Experience sampling method
The experience sampling method, also referred to as a daily diary method, is a research methodology that asks participants to stop at certain times and make notes of their experience in real time. The point is for them to record temporal things like feelings while in the moment (right then, not later; right there, not elsewhere). They can be given a journal with many identical pages. Each page can have a psychometric scale, open-ended questions, or anything else used to assess their condition in that place and time. The method was developed by Larson and Csikszentmihalyi.
There are different ways to signal participants when to take notes in their journal, like using preprogrammed stopwatches. An observer can have an identically programmed stopwatch, so the observer can record specific events as the participants are recording their feelings or other behaviors. It is best to avoid letting subjects know in advance when they will record their feelings, so they can't anticipate the event, and will just be "acting naturally" when they stop and take notes on their current condition.
Validity in these studies comes from repetition, so you can look for patterns, like participants reporting greater happiness right after meals. These correlations can then be tested by other means for cause and effect, since ESM just shows correlation.
iHabit was the first smartphone platform for ESM. It was developed in 2011 and used in a study published by PLOS One in 2013. The creators of iHabit released their second platform, the LifeData system, in 2015. Other early smartphone platforms for ESM include Ilumivu's, developed in 2012, MetricWire's, developed in 2013, and Movisens'. Several other commercial and open source systems are currently available to help researchers run ESM studies, including the free software BeepMe. Due to limitations of past ESM platforms, a new ESM platform Expimetrics  was recently developed in 2016 by social scientists for social scientists. Expimetrics is free to use for social science research.
- Larson, R., & Csikszentmihalyi, M. (1983). "The experience sampling method". New Directions for Methodology of Social and Behavioral Science, 15, 41-56.
- Hektner, J.M., Schmidt, J.A., Csikszentmihalyi, M. (Eds.). (2006). Experience Sampling Method: Measuring the Quality of Everyday Life. Sage Publications, Inc. ISBN 978-1-4129-2557-0
- Runyan, J. D., Steenbergh, T. A., Bainbridge, C., Daugherty, D. A., Oke, L., Fry, B. N. (2013, August). "A smartphone ecological momentary assessment/intervention "app" for collecting real-time data and promoting self-awareness". PLOS ONE, 8, DOI: 10.1371/journal.pone.0071325
- Conner, T. S. (2013, May). Experience sampling and ecological momentary assessment with mobile phones. Retrieved from http://www.otago.ac.nz/psychology/otago047475.pdf
- as available through, e.g., F-Droid catalogue