Growth of infants in Egypt. A study of nutrition in developing countries collected data from the Egyptian village of Nahya. Here are the mean weights (in kilograms) for 170 infants in Nahya who were weighed each month during their first year of life
(a) Plot weight against time.
(b) A hasty user of statistics enters the data into software and computes the least-squares line without plotting the data. The result is
The regression equation is weight = 4.88 + 0.267 age
Plot this line on your graph. Is it an acceptable summary of the overall pattern of growth? Remember that you can calculate the least-squares line for any set of two-variable data. It's up to you to decide if it makes sense to fit a line.
(c) Fortunately, the software also prints out the residuals from the least-squares line. In order of age along the rows, they are
Verify that the residuals have sum zero (except for roundoff error). Plot the residuals against age and add a horizontal line at zero. Describe carefully the pattern that you see.