e-Statistics
e-Statistics
For Students
For Contributors
Data in Statistical Studies
Textbook Data Sets
Worksheet Data Sets
Data and Story Library
Exploratory Graphics
Stem and Leaf Plot
Histogram
Boxplot
Scatter Plot
QQ plot
Bar Graph
Descriptive Statistics
Summary Statistics
Frequency Table
Grouped Data
Transformed Data
Normal Distribution
Normal Density Function
Z-score
Critical Value
Central Limit Theorem
Discrete Distributions
Binomial Distribution
Frequency Function
Normal Approximation
Inference on Mean
t-Distribution
Confidence Interval
Hypothesis Test
Power of Test
One-sided CI
Comparison of Two Groups
Test for Independent Groups
Nonparametric Test
Test for Paired Data
Simple Linear Regression
Regression Line
R Square
Residual Plot
Inference on Parameters
Predicting Responses
One-Way ANOVA Model
F-Distribution
Analysis of Variance
Strip Chart
Multiple Comparisons
Multiple Linear Regression
Model Estimate and Residuals
Model Selection and F-test
Two-Way Additive Model
Test of Effect
Analysis of Variance
Inference on Variances
Testing a Standard Deviation
Test for Two Groups
Test for Homogeneity
Inference on Proportions
Testing a Proportion
Comparison of Two Proportions
Chi-square Test
Chi-square Distribution
Goodness of Fit
Test for Homogeneity
Logistic Regression
Inference on parameters
Adjusted log OR

Boxplot

A boxplot is a schematic presentation of summary statistics: a measure of center (sample median), a measure of variation (IQR between lower and upper quartiles), and the largest and smallest data. It also indicates the symmetry or skewness of the distribution and the presence of possible outliers. The plot will be displayed.

A box in the middle of boxplot stretches from the lower quartile Q1 (the 25-percentile) to the upper quartile Q3 (the 75-percentile). The median Q2 is shown as a line across the box. Therefore, 1/4 of the observations lies between this line and the right of the box and 1/4 of the observation between this line and the left of the box. Straight lines (either horizontal or vertical) are called whiskers, stretching out from the ends of the box to the largest and smallest value, Q0 and Q4. In the computer-generated boxplot potential outliers will be indicated separately from whiskers.

The data of one variable are often grouped by another categorical variable. Such a categorical variable is often referred as “factor,” and its values are called “levels.” The presentation of side-by-side boxplots is quite useful for comparing the data from different groups (i.e., different levels).

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