* do-file for Supplementary Exercise 2.53
version 13 /* works also with version 14 */

import delimited "H:\VHM\VHM801\Datasets\csv\Chapter 2\ex02_053.csv"
scatter vein spheres
twoway (scatter vein spheres) (lfit vein spheres)
regress vein spheres
* one method to obtain predictions for x-values not in the dataset 
* is to insert new observations (leaving the y-value as missing)
* either using the edit window, or using commands like the following:
set obs 13
replace spheres=6 in 11
replace spheres=12 in 12
replace spheres=18 in 13
* now, the prediction is done in the same way as before
predict fit, xb
predict pe_fit, stdf
scalar tstar=invttail(8,.025)
generate pe_low=fit-tstar*pe_fit
generate pe_upp=fit+tstar*pe_fit
list in 11/13, separator(5)