Length of the reference period
Subjective well-being questions often ask respondents to sum their experiences over a given reference period - such as emotions experienced yesterday, or satisfaction with life nowadays. Selection of the reference period ultimately needs to focus on the purpose of the measure (i.e. the underlying construct of interest) - and, particularly in the case of affect, the reference period plays a key part in defining what is being measured (because affect yesterday and affect last year are different things).
There are two central ways in which the reference period can influence the comparability of responses and the risk of error. The reference period provides information to respondents about the construct of interest (e.g. a measure of happiness experienced over one year might tap global life evaluations, whereas happiness experienced over one day is likely to capture more short-term affect). Second, if the reference period is too demanding - for example, if respondents are asked to recall over too long a time period - it may lead to misremembering and increase susceptibility to recall and response biases and context effects.
These issues raise two further questions. First, how similar do two reference periods need to be for measures to be considered comparable? And second, given the potential risks for error, what is the optimal reference period for each type of subjective well-being measure?