A study compared the rate of pneumonia before and after a vaccine was introduced. In the?study, annual hospitalization rates were estimated from any cause using a database. Average annual rates of?pneumonia-related hospitalizations before and after introduction of the vaccine were used to estimate annual declines in?pneumonia-related hospitalizations. The annual rate of?pneumonia-related hospitalizations among children of various age groups significantly declined relative to expected rates before introduction of the vaccine. Does this show that pneumonia vaccine caused the decrease in pneumonia that?occurred? Explain.

O A. The study shows that the vaccine caused the decrease in pneumonia. This is an observational study because the number of treatment groups isn't sufficiently large to control for all relevant factors aside from vaccination. O The study shows that the vaccine caused the decrease in pneumonia. This is a controlled experiment. The children not vaccinated represent the control group, and the children vaccinated represent the treatment group. Since the vaccine was administered on a sufficiently large scale, other possible biases are eliminated. O C. The study does not show that the vaccine caused the dec crease in pneumonia. This is an observational study because the children were not randomly assigned by the researchers. It is possible that confounding variables (other advances in medicine, for instance) would affect the rates of pneumonia O D. The study does not show that the vaccine caused the decrease in pneumonia. This is a controlled experiment. Children cannot choose to be vaccinated, so whether or not a child was vaccinated is random. Confounding factors would affect all children equally, so such biases are eliminated