Physiology Class

Question

Newborn babies: A study conducted by the Center for Population Economics at the University of Chicago studied the birth weights of 710

 babies born in New York. The mean weight was 3060

 grams with a standard deviation of 898

 grams. Assume that birth weight data are approximately bell-shaped.

Answer 1

Hello,

In Biostats a bell shaped curve refers to data that is organized so that the mean (the average of all data points) is in the center. Standard deviation (SD) means how much the data will differ (deviate) from the mean. 1 SD captures 68% if the data, 2 SD capture 95% and 3 SD 99.7% of the data.

The standard deviation sets a range for where all data points would exist i.e. 10 boys with an mean height of 50 inches and a standard deviation of 2 means that: 68% of the boys will be in the range 50 inches plus/minus 2 inches i.e. 48 to 52 inches. similarly 98% of boys would be the mean (50 inches) plus/minus 2 SD ie 4 inches which means between 46 and 54 and 99.7 percent of the boys would be within 3 SD's ie 44 to 56 inches.

There are 710 babies born with a mean weight of 3060 grams with a standard deviation of 898 grams. This means 68% babies are 3060 grams plus or minus 1SD ie 898 grams which is 2162 to 3958 grams. 95% are 3060 plus or minus 2 SD or 2 x 898 (1796 grams) which is 1264 to 4856. Finally almost all babies 99.7% will come in the rage of 3060 grams plus or minus 3 SD or 3x 898 (2694 grams) which gives us a range of 366 to 5754.

The final range takes into account the extreme values which may be few but significantly alter the data set and mean, these are called outliers.