Question

One of the following experiments has an internal validity problem and the other does not. First, identify which experiment DOES NOT have an internal validity problem. Next, for the remaining experiment, identify at least one problem that threatens the internal validity.

a. A cognitive psychologist believes that people learn better when they spread out their studying over several days, so she creates a study with three groups of participants. Each group studies the same list of 120 Chinese vocabulary words (none of the participants had studied Chinese before). One group studies the words for 20 minutes on the first day. The second group studies the words for 20 minutes on the first and second days. The last group studies the words for 20 minutes on the first, second, and third days. On the fourth day, all of the participants are tested on how well they have learned the Chinese vocabulary words. The people in the last group scored the best, so the researcher concludes that distributed studying does improve people’s ability to learn.

b.A human factors psychologist is comparing visibility features for automobiles. (Human factors psychologists study how humans interact with the material world.) He plans to test whether drivers will avoid obstacles behind their cars more effectively when the car is equipped with an enhanced rearview mirror, a rear video camera system, or an object detector that sets off a buzzer alarm. He places a sample of 25 drivers into each of three cars. The cars are identical except for their object detectors. The drivers spend 1 hour familiarizing themselveswith their vehicles and their object detectors by running through a set of drills on a closed driver’s course. During a test phase, the researcher places a set of objects behind each driver. The test objects range in height, color, and movement. Each driver attempts to back up his or her car while avoiding each of the test objects. Each object is presented three times each. The psychologist finds that, on average, drivers respond more accurately to the rear camera video system compared to the rearview mirror or the buzzer alarm.

Answer 1

The second experiment DOES NOT have an internal validity problem where as the first one DOES.

First experiment : The psychologist believes that people learn better when they spread out their studying for several days. But in the experiment, he test people who studied for 20 minutes, 40 minutes, 60 minutes. What he tested is by giving different amount of time to study. But for his experiment, this is not going to give him valid results. He should in the following way.

Team 1 : 1st day - 20 minutes

Team 2 : 1st day - 10 minutes and 2nd day - 10 minutes

Team 3 : 1st day - 7 minutes, 2nd day - 7 minutes, 3rd day - 8 minutes.

In this way he will get the desired results.