CHAPTER 7 – Coursework Example

External and Internal invalidity Internal and external invalidity are common phenomenon in controlled and uncontrolled experiments. In internal invalidity, a different input other than the ones in use in the experiment causes a change in the observation. The contamination that exists during the experiment prevents one from concluding that the variables in the experiment are responsible for the change observed in the outcome. On the other hand, external invalidity refers to the degree at which the observations that appear in one experiment cannot be a generalization of other similar circumstances that occur in other areas. External and internal invalidity prevent one from discussing the outcome of an experiment confidently.
One of the causes of internal invalidity is the use of invalid instruments in the experiment. Ones a procedure begins with an invalid instrument, it is difficult to have confidence in the outcome produced. The second factor is the investigator’s bias acts. For an experiment to be accurate, the investigator needs to eliminate any form of biasness that may occur during the procedure. Factors that cause external invalidity include when an investigator does not use random sampling and matching the variables before the experiment. Another act that leads to external invalidity is when an investigator avoids conducting the procedure in vivo. These factors make it difficult for an observer to make generalization of other observations to other similar cases (Maxfield and Earl, 213).
Both internal and external invalidity affect the outcome of an experiment. However, internal invalidity is more serious as compared to the external invalidity. This is because the investigator does not achieve his objective in the end of the experiment. He has no confidence and cannot account for the outcome due to the internal invalidity (Maxfield and Earl, 214).
Work Cited
Maxfield, Michael G., Earl R Babbie. Basics of Research Methods for Criminal Justice and Criminology. New York: Cengage Learning, 2011.