ていか低下teika
1.
The process of decreasing in degree or level, resulting in a lower state compared to a previous point.
2.
The deterioration of quality or capability, where standards or effectiveness become poorer or less desirable.
3.
The action of moving towards a lower position or status, manifesting in areas such as health, performance, or condition.
Example:
たしかに出生率の低下で子供の数が減り、学校でも生徒の数が少なくなっているのは事実ですが、しかし、これはまったくもってけっこうなことです。