Dropouts and refusals in observational studies
Lessons for prevention trials
Citation Manager Formats
Make Comment
See Comments

This article requires a subscription to view the full text. If you have a subscription you may use the login form below to view the article. Access to this article can also be purchased.
Abstract
The success of prevention trials of Alzheimer disease and other dementias (AD/dementia) hinges on their ability to recruit and retain at-risk study populations. Losing subjects is a threat to the power to detect a treatment effect and, potentially, to the validity of these studies. Observational cohort studies accumulate data around participant outcomes that can help to inform the design of future prevention trials. Our objectives were to investigate the rates of refusal and dropout within observational cohort studies and to evaluate their characteristics and impact. This study examined data from the Canadian Cohort Study of Cognitive Impairment and Related Dementias (ACCORD), a 2-year observational cohort study of patients newly referred to dementia clinics. The sample included 124 Not Cognitively Impaired (NCI) and 342 Cognitively Impaired Not Demented (CIND) subjects. Subjects who refused initial neuropsychological (NP) testing were compared to those who completed NP testing and subjects who dropped out to those who attended follow-up. Refusal was common, with 40% of subjects not completing neuropsychological testing at baseline. Dropout was also substantial, with 55% lost to the 2-year follow-up. Subjects who refused NP testing were significantly older and less educated. CIND refusers had lower cognitive and functional scores at entry and a 2-year progression rate to dementia twice as high as that of non-refusers. CIND dropouts also had lower baseline cognitive and functional scores. These observations suggest that dropouts and refusals in prevention trials include those subjects who are at high risk for progression to AD/dementia. Targeted strategies to retain these individuals within prevention studies will be needed to achieve sufficient study power and validity.
AAN Members
We have changed the login procedure to improve access between AAN.com and the Neurology journals. If you are experiencing issues, please log out of AAN.com and clear history and cookies. (For instructions by browser, please click the instruction pages below). After clearing, choose preferred Journal and select login for AAN Members. You will be redirected to a login page where you can log in with your AAN ID number and password. When you are returned to the Journal, your name should appear at the top right of the page.
AAN Non-Member Subscribers
Purchase access
For assistance, please contact:
AAN Members (800) 879-1960 or (612) 928-6000 (International)
Non-AAN Member subscribers (800) 638-3030 or (301) 223-2300 option 3, select 1 (international)
Sign Up
Information on how to subscribe to Neurology and Neurology: Clinical Practice can be found here
Purchase
Individual access to articles is available through the Add to Cart option on the article page. Access for 1 day (from the computer you are currently using) is US$ 39.00. Pay-per-view content is for the use of the payee only, and content may not be further distributed by print or electronic means. The payee may view, download, and/or print the article for his/her personal, scholarly, research, and educational use. Distributing copies (electronic or otherwise) of the article is not allowed.
Letters: Rapid online correspondence
REQUIREMENTS
You must ensure that your Disclosures have been updated within the previous six months. Please go to our Submission Site to add or update your Disclosure information.
Your co-authors must send a completed Publishing Agreement Form to Neurology Staff (not necessary for the lead/corresponding author as the form below will suffice) before you upload your comment.
If you are responding to a comment that was written about an article you originally authored:
You (and co-authors) do not need to fill out forms or check disclosures as author forms are still valid
and apply to letter.
Submission specifications:
- Submissions must be < 200 words with < 5 references. Reference 1 must be the article on which you are commenting.
- Submissions should not have more than 5 authors. (Exception: original author replies can include all original authors of the article)
- Submit only on articles published within 6 months of issue date.
- Do not be redundant. Read any comments already posted on the article prior to submission.
- Submitted comments are subject to editing and editor review prior to posting.
You May Also be Interested in
Hastening the Diagnosis of Amyotrophic Lateral Sclerosis
Dr. Brian Callaghan and Dr. Kellen Quigg
► Watch
Related Articles
- No related articles found.
Alert Me
Recommended articles
-
Articles
Neuropsychological tests accurately predict incident Alzheimer disease after 5 and 10 yearsMary C. Tierney, Christie Yao, Alex Kiss et al.Neurology, June 13, 2005 -
Articles
Characterizing neuropsychiatric symptoms in subjects referred to dementia clinicsK. R. Peters, K. Rockwood, S. E. Black et al.Neurology, February 27, 2006 -
Articles
No advantage of Aβ42-lowering NSAIDs for prevention of Alzheimer dementia in six pooled cohort studiesC. A. Szekely, R. C. Green, J.C.S. Breitner et al.Neurology, May 28, 2008 -
Articles
Joint effect of stroke and APOE 4 on dementia riskThe Canadian Study of Health and AgingY. P. Jin, T. Østbye, J. W. Feightner et al.Neurology, October 31, 2007