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STT 215 Exam 1 Questions and Correct
Answers
What is statistics? Ans: Collection or gathering of data
Displaying, analyzing, and summarizing data
Inferring information from data
Cases Ans: The objects described by a set of data. May be
customers, companies, subjects in a study, or other subjects
(observations/individuals).
Label Ans: A special variable used in some data sets to distinguish
different cases.
Example: Patient A, Patient B, Patient C, etc.
Variable Ans: A characteristic that varies among individuals in a
population or in a sample (a subset of a population).
Example: age, height, blood pressure, ethnicity, leaf length, first
language
Distribution Ans: Tells us what values the variable takes and how
often it takes these values.
Categorical variable Ans: Something that falls into one of several
categories. What can be counted is the count or proportion of
individuals in each category.
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Example: blood type (A, B, AB, O), hair color, ethnicity
Quantitative (numerical) variable Ans: Something that can be
counted or measured for each individual and then added,
subtracted, averaged, etc. across individuals in the population.
Example: height, age, blood cholesterol level
Quantitative data: discrete versus continous Ans: Discrete if the
possible values are isolated points on the number line.
Continuous if the set of possible values forms an entire interval on
the number line.
Ways to represent categorical data Ans: Frequency / Relative
Frequency distribution
Bar graph
Pie chart
Ways to represent numerical data Ans: Frequency distribution
Stemplot (stem-and-leaf plot)
Histogram
Ways to represent bivariate numerical data Ans: Scatter plot
Bar graph Ans: Each category is represented by a bar. The bar's
height shows the count (or sometimes the percentage) for that
particular category.
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Pie chart Ans: Peculiarity: the slices mist represent the parts of
one whole (1 or 100%). The size of a slice depends on what percent
of the whole this category represents.
Relative frequency Ans: (frequency) / (number of observations in
the data set)
Stemplot Ans: (Also called a stem-and-leaf plot) Each observation
is represented by a stem, consisting of all digits except the final
one, which is the leaf.
Work best for small numbers of observations that are all greater
than 0.
Display the actual values of the observations.
How to make a stemplot Ans: Separate each observation into a
stem (consisting of all but the final (rightmost) digit), and a leaf
(which is that remaining final digit). Stems may have as many
digits as needed, but each leaf contains only a single digit.
Write the stems in a vertical column with the smallest value at the
top, and draw a vertical line at the right of this column.
Write each lead in the row of its stem, in increasing order out from
the stem.
Trimming stems Ans: Trimming numbers means dropping the last
digit.
Original data 141, by dropping the last digit, it gives 14.
Splitting stems Ans: If your dataset is of median size, then even
when some numbers share same stem, we separate them into two
© 2025 All rights reserved
STT 215 Exam 1 Questions and Correct
Answers
What is statistics? Ans: Collection or gathering of data
Displaying, analyzing, and summarizing data
Inferring information from data
Cases Ans: The objects described by a set of data. May be
customers, companies, subjects in a study, or other subjects
(observations/individuals).
Label Ans: A special variable used in some data sets to distinguish
different cases.
Example: Patient A, Patient B, Patient C, etc.
Variable Ans: A characteristic that varies among individuals in a
population or in a sample (a subset of a population).
Example: age, height, blood pressure, ethnicity, leaf length, first
language
Distribution Ans: Tells us what values the variable takes and how
often it takes these values.
Categorical variable Ans: Something that falls into one of several
categories. What can be counted is the count or proportion of
individuals in each category.
© 2025 All rights reserved
, 2 | Page
Example: blood type (A, B, AB, O), hair color, ethnicity
Quantitative (numerical) variable Ans: Something that can be
counted or measured for each individual and then added,
subtracted, averaged, etc. across individuals in the population.
Example: height, age, blood cholesterol level
Quantitative data: discrete versus continous Ans: Discrete if the
possible values are isolated points on the number line.
Continuous if the set of possible values forms an entire interval on
the number line.
Ways to represent categorical data Ans: Frequency / Relative
Frequency distribution
Bar graph
Pie chart
Ways to represent numerical data Ans: Frequency distribution
Stemplot (stem-and-leaf plot)
Histogram
Ways to represent bivariate numerical data Ans: Scatter plot
Bar graph Ans: Each category is represented by a bar. The bar's
height shows the count (or sometimes the percentage) for that
particular category.
© 2025 All rights reserved
, 3 | Page
Pie chart Ans: Peculiarity: the slices mist represent the parts of
one whole (1 or 100%). The size of a slice depends on what percent
of the whole this category represents.
Relative frequency Ans: (frequency) / (number of observations in
the data set)
Stemplot Ans: (Also called a stem-and-leaf plot) Each observation
is represented by a stem, consisting of all digits except the final
one, which is the leaf.
Work best for small numbers of observations that are all greater
than 0.
Display the actual values of the observations.
How to make a stemplot Ans: Separate each observation into a
stem (consisting of all but the final (rightmost) digit), and a leaf
(which is that remaining final digit). Stems may have as many
digits as needed, but each leaf contains only a single digit.
Write the stems in a vertical column with the smallest value at the
top, and draw a vertical line at the right of this column.
Write each lead in the row of its stem, in increasing order out from
the stem.
Trimming stems Ans: Trimming numbers means dropping the last
digit.
Original data 141, by dropping the last digit, it gives 14.
Splitting stems Ans: If your dataset is of median size, then even
when some numbers share same stem, we separate them into two
© 2025 All rights reserved
