DE Stats Unit 1

Individuals

Objects described by a set of data; may be people, animals, or things.

Variable

Any characteristic of an individual; can take different values for different individuals.

Categorical Variable

A variable that places an individual into one of several groups or categories.

Quantitative Variable

A variable that takes numerical values for which arithmetic operations make sense.

Distribution

Tells what values a variable takes and how often it takes these values.

Frequency Table

A table that shows the number of times each item or number appears in a dataset.

Relative Frequency

The proportion or percent of the total observations that fall into each category.

Pie Chart

A circular chart divided into sectors, each representing a category’s proportion of the whole.

Bar Graph

A chart with bars whose lengths represent the frequencies or relative frequencies of categories.

Two­Way Table

A table that organizes data about two categorical variables.

Marginal Distributions

The distribution of values of one variable among all individuals described by the table.

Conditional Distribution

The distribution of a variable restricted to individuals who satisfy a condition on another variable.

Segmented Bar Graph

A bar graph where each bar is divided into segments that represent different categories within the bar.

Association

A relationship between two variables if knowing the value of one helps predict the value of the other.

Dotplot

A simple graph that shows each data value as a dot above its location on a number line.

Shape

The overall appearance of a distribution (e.g., symmetric, skewed, uniform).

Center

A value that attempts to summarize the entire distribution with a single number (mean or median).

Spread

A measure of how much the values in a dataset vary (range, IQR, standard deviation).

Variability

The extent to which data points differ from each other.

Outlier

An observation that lies outside the overall pattern of the distribution.

Symmetric (graphs)

A graph where the left and right sides are roughly mirror images of each other.

Skewed to the Right

A distribution with a long tail on the right side.

Skewed to the Left

A distribution with a long tail on the left side.

Bimodal

A distribution with two clear peaks.

Multimodal

A distribution with more than two peaks.

Stemplot

A graphical method of displaying quantitative data using stems and leaves.

Splitting Stems

A technique in stemplots to spread out the data by splitting each stem into two or more parts.

Back­to­Back Stemplot

A stemplot used to compare two related distributions by placing them on either side of the stems.

Histogram

A graph of vertical bars representing the frequency distribution of a set of data.

Mean

The arithmetic average of a set of numbers.

Median

The middle value in an ordered dataset; half the data are above, half below.

Resistant Measure

A statistic that is not affected much by extreme observations (e.g., median).

Range

The difference between the maximum and minimum values in a dataset.

Boxplot

A graphical display of the five-number summary of a distribution.

First Quartile

The median of the lower half of the data; 25th percentile.

Third Quartile

The median of the upper half of the data; 75th percentile.

Interquartile Range

The distance between the first and third quartiles (Q3 – Q1).

Five Number Summary

The minimum, Q1, median, Q3, and maximum of a dataset.

Standard Deviation

A measure of the average distance of each data point from the mean.

Variance

The square of the standard deviation; measures spread in a dataset.