Two situations are explained below. Identify and explain whether each is a natural experiment or not.

i. We are interested in identifying the impact of the size of the police force on the number of robberies committed in Washington, DC. Two economists have noticed that the number of police in Washington, DC fluctuates with the terror alert level. The terror alert level represents how likely it is that a terrorist attack will happen.

ii. We are interested in identifying the impact of prenatal visits on infant health. An economist notices that there is a great deal of variation in the number of prenatal visits mothers attend due to the amount of insurance coverage they have. Mothers will tend to have better insurance when they are married, more educated, and working.