"A kyphosis angle >40° has been widely accepted as the threshold for hyperkyphosis, although no published consensus exists 5,7,9. Using the >40° threshold, the incidence of hyperkyphosis in 60-year-olds and over is ~30% (range 20-40%), and in 70-year-olds and over is ~55% 7. Thus, some authors recommend a threshold of >50° 5 or >60° 7 to avoid overdiagnosis, although an age-adjusted range between 20-60° may be more appropriate 7."
"has inter- and intra-observerser variation of 3-5° 5"