* SHAZAM code downloaded from UCLA Econ 143 (CAMERON) WebSite: 
* HTML file called e143sh4.htm, and should have 
*  been downloaded as study.sha

* example of omitted variables bias:  study time and midterm grade
* midterm=percent score on midterm exam
* study=hours spent studying for midterm in week before exam
* gpa=proxy for quality of advance preparation for coursework

sample 1 13
read midterm study gpa
95 2 4.0
75 4 3.6
75 3 3.6
90 6 3.6
62 4 3.3
75 6 3.3
73 7 3.3
85 8 3.3
70 8 3.0
75 9 3.0
95 1 4.0
98 3 4.0
55 6 3.0