Statistics

1. If you are told only that you scored in the 80th percentile, do you know from that description exactly how it was calculated? Explain.

2. For the numbers 1, 2, 4, 16, compute the following:
ΣX
ΣX2
(ΣX)2

3. (TR) What is the independent variable in this study? (Case Study Below)

CASE STUDY FOR QUESTION 3
OVERVIEW
How powerful are rumors? Frequently, students ask friends and/or look at instructor evaluations to decide if a class is worth taking. Kelley (1950) found that instructor reputation has a profound impact on actual teaching ratings, and Towler and Dipboye (1998) replicated and extended this study.

Subjects were randomly assigned to one of two conditions. Before viewing the lecture, students were given a summary of the instructors’ prior teaching evaluations. There were two conditions: Charismatic instructor and Punitive instructor.

Then all subjects watched the same twenty-minute lecture given by the exactsame lecturer. Following the lecture, subjects answered three questions about the leadership qualities of the lecturer. A summary rating score was computed and used as the variable “rating” here.

QUESTIONS TO ANSWER
Does an instructor’s prior reputation affect student ratings?

DESIGN ISSUES
The data presented here are part of a larger study. See the references below to learn more.

DESCRIPTIONS OF VARIABLES
VARIABLE DESCRIPTION
Condition this represents the content of the description that the students were given about the professor (1 = charismatic, 2 = punitive)
Rating how favorably the subjects rated the professor after hearing the lecture (higher ratings are more favorable)

3. (AT) What is the independent variable of this experiement? How many levels does it have? (*Case Study Below)

CASE STUDY FOR QUESTION 4
Overview
This study investigated the cognitive effects of stimulant medication in children with mental retardation and Attention-Deficit/Hyperactivity Disorder. This case study shows the data for the Delay of Gratification (DOG) task. Children were given various dosages of a drug, methylphenidate (MPH) and then completed this task as part of a larger battery of tests. The order of doses was counterbalanced so that each dose appeared equally often in each position. For example, six children received the lowest dose first, six received it second, etc. The children were on each dose one week before testing.
This task, adapted from the preschool delay task of the Gordon Diagnostic System (Gordon, 1983), measures the ability to suppress or delay impulsive behavioral responses. Children were told that a star would appear on the computer screen if they waited “long enough” to press a response key. If a child responded sooner in less than four seconds after their previous response, they did not earn a star, and the 4-second counter restarted. The DOG differentiates children with and without ADHD of normal intelligence (e.g., Mayes et al., 2001), and is sensitive to MPH treatment in these children (Hall &Kataria, 1992).
Questions to Answer
Does higher dosage lead to higher cognitive performance (measured by the number of correct responses to the DOG task)?

Design Issues
This is a repeated-measures design because each participant performed the task after each dosage.

Descriptions of Variables
Variable Description
d0 Number of correct responses after taking a placebo
d15 Number of correct responses after taking .15 mg/kg of the drug
d30 Number of correct responses after taking .30 mg/kg of the drug
d60 Number of correct responses after taking .60 mg/kg of the drug
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Use the following information to answer the next three exercises: A Lake Tahoe Community College instructor is interested in the mean number of days Lake Tahoe Community College math students are absent from class during a quarter. (and why?)
1. What is the population she is interested in?
a. all Lake Tahoe Community College students
b. all Lake Tahoe Community College English students
c. all Lake Tahoe Community College students in her classes
d. all Lake Tahoe Community College math students

2. The instructor’s sample produces a mean number of days absent of 3.5 days. This value is an example of a: (and why?)
a. parameter.
b. data.
c. statistic.
d. variable.

3. A study was done to determine the age, number of times per week, and the duration (amount of time) of residents using a local park in San Jose. The first house in the neighborhood around the park was selected randomly and then every eighth house in the neighborhood around the park was interviewed. The sampling method was: a. simple random b. systematic c. stratified d. cluster

4. Fifty part-time students were asked how many courses they were taking this term. The (incomplete) results are shown below:
# of Courses Frequency Relative Frequency Cumulative Relative Frequency
1 30 0.6 ??? 2 15 ??? ??? 3 ??? ??? ???
Table 1.33 Part-time Student Course Loads
a. Fill in the blanks (???) in Table 1.33.

b. What percent of students take exactly two courses?

c. What percent of students take one or two courses?