Thus, a woman's fertility begins to decline significantly after the age of 35. Spontaneous and successful pregnancies after the age of 40 become less common, and after the age of 45 are rare (but not zero!). The woman seeking natural conception at this age will find that the facts are fairly discouraging. While 80% of women between 40 and 45 can potentially conceive with different methods, this percentage falls off dramatically after the age of 45. The average woman notices that by this time her cycle is already less regular.
An externality is a consequence of an economic activity experienced by unrelated third parties; it can be either positive or negative. Pollution emitted by a factory that spoils the surrounding environment and affects the health of nearby residents is an example of a negative externality.
When negative externalities are present, it means that the producer does not bear all costs, resulting in excess production. With positive externalities, the buyer does not get all the benefits of the good, resulting in decreased production. An example of a negative externality is a factory that produces widgets but pollutes the environment in the process. The cost of the pollution is not borne by the factory but instead shared by society.