Thanks for yours answers. So if I understand:
- Trajectories are continuous, the other are discrete.
- The difference between time series and longitudinal is that time
series are made at regular time whereas longitudinal are not ?
- Repeated measures are over a short period of time.
So if I measure the weight of my patient daily during one week, it will
be repeated measure ; if I measure it once a week during one year,
it will time series ; if I measure it once a week during one year but
with some "missing week", it will longitudinal data ?
Well I guess it is not as simple at that, but is it the idea ?
Christophe
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.
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