what does blockid do?

[Pakeezah Saadat]

Hello stata users,

I am working on a propensity score analysis and using

pscore

to create it. One of the options there is

blockid

which is defined as "specifies the variable name for the block number of the estimated propensity score" by Becker and Ichino 2002.

I don't quite understand what it does. What's the optimal number of blocks for a dataset, if any? What happens when you exceed a certain threshold of blocks? Please guide me to appropriate resources, if possible.

Thanks.