Download stat226_1-20-16 - Iowa State University

Stat 226 Session
Review & practice
Supplemental Instruction
Iowa State University
population
The entire group of individuals or subjects about
which we want to gain information
parameter
A numerical “summary” describing the population
of interest
Leader: Luyun
Course: Stat 226
Instructor:
Date: 1/20/16
sample
A subset of the population from which we obtain
information in order to draw conclusions about
the entire population
statistic
A numerical “ summary” describing the sample
Categorical variables:

Nominal: order not meaningful

Ordinal: order may be meaningful
Quantitative variables: take numerical values for which arithmetic operations such as adding and averaging
make sense.
True or False (explain):
1.) An observation in a data set refers to the observed value of a variable on a specific
individual.
2.) The observed outcomes of random variables (X, Y, Z) depend on some random
process and are unknown until that process occurs.
3.) “Types of stock” is an example of an ordinal, categorical variable.
4.) Inferential statistics focuses on obtaining a better understanding about the data
distribution, variability, and central tendency that a variable of interest exhibits.
5.) “We can expect 25% of all ISU students to attend the season-opening football game
during the 2013 season,” is an example of a descriptive statement.
6.) If we want to obtain information about the weight of all bluebirds in Iowa, collecting
only the weights of bluebirds in Story County would create a representative sample.
7.) If we want to obtain information about how fast people drive on Highway 30 on the
weekdays, average speed could be our variable of interest.
8.) We are interested in the average value of investment portfolios of people between the
ages of 20 and 30 years old who live in the U.S. We randomly survey 400,000 of these
people across the country and find that the average portfolio value is $26,000. $26,000 is
the population parameter.
9.) Any numerical measure computed from a subset of the population is a summary
statistic and can be observed.
1060 Hixson-Lied Student Success Center 
515-294-6624 
[email protected] 
http://www.si.iastate.edu
Main Worksheet: Describing Categorical
Data
An email survey asks 100 soon-to-be graduates (seniors) from the ISU College of Business what color of suit they
plan on wearing to the career fair this semester. (All 100 of those students plan to attend.) The resulting data can be
seen in the table below. Use this data to complete the activities and answer the questions below.
Color of Suit
Black
Brown
Blue
Tan
Purple
1.) What is the variable of interest to this survey?
2.) Is this a categorical or quantitative variable?
3.) What is the sample?
Count
74
12
10
3
1
4.) Describe the population about which we may be trying to gain information.
6.) What is the major difference between a pareto chart and a bar graph?