A pragmatic behavior-based habit index for adherence to nebulized treatments among adults with cystic fibrosis

Abstract

Background: Habit, a psychological process that automatically generates urges to perform a behavior in associated settings, is potentially an important determinant of medication adherence. Habit is challenging to measure because, as a psychological construct, it cannot be directly observed. We describe a method of using routinely available objective adherence data from electronic data capture (EDC) to generate a behavior-based index of adherence habit and demonstrate how this index can be applied.

Methods to generate the habit index: Our proposed habit index is a "frequency in context" measure. It estimates habit as a multiplicative product of behavior frequency (generated from weekly percentage adherence) and context stability (inferred from time of nebulizer use). Although different timescales can be used, we chose to generate weekly habit scores since we believe that this is the most granular level at which context stability can be reasonably calculated.

An application of the habit index: A hallmark of habit is to predict future behavior, hence we used time series method to cross-correlate the habit index with nebulizer adherence in the subsequent week among 123 adults with cystic fibrosis (52, 42.3% female; median age 25 years) over a median duration of 153 weeks (IQR 74-198 weeks). The mean cross-correlation coefficient (R) between the habit index and subsequent adherence was 0.40 (95% CI 0.36-0.44). Adjusting for current adherence, the unstandardized regression coefficient (B) for the habit index was 0.30 (95% CI -1.04 to 1.65).

Conclusion: We have described a pragmatic method to infer "habit" from adherence data routinely captured with EDC and provided proof-of-principle evidence regarding the feasibility of this concept. The continuous stream of data from EDC allows the habit index to unobtrusively assess "habit" at various time points over prolonged periods, and hence the habit index may be applicable in habit formation studies.

Keywords: cystic fibrosis; habits; medication adherence; nebulizers and vaporizers.

Figure 1

An example to illustrate the calculation of SD as a measure of variability for the time of nebulizer use.

Figure 2

An example to illustrate the calculation of SD for time of use in someone using nebulizer over two sessions. Notes: ^aEvening times were transformed into morning times for accuracy of calculation, otherwise nebulizer taken after midnight may cause spuriously large SD depending on the software used. For example, in someone who uses nebuliser at 23:45, 23:55, 00:15 and 23:52, the difference between 00:15 and 23:55 could be miscalculated as 23 hours and 40 minutes (instead of 20 minutes) if the date was not taken into account. ^bAlthough this treatment was taken after midnight, it is still part of the evening session treatment for 11/01/2013. Abbreviation: NA, not available.

Figure 3

Illustrative habit index (generated from time of nebulizer use) and adherence time series graphs.