing treated and untreated individuals.
Number of cohorts required	There will be three cohorts of this type, one for each treatment of interest.	There will be three cohorts of this type, one for each treatment of interest.	There will be three cohorts of this type, one for each of dementia (AD or NADD), PD and ALS.
Exposures	Treatments for hypertension, hypercholesterolaemia and type 2 diabetes.	Treatments for hypertension, hypercholesterolaemia and type 2 diabetes.	Treatments for hypertension, hypercholesterolaemia, and type 2 diabetes.
Start of follow-up (index date)	Date at first risk of the condition the treatment is used for or date of first diagnosis of the condition itself if there was no preceding period ‘at risk’.	Date of first prescription of a treatment of interest.	Date of first diagnosis of neurodegenerative disease of interest.
Outcome	Diagnosis of neurodegenerative disease of interest.	Diagnosis of neurodegenerative disease of interest.	Death.
Exclusion criteria	Individuals with <12 consecutive months of records prior to cohort entry.	Individuals prescribed treatment and control medications at the same time or with <12 consecutive months of records prior to cohort entry.	Individuals with <12 consecutive months of records prior to cohort entry.
Statistical analysis	Conventional regression, propensity score regression, instrumental variable analysis and marginal structural models.	Conventional regression, propensity score regression, instrumental variable analysis and marginal structural models.	Conventional regression, propensity score regression and marginal structural models.

AD, Alzheimer's disease; ALS, amyotrophic lateral sclerosis; NADD, Non-Alzheimer's disease dementias; PD, Parkinson's disease.