[R] (no subject)

[Peter Flom]

Christophe Genolini <cgenolin at u-paris10.fr> wrote

>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 ? 
>

This is not my understanding of the terms.  To me, both time series
and longitudinal data can be regular or irregular, but time series data
typically have a lot more measurement points (20 at a minimum) and often
has only one or a few "subjects" - e.g. trends in the stock market.  Logitudinal
data are often collected at fewer time points, but with many subject
(e.g. measuring people repeatedly to see if something about them changes 
over time, and changes differently in different people).

Peter


Peter L. Flom, PhD
Statistical Consultant
www DOT peterflomconsulting DOT com