Adult Changes in Thought Study

The ACT Cohort

Study population and creation of the ACT cohort

The Adult Changes in Thought (ACT) Study recruits participants from random samples of Kaiser Permanente Washington (previously Group Health) health plan members who meet the following criteria:

  • At least 65 years of age
  • Do not have dementia
  • Do not reside in a nursing home
  • Enrolled in the health plan for at least 2 years
  • Primary health care clinic is in the greater Seattle area of King County

Since its inception in 1994, the ACT Study has recruited an Original Cohort (2,581 participants recruited from 1994 to 1996), an Expansion Cohort (811 participants recruited from 2000 to 2003), and a Replacement Cohort (2,371 participants recruited from 2004 to early 2020). The ongoing recruitment of new participants into the ACT Study as part of the Replacement Cohort was designed to maintain a study cohort of ~2,000 participants without dementia who were actively undergoing biennial follow-up. In 2020, recruitment of new participants was halted due to the COVID-19 pandemic and did not resume until late 2022. When recruitment resumed, the ACT Study initiated a new recruitment protocol with two goals: to increase representation of historically underrepresented groups within the ACT Study and to grow the active study cohort to ~3,000 participants. These efforts are ongoing.

As of the most recent data freeze (November 25, 2022), total cumulative enrollment ever in the ACT study was 5,763 people. Among those participants, the study had accrued 49,422 person-years of biennial follow-up data (mean 8.6, SD=6.1 years per person).  The active cohort of participants at risk for dementia outcomes as of that freeze data was 1,664 people.

Participant follow-up and study visit protocol

At ACT study intake (baseline) and then approximately every 2 years (biennially), ACT participants have in-person study visits at a research clinic or in the participants’ homes. At these visits, research staff members of the ACT Clinical Core collect participant information using a series of interview forms and measured tasks including a cognitive screening test. An abbreviated check-in telephone visit is offered if a participant is unable to attend an in-person biennial visit for any reason. In 2020, due to the COVID-19 pandemic, a new type of biennial visit was implemented (dubbed a ‘remote visit’). This type of visit is also conducted by telephone but, unlike the brief telephone visit, involves collection of many of the same forms as are procured at in-person visits. Remote visits continue to be an option in ACT, but their use has waned in favor of in-person visits since 2022.

If an ACT participant scores below a set threshold on the standard cognitive screening test at their biennial visit or if further cognitive evaluation is requested for other reasons, then the participant is referred for additional cognitive and neurological testing as part of a referral (diagnostic) visit. These referral visits are typically conducted in-person; however, due to the COVID-19 pandemic, a remote version of referral visits was implemented. Upon completion of diagnostic testing, a consensus committee convenes to determine whether to assign a dementia diagnosis to the participant. Participants continue on the biennial track until dementia, death, or study withdrawal.  

If a participant is assigned a dementia diagnosis through the consensus committee process, then they move to an annual study visit track. The annual study visit track has a separate study visit protocol and additional information collected via proxy (for example, family members, caregivers, etc.).

Information regarding the study forms collected at ACT visits and other domains of data available on ACT participants are described in the ACT Data Repository.​​​​​​​​

Key publications

The following publications provide additional detail on ACT Study design and the ACT cohort. These may be helpful supporting citations when publishing analyses using ACT data. 

  • Kukull WA, Higdon R, Bowen JD, McCormick WC, Teri L, Schellenberg GD, van Belle G, Jolley L, & Larson EB. (2002). Dementia and Alzheimer disease incidence: a prospective cohort study. Archives of Neurology, 59(11), 1737–1746. 
  • Larson EB, Wang L, Bowen JD, McCormick WC, Teri L, Crane P, & Kukull W. (2006). Exercise is associated with reduced risk for incident dementia among persons 65 years of age and older. Annals of Internal Medicine, 144(2), 73–81.  
  • Crane PK, Gibbons LE, McCurry SM, McCormick W, Bowen JD, Sonnen J, Keene CD, Grabowski T, Montine TJ, Larson EB. (2016). Importance of home study visit capacity in dementia studies. Alzheimer's & Dementia, 12(4):419-426.