About the attribution "created_at" of Interactions.csv and items.csv

[LessEase]

We are confused with the attribute "created_at" in items.csv. What dose it mean? Why the description is the same as that of interactions.csv? Is't got wrong?

[dkohlsdorf]

Well it is the date the job got posted. The created at on an interaction is the time an interaction happened.

[lvfuyu]

Well, the week begins with 0 or 1 in the year? And one week begins with Monday or Sunday in this comp.

[creat89]

Why there are items with null values for "created_at"? Or what it means?