At 04:02 PM 6/5/2009, Christophe Genolini wrote:
Hi the list
Strictly speaking, this is not a "R" question, but I need the
information for the
creation of a package. My question is about vocabulary: What is the
difference between
"time series", "longitudinal data" and "trajectories"?
Sincerely
Christophe
"Longitudinal" data are measurements over long periods of time, often
at irregular periods, but consistent across subjects.
"Repeated measures" data are replicates at the same point in time, or
over a short period of time (e.g., laboratory experiments).
"Time series" typically have constant increments of time and
typically a stochastic character, although this term might be
considered all-encompassing for all measurements at different times.
"Trajectory" implies a continuous curve in time, as opposed to
discrete times. "Trajectory" also implies an underlying causal model,
as it is a term from kinematics.
I hope this helps.
================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS e-mail: r...@lcfltd.com
Least Cost Formulations, Ltd. URL: http://lcfltd.com/
824 Timberlake Drive Tel: 757-467-0954
Virginia Beach, VA 23464-3239 Fax: 757-467-2947
"Vere scire est per causas scire"
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