extrapolate

Concise Oxford English Dictionary © 2008 Oxford University Press:
extrapolate /ɪkˈstrapəleɪt, ɛk-/

▶verb

• 1 extend the application of (a method or conclusion) to different or larger groups.

• 2 extend (a graph) by inferring unknown values from trends in the known data.

– derivatives
extrapolation noun,
extrapolative adjective,
extrapolator noun.

– origin C19: from extra- + a shortened form of interpolate.