Define variance and define standard deviation. What is the importance of variance in statistics?

POST 1:

Define variance and define standard deviation. What is the importance of variance in statistics?

 

POST 2:
What is the difference between interventional studies and observational studies?

Provide an example of a clinical trial in the nursing field that relates to interventional and observational studies.

Explain what makes your example an interventional study or an observational study.