Growth Curves

 P50 = mean = mode = median = 2nd quantile

Mean + / – 1 × SD = 68.27 % :

between 16th and 84th percentile

Mean + / – 2 × SD = 95.45 % :

between 2nd and 98th percentile

Mean + / – 3 × SD = 99.73 % :

between 0.1th and 99.9 th percentile

Z-score = (height – mean height) / standard deviation

 

The Z-score is the number of standard deviations the

bone mineral density measurement is above or below

the age-matched mean bone mineral density.

Z-score = (BMD – age-matched mean BMD) / standard deviation

(BMD = bone mineral density)

 

The T-score is the number of standard deviations the

bone mineral density measurement is above or below

the young-normal mean bone mineral density.

T-score = (BMD – young-normal mean BMD) / standard deviation

(BMD = bone mineral density)

World Health Organisation definition (1994):

Normal:                           T-score -1 or above

Osteopenia:                    T-score between -1 and -2.5

Osteoporosis:                 T-score less than -2.5

Severe osteoporosis:   T-score less than -2.5 and fragility fracture