I feel confused by when to lump categorical variables.
For this case, lump level 0 and level 1 should be fine because level 0 only has 1 patient.
This is another example,
Should I lump level 0 and level 1?
Actually, I am wondering whether there is a criteria/cut-off point to start the action of lumping different levels.
Thank you so much and wish you stay well!