Experimental Research Two, Term Paper Example

There are four different threats to internal validity: intact groups, extraneous variables, subject loss, and expectancies.  Any one of these threats could make an experiment invalid.  The threat of intact groups refers to groups that are formed prior to the start of an experiment.  An example of an intact group would be a group of students in a particular class at a university. Extraneous variables refers to decisions that have been made about the experiment that ultimately lead to a confounding.  This type of threat most often occurs when experimenters create different methods or group sizes within an experiment.  Subject loss, is another common type of threat and refers to participants in an experiments dropping out or having to remove themselves from the experiment for one reason or another. Lastly, the fourth type of threat to internal validity is expectancies.  Expectancies occur when participant’s performance can be persuaded according to demand characteristics (Zechmeister 172).

Based on the information given about the experiment of the memory drug we can conclude that the drug may be somewhat successful. We need to take into consideration whether or not any of the four threats of internal validity came into play. Of these four threats the one that sticks out the most as being problematic for the experiment described is the threat of expectancy.  As far as intact g groups are concerned, there is not much threat since a random group of students from KU were picked.  In the experiment there is also small chance that an extraneous variable occurred since there is only one experimenter doing this experiment. Also the experiment did not mention that any of the students had dropped out of the experiment this, therefore, eliminates the threat of subject loss.

The one threat this experimenter does need to be concerned about is the threat of expectancy.  S/he clearly had a bias as to believing the drug itself worked.  Even though he may have been determined to not let his personal beliefs get in the way of the experiment since it was conducted solely by this experimenter we cannot rule out that his own personal biases did not come into play.

In this experiment there is also the matter of external validity.  External validity is “the degree to which the conclusions in your study would hold for other persons in other places and at other times”(Trochim p.1). Thinking of external validity allows us to examine whether or not this experiment can be applied to general public. The experiment concerning the memory drug may be questionable as far as external validity is concerned because of the population of the participants.  While it is admirable that the experimenter chose a random sample of students, it is also important to note that the general public does not fall into the category of college students.  There are distinctive differences among college students and the general population.  The differences include age and health to name only two.  College students typically are younger than people most likely to seek this type of drug out, and it is also true that college students tend to be healthier than the general public, partly due to their youth.  If we truly want a random sample the experimenter needs to pick people of varying age groups to make the results more conclusive.

Works Cited

Trochim, W.  Research Methods Knowledge Base.  Web Center for Social Research Methods. 2006; http://www.socialresearchmethods.net/kb/external.php.

Zechmeister, J., Zechmeister, E., Shaughnessy, J. Essentials of Research Methods in Psychology. 2001 McGraw-Hill.