Basics

• are the objects described in a set of data. are sometimes people. When the objects that we want to study are not people, we often call them .
• A  is any characteristic of an . A  can take different values for different .

Any set of data contains information about some group of . The information is organized in

The below figure shows part of a data set for students enrolled in an introductory statistics class. Each row gives the data on one student. The values for the different variables are in the columns. This data set has eight variables. ID is an identifier for each student. Exam1, Exam2, Homework, Final, and Project give the points earned, out of a total of 100 possible, for each of these course requirements. Final grades are based on a possible 200 points for each exam and the final, 300 points for
Homework, and 100 points for Project. Total Points is the variable that gives the composite score. It is computed by adding 2 times Exam1, Exam2, and Final, 3 times Homework plus 1 times Project. Grade is the grade earned in the course. This instructor used cut-offs of 900, 800, 700, etc. for the letter grades

1. Give the values of the variables Exam1⁽¹⁾, Exam2⁽²⁾, and Final⁽³⁾ for the student with ID equal to 105
2. A student whose data do not appear on the spreadsheet scored 88 on Exam1, 85 on Exam2, 77 for Homework, 90 on the Final, and 80 on the Project. Find Total Points⁽⁴⁾ for this student and give the grade earned⁽⁵⁾

1. The individuals are the
2. Number of variables are
3. Scores are
4. Exam1, Exam2, Homework, Final, Project, Total Points all have as the units
5. There are no for ID and grade

1. A places an individual into one of two or more groups or categories.
2. A takes numerical values for which arithmetic operations such as adding and averaging make sense.
3. The of a variable tells us what values it takes and how often it takes these values.

Suppose the data for the students in the introductory statistics class were also to be used to study relationships between student characteristics and success in the course. For this purpose, we might want to use a data set like the spreadsheet in Figure. Here, we have decided to focus on the TotalPoints and Grade as the
outcomes of interest. Other variables of interest have been included: Gender, PrevStat (whether or not the student has taken a statistics course previously),
and Year (student classification as first, second, third, or fourth year).

ID is a , total points is a , and the remaining variables are all categorical.