The research description uses a rule of 3's.
3hrs of unexplained crying
at least 3hrs/day in the 1st 3 months.By definition it is not due to illess or defect. Brazleton set standards in the 70's for nl crying frequency peaking @ 6wks. Often attributed to tummy pain there is no proof, though many get gassy if they cry that much. It often disappears as baby begins to roll over & entertain themself.