Groups and a between-groups design

What is the difference between a within-groups and a between-groups design? What are the relative advantages and disadvantages of each type of design?
A behavioral researcher wanted to determine whether eating sugary cereal for breakfast increased the aggression of first graders during their morning play period. After feeding a group of 20 students sugary cereal for breakfast she observed that, on average, the students committed 5.1 aggressive behaviors during their morning play period. In this example, the descriptive statistic is:
a. the 20 students the researcher observed.
b. all first graders.
c. all first graders who ate sugary cereal for breakfast.
d. the 5.1 aggressive behaviors.
A behavioral researcher wanted to determine whether eating sugary cereal for breakfast increased the aggression of first graders during their morning play period. After feeding a group of 20 students sugary cereal for breakfast she observed that, on average, the students committed 5.1 aggressive behaviors during their morning play period. In this example, the population is:
a. the 5.1 aggressive behaviors.
b. the 20 students the researcher observed.
c. all first graders who eat sugary cereal for breakfast.
d. all first graders.
Dietz and Henrich (2014) were interested in the impact of texting on student learning. A group of 99 college students were randomly assigned to text (N = 50) or not text (N = 49) during a pre-recorded psychology lecture. At the end of the 20 minute lecture, students answered a 17 question quiz about the material that had just been presented. On average, the researchers found that students who texted during the lecture answered fewer quiz questions correctly as compared to students who hadn’t texted during the lecture. Which of these requires an inferential statistic?
a. the conclusion that texting interferes with student learning
b. the average performance on the post-lecture quiz
c. recruiting the sample of 99 college students
d. the random assignment of students into texting and non-texting groups
A behavioral researcher interested in the concept of preparedness sets up a booth at a local mall. His idea is to compare men and women in terms of what they carry on their person, and to evaluate what types of events or issues they are prepared to handle based on what they are carrying with them. He has chosen a mall setting because people are readily available. In this sense, people at the mall are a:
a. random sample.
b. selected sample.
c. convenience sample.
d. random assignment.
A local United Way and a group of community agencies in a large urban area have decided that making sure young children are ready to enter the school system is a high priority for the community. They hire a group of educational researchers to assess the school readiness of individual children entering the 120 kindergarten classrooms in the area. (a) What is the population of interest? (b) Why would the researchers choose to assess a sample rather than the entire population? (c) Is random selection possible in this case? Explain why or why not.
Dr. Lofgren was interested in the effects of test anxiety on concentration abilities. Using an anxiety questionnaire, he measured student anxiety levels when the students arrived at his laboratory and then again immediately before taking an examination. Dr. Lofgren hypothesized that participants in his study would have higher anxiety scores immediately prior to the completion of the exam compared to when they first came in. As hypothesized, Dr. Lofgren found that participants’ anxiety scores were significantly higher immediately prior to the examination compared to baseline scores. As a result of this information, what type of t test was Dr. Lofgren MOST likely to use to test his hypothesis? Is Dr. Lofgren’s hypothesis test one-tailed or two-tailed? Explain your answers.
The expected value for an F ratio is equal to 1.00 when there is no treatment effect. Why?
Research coming out of the Developmental Labs, Inc., of Huntington, New York, established that reading skill was positively correlated with smooth movements of the eyes during reading (i.e., fewer pauses and fewer retracks). A friend suggests that the local school district invest money in equipment that teachers could use to help students better move their eyes so that reading skill can be improved. How would you respond to this friend’s recommendation?
A psychopathology researcher was interested in determining whether her interventions for depression were effective in minimizing depression symptoms among her participants. To assess the effectiveness of her treatment program, she administered a depression inventory prior to treatment and after treatment. She hypothesized that depression scores would be lower at Time 2 compared to Time 1. She then compared the mean differences between the two groups and found that her treatment was effective. Which statistical test was the researcher MOST likely to have used to test her hypothesis?
a. independent-samples t test
b. z test
c. single-sample t test
d. paired-samples t test
Dr. Simon wanted to know if IQ scores differed between male and female participants in his study. He gave 26 participants an IQ test and then examined IQ scores for gender differences. He hypothesized that there would be a statistically significant gender difference in IQ scores. Contrary to Dr. Simon’s hypothesis, there were no differences in IQ scores between men and women in his study. What is the independent variable in this study?
a. participants
b. gender
c. sample size of 26
d. IQ scores
The correlation coefficient between the variables, height and IQ score, is zero. What does this statement mean? a. As the value of one variable changes the other increases.
b. The scores of the two variables are evenly matched.
c. As the value of one variable changes the other decreases.
d. As the value of one variable changes the other is not necessarily affected.
The observation of a positive correlation between head size and foot size indicates that:
a. people with larger feet tend to have smaller heads.
b. people with larger feet also tend to have larger heads.
c. having a large head causes a person to have large feet.
d. having large feet causes a person to have a large head.
When would you use an ANOVA instead of a T test and why? Be specific.
Explain how we use expected relative-frequency probability to infer what a population looks like. (Hint: It’s the lecture with the green and red marbles).