Learn in the textbookPopulation and Sampling
DefinitionA survey that examines every element of the population without exception is called a complete survey (全数調査, also 悉皆調査).
ExplanationThe more targets there are, the greater the cost, time, and staff required, and the longer the results take. In some cases, such as tests that destroy the product being checked, examining everything would make the survey itself impossible. A complete survey is therefore chosen when the number of targets is limited or when an exact figure for the whole is essential.
AnalogyIt is like a stocktake where a shop counts every item one by one. Nothing is missed, but the more products there are, the longer the shop has to stay closed.
Memory hookIts other Japanese name, 悉皆調査, uses 悉, read "kotogotoku" and meaning "every last one."