{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Threats+to+validity-handout

Threats+to+validity-handout - Threats to Internal Validity...

Info icon This preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Threats to Internal Validity * Internal Validity deals with whether or not the experimental treatments made a difference in this one, specific instance. Did the manipulation of the independent variable really cause what we see at the end of the study? Campbell & Stanley (1963) identified 7 key issues (and their interactions) that threaten the internal validity of a study: Selection The results of your study might be due to a pre-existing difference between groups in the study. For example, you want to study the effectiveness of new method for teaching math. You visit a local school and select two classes to try out your experiment with. In the first class you teach math using a traditional approach, but in the second class you teach using your new method. In the end you give both classes a test to measure how much they know, and those in the new method condition score better. BUT, what you did not know is that the class that got the new method was an advanced placement math course and the other class was a remedial math course. So, in the end you do not know whether it was a difference in teaching methods or some pre-existing difference in math ability that created the difference at the end. Statistical Regression to the Mean This in an effect that happens when dealing with people at the extremes of a population. Because our measures are not perfect, repeated testing will result in a move towards the average of the population. For example, you want to test a new method of teaching math to remedial students. In order to select your subjects you give them a pre-test and select the lowest 10% of scores. You then try to teach them using your new method, followed by a post-test. It turns out that the average of your sample goes up. BUT: Because of imperfections in measurement, we would expect this to happen regardless of what happened to them. So, we don’t know if the increase was due to the teaching method or if it was just a statistical artifact created by imperfect measurement. Maturation Biological and psychological process of subjects will change with the passage of time. Subjects will get hungry, fatigued, etc. during the course of an experiment, and these changes can create a confound that masks the true effect of an experimental manipulation. For example, at the start of your experimental you have a group of subjects tracing a pattern on a sheet of paper. The experimental condition receives loud bursts of noise in the background, while the control group is kept in a quiet room. After several
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern