A concern that users of EMA have expressed is the possibility of reactive arrangements. This is the potential for the use of diaries to affect the experience of the phenomenon being studied. Certainly, this is a reasonable concern given the additional and unusual attention that will be paid to whatever is being recorded in the diary. Nevertheless, several studies suggest that a moderate density of momentary reporting does not have a major impact on reporting, at least over a 2- to
3-week period (Cruise, Porter, Broderick, Kaell, & Stone, 1996). Recently, Stone and colleagues (Stone et al., 2003) examined the possibility that the use of an ED affects the level of pain being reported over a 2-week period, using random sampling schedules with densities of 3, 6, or 12 times per day. Consistent with prior studies, Stone et al. observed little evidence of a shift in pain over time or according to sampling density. This study also examined the possibility that momentary reporting alters the recall of weekly pain reports that stem from reactive arrangements, and this was tested with both between-person and within-person analyses. The study showed no evidence that momentary recording procedures altered recall of pain.
Clearly, EMA protocol can be quite burdensome and possibly annoying for participants unless considerable care is taken. Although there are no "rules" about what is too much, several factors need consideration, including the following:
1. the length of the diary interview (from under a minute to many minutes),
2. the daily sampling density (from once a day to 25 or more per day),
3. the duration of study (from a single day to many weeks), and
4. the characteristics of the participant sample (from healthy adolescents to chronically ill patients).
If the burden is too great or the annoyance too high, then attrition will likely increase and compliance with the recording will decrease, both serious threats to the internal validity of a study.
The reactivity study mentioned above (Stone et al., 2003) used a 2-minute diary on pain over a 14-day period with chronically ill pain patients and examined three sampling densities. Protocol compliance was extremely good (94%) and did not differ by sampling density group. At the end of the study, participants rated how they felt about being in the study. In brief, although there were some expected effects in perceived burden according to sampling density, even the 12-day group rated the burden as just above "slightly burdensome" and the same for the degree of interference with daily activi ties. Importantly, all groups said they were at least "moderately" sure that if offered, they would participate in another study like the one they had just completed. Although this was only a single study addressing the issue, it seems reasonable that EMA protocols can be well tolerated by patients.
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