Bibliography (5):

1. Maternal Mortality in the United States: Recent Trends, Current Status, and Future Considerations

2. Factors Underlying the Temporal Increase in Maternal Mortality in the United States

3. Infant and child death in the human environment of evolutionary adaptation

4. How the next recession could save lives: Death rates have dropped during past economic downturns, even as many health trends have worsened. Researchers are scrambling to decipher lessons before the next big recession

5. Wikipedia Bibliography:

   1. Confidence interval