This question refers to a study to determine whether a 100 mg caffeine pill, taken each morning before class, can improve the performance of a typical student on a statistics exam. Suppose all students in a 8:30 a. m. section are given the caffeine pill and all students in a 9:30 a. m. section are not permitted to have any caffeine before class. Later their scores from the midterm are compared.

Is this a controlled experiment or an observational study?

Observational study

Explanation:

An observational study can be defined as the process of studying the cause and effect relationships between the two variables without actually manipulating the independent variable like that occur in the controlled experiment. In observational study no control specimen is used for the purpose of comparison with the changes.The treatment groups or variables are also random.

According to the given situation, the direct effect of caffeine on performance has been derived by providing a group with caffeine and not permitting the other before class. This is an example of observational study as no control of parameters has been set for example timing of class.

c. taught scientists many new things about the earth, but not other planets.

explanation: