Cataracts Facts. 1  Cataracts are changes in clarity of the natural lens inside the eye that gradually degrade visual quality. The natural lens sits behind the colored part of the eye (iris) in the area of the pupil, and cannot be directly seen with the naked eye unless it becomes extremely cloudy.
Hershey and Chase. Alfred Hershey and Martha Chase did an Experiment in 1952 that was called the Hershey-Chase Experiment. This experiment set out to determine what composed the genetic material of a bacteriophage. A bacteriophage is a virus that infects a bacterium.
A quasi-experimental design is one that looks a bit like an experimental design but lacks the key ingredient -- random assignment. My mentor, Don Campbell, often referred to them as queasy experiments because they give the experimental purists a queasy feeling. With respect to internal validity, they often appear to be inferior to randomized experiments.