What does infant mortality rate refer to?
1. The ratio of the number of children who die before their fifth birthday out of every 1000 live births.
2. The ratio of the number of children who die before their first birthday out of every 1000 live births.
3. The ratio of the number of children who die before their fifth birthday out of every 100 live births.
4. The ratio of the number of children who die before their first birthday out of every 100 live births.