Question

1. a recent study with 60 middle school students was conducted to try to determine if reading comprehension was affected by the mode in which students were reading (digital or print). half of the students were randomly assigned to read a passage on printed paper and the other half were assigned to read the passage on a digital device. the students were then asked to complete a reading comprehension test and their scores were recorded.

a. why is this study considered an experiment instead of an observational study?
b. identify experimental units and treatments.
c. describe a process that could be used to do the random assignment.
d. the researchers are planning to conduct another similar experiment, but they are concerned that the grade level (6th, 7th, or 8th) of the students is strongly associated with the comprehension test results. propose a possible solution for this concern.

Explanation:

a. In an experiment, the researcher manipulates an independent variable (here, the reading mode - digital or print). In an observational study, the researcher only observes without manipulating. Here, students were assigned (manipulated) to different reading modes.
b. Experimental units are the entities on which the experiment is performed. Treatments are the different conditions.
c. Random assignment methods involve using a random - based technique to divide the group.
d. Blocking is a technique used when a variable (like grade level) is suspected to affect the response variable (reading comprehension scores).

Answer:

a. This is an experiment because the researchers assigned (manipulated) the students to different reading modes (digital or print). In an observational study, there is no such manipulation; researchers just observe.
b.

• Experimental units: The 60 middle - school students.
• Treatments: Reading a passage on printed paper and reading a passage on a digital device.

c. One process for random assignment could be: Number each of the 60 students from 1 to 60. Use a random number generator to generate 30 distinct numbers between 1 and 60. The students with the generated numbers are assigned to the print - reading group, and the remaining 30 students are assigned to the digital - reading group.
d. The researchers can use blocking. For example, they can create three blocks: 6th - grade students, 7th - grade students, and 8th - grade students. Then, within each block, randomly assign half of the students in the block to the print - reading group and the other half to the digital - reading group. This way, the effect of grade level (which is associated with reading comprehension) is controlled for.