# Single point in time

From Demography

## Definition

The term **single point in time** or **snapshot** is used to refer to situations where we want to calculate measures, or ratios of measures, that involve counts of entities (typically, counts of living populations and subpopulations) at a *single point in time*. We cannot use *single point in time* to calculate counts of *events*, because events can only be measured in a given measurement period (typically a year).

## Ratios that make sense at a single point in time

Note that these ratios *must* have both their numerator and denominator as measuring counts of entities, typically, subpopulations of a given population.

Some examples are: