Research Methods

External Validity

Strayer, D. L., Drews, F. A., & Johnston, W. A. (2003). Cell phone-induced failures of visual attention during simulated driving. Journal of Experimental Psychology: Applied, 9, 23-32.

Strayer, Drews, and Johnston (2003) conducted four experiments to determine why cell-phone conversations distract people more than other activities. Using 110 undergraduates, the researchers used a driving simulator that law enforcement agencies rely on; it is nearly identical to the driver’s portion of a Ford Crown Victoria. The testing situation includes screens that show a realistic driving environment.
Sometimes students who drove the simulator also spoke on a cell phone, conversing with another student who was instructed to keep a balance between making the driver talk and listen. Only hands-free cell phones were used in the study so the researchers could avoid any distracting effects from handling phones, and focus on distracting effects of conversation.
Strayer et al. (2003) found that drivers are more accident-prone and slower to react because they cannot process visual information as well when using a cell phone as when they are merely talking to somebody, even with hands-free models. The researchers call this deficit to "inattention blindness".

QUESTION: Are these results likely to be similar if applied to drivers other than college students? What variables might be important in generalizing from this sample?


Bryant, A. N. (2003). Changes in attitudes toward women's roles: Predicting gender-role traditionalism among college students. Sex Roles, 48, 131-142.

Bryant used national college student data derived from surveys in 1996 and 2000 to assess longitudinal changes in gender-role traditionalism across 4 years of college. Using a psychological model of behavior analyze the data, Bryant looked at students' precollege characteristics and predispositions, and various college environments and experiences, and she used them to predict the changes in male and female students across their college years.
Findings indicated that students' levels of traditionalism declined during college. Men and women tended to change similarly regarding traditionalism. Further, women held more egalitarian views than did men at college entry and 4 years later. Statistical analysis revealed the importance of (a) one’s peers, (b) academic engagement, (c) women's studies courses, and (d) diversity experiences for students' gender-role attitudes 4 years after college entry.

QUESTION: Do you think the changes in student attitudes and dispositions reported here are likely to be similar to the changes that occur in non-college people of the same age? Or will the results pertain only to college students? Would these results replicate for college students who are older and who are returning to school after working for several years? Explain your thoughts.


Tonkiss, J., Galler, J. R., Shukitt-Hale, B., & Rocco, F. J. (1991). Prenatal protein malnutrition impairs visual discrimination learning in adult rats. Psychobiology, 19, 247-250.

Female rats received diets containing low or adequate amounts of protein for 5 weeks prior to mating and throughout pregnancy. As a result, the rats resulting from this mating were either malnourished or adequately nourished during the prenatal period, depending on which condition they were in. All pups received adequate nutrition from the day of birth onwards
The offspring were tested on the Lashley jump stand in 3 visual discrimination problems, beginning at 91 days of age. Rats who were malnourished because their mothers received insufficient protein made more errors overall and were slower to learn visual discrimination tasks involving a vertical- vs horizontal-stripe discrimination task. Thus, it appears that if a rat is malnourished during pregnancy, her offspring may face long-term visual deficits.

QUESTION: Are these results likely to hold true for other animals? Would the results replicate if this type of unethical experiment were done on people? That is, can you generalize from rats to people in this instance? Justify your response.