This is a bar chart of the number of defaults on mortgages in a collection of loans during the credit crisis that began in XXXXXXXXXXThe bar chart identifies the type of income documentation used when...

This is a bar chart of the number of defaults on mortgages in a collection of loans during the credit crisis that began in 2007-2008. The bar chart identifies the type of income documentation used when the mortgage was obtained. Be fore we test whether loans with full documentation are more risky than the others, what else do we need to know?