Study on Incentives for Glaucoma Medication Adherence (SIGMA): study protocol for a randomized controlled trial to increase glaucoma medication adherence using value pricing.

Journal Article (Multicenter Study;Journal Article)


Many glaucoma patients do not adhere to their medication regimens because they fail to internalize the (health) costs of non-adherence, which may not occur until years or decades later. Behavioural economic theory suggests that adherence rates can be improved by offering patients a near-term benefit. Our proposed strategy is to offer adherence-contingent rebates on medication and check-up costs. This form of value pricing (VP) ensures that rebates are granted only to those most likely to benefit. Moreover, by leveraging loss aversion, rebates are expected to generate a stronger behavioural response than equivalent financial rewards.


The main objective of the Study on Incentives for Glaucoma Medication Adherence (SIGMA) is to test the VP approach relative to usual care (UC) in improving medication adherence. SIGMA is a randomized, controlled, open-label, single-centre superiority trial with two parallel arms. A total of 100 non-adherent (Morisky Medication Adherence Scale ≤6) glaucoma patients from the Singapore National Eye Centre are block-randomized (blocking factor: single versus multiple medications users) into the VP and UC arms in a 1:1 ratio. The treatment received by VP patients will be strictly identical to that received by UC patients, with the only exception being that VP patients can earn either a 50 % or 25 % rebate on their glaucoma-related healthcare costs conditional on being adherent on at least 90 % or 75 % of days as measured by a medication event monitoring system. Masking the arm allocation will be precluded by the behavioural nature of the intervention but blocking size will not be disclosed to protect concealment. The primary outcome is the mean change from baseline in percentage of adherent days at month 6. A day will be counted as adherent when the patients take all their medication(s) within the appropriate dosing windows.


This trial will provide evidence on whether adherence-contingent rebates can improve medication adherence among non-adherent glaucoma patients, and more generally whether this approach represents a promising strategy to cost-effectively improve chronic disease management.

Trial registration

NCT02271269 . Registered on 19 October 2014.

Full Text

Duke Authors

Cited Authors

  • Bilger, M; Wong, TT; Howard, KL; Lee, JY; Toh, AN; John, G; Lamoureux, EL; Finkelstein, EA

Published Date

  • July 15, 2016

Published In

Volume / Issue

  • 17 / 1

Start / End Page

  • 316 -

PubMed ID

  • 27422389

Pubmed Central ID

  • PMC4947326

Electronic International Standard Serial Number (EISSN)

  • 1745-6215

International Standard Serial Number (ISSN)

  • 1745-6215

Digital Object Identifier (DOI)

  • 10.1186/s13063-016-1459-1


  • eng