A histogram of birth weight in 1603 babies.
The horizontal axis is labeled Birth weight (g) and numbered 1000, 2000, 3000, 4000, 5000. The vertical axis is labeled Relative frequency density and numbered 0.0000, 0.0002, 0.0004, 0.0006, 0.0008, 0.0010.
There are vertical bars of width 200 grammes starting at 2000 and finishing at 4800.
The distribution is symmetrical, with the bars at 3200 to 3400 and 3400 to 3600 being equally the tallest at about 0.00085.
A smooth curve is drawn over the bars, going close to the middle of the tops of most of them. It can be seen just above the axis at birth weight = 1600 grammes and starts to rise at 2000, rising more steeply until 2800 grammes, where the relative frequency density is just above 0.0004. It continues to rise less steeply until it curves over just before 3400 grammes, relative frequency density = about 0.00087, to begin to descend. The descending curve is the exact oposite of the rising curve, falling more steeply until birth weight = 3900 grammes then less and less steeply until it is just above the axis at 4700 grammes. It finally disappears at 5000 grammes.
This is the Normal distribution curve. It is symmetrical about a vertical line through its highest point.
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This page maintained by Martin Bland.
Last updated: 22 July, 2009.