A teacher believes that giving her students a practice quiz
every week will motivate them to study harder, leading to a greater
overall understanding of the course material. She tries this
technique for a year, and everyone in the class achieved a grade of
a least C. Is this an experiment or an observational study? (A) An
experiment, but with no reasonable conclusion possible about cause
and effect (B) An experiment, thus making cause and effect a
reasonable conclusion (C) An observational study, because there was
no use of a control group (D) An observational study, but a poorly
designed one because randomization was not used (E) An
observational study, and thus a reasonable conclusion of
association but not of cause and effect