The reference period for each good or service refers to the duration of time over which the observation of spending on that good or service is made.

It is very costly in terms of quality to investigate variables such as spending over a prolonged period. For these reasons, reference periods are introduced.

Due to both the factor of fatigue and the factor of forgetfulness, this type of survey is associated with reference periods that mean, in general, households are not asked about all their expenses during the entire study period but rather during a shorter period, so that, by applying a temporal scaling factor, an estimate of household expenditure over the entire study period can be obtained.