Below isone ofthe growth charts inthe WHO report. Each curve represents a z- score forthe head circumference measurements forboys aged 0 to60 months. Imagine plottinga boy'sage and head circumference. If the dotlanded onthe curve labeled -3, then thisboy's head circumference has a z-scoreof-3when compared toother children ofthe same age. Use thisgrowth chart toanswer the followingquestions.

1. Consider the distribution ofhead circumferences for2-year oldboys.
   • Whichisamorereasonableestimateofthemean:45cm,47.5cmor50cm?Howcanyoutellfromthechart?

• Which isa more reasonable estimateof the standard deviation: 1.3cm or5.1cm?Howcanyoutellfromthechart?

W N J O - NW Head Circumference (cm) 2 - 8 - 8 - 0 2 4 6 8 12 16 20 24 28 32 36 40 44 48 52 56 60 Age (months) Figure 9 WHO head circumference-for-age z-scores for boys from birth to 60 months