How to code recurring measuring points in the raw data files

Question

Let's assume I have three measuring points in time.

• T1 is study starts
• T2 after one week
• T3 after two weeks at the end

Without making it to complexe lets also assume there is only one numerical value on each point. How do you code that in the raw data (e.g. a CSV-file) and why?

I see two possibilities.

1. Horizontal (per proband)

PERSON-ID;T1;T2;T3
A;3;5;9
B;1;2;2
C;5;14;32
...

2. Vertical (per measure point)

PERSON-ID;T-POINT;VALUE
A;T1;3
A;T2;5
A;T3;9
B;T1;1
...

Please feel free to add the correct terminology for what I am talking here about.