  In the 20th century the scientific search for extraterrestrial intelligence
began, and the Drake equation was proposed to estimate the number of
extraterrestrial species humanity could attempt to detect, N. This paper
discusses the need to update and standardize this equation. A new and more
accurate expression is deduced which contains the classic equation as a
particular case, and its advantages are discussed. A necessary condition is
also stated for its use in scientific contexts: if N is defined as the total
number of civilizations like ours then N = 1, given that we exist, and
consequently the working hypothesis of the SETI project can be expressed as
N>1. In this case, the Drake equation is being applied in a scientific way,
because it is trying to test a hypothesis based on evidence.
