1. Researchers have found a negative correlation between women's education and fertility. Women's education can cause a decline in fertility through which channels? It is also possible that some third factor is affecting an increase in women's education and a decrease in women's fertility, what are they?
2. Explain the natural experiment Angrist and Lavy (1999) used to determine the effect of class size on students performance. Why can we interpret their result as a causal relationship.