{"id":722,"date":"2017-02-11T08:41:12","date_gmt":"2017-02-11T08:41:12","guid":{"rendered":"https:\/\/blogs.scu.edu\/dataviz\/?p=722"},"modified":"2017-02-11T19:47:34","modified_gmt":"2017-02-11T19:47:34","slug":"understanding-a-box-plot","status":"publish","type":"post","link":"https:\/\/blogs.scu.edu\/dataviz\/2017\/02\/11\/understanding-a-box-plot\/","title":{"rendered":"Understanding a Box plot"},"content":{"rendered":"<p>I personally have never used a box plot because I didn\u2019t know how to use it and when to use it. But when Professor explained in last lecture about average violations per day using box plot, I found it more appealing. Box plots are great way to quickly examine one or more datasets graphically. Of course, you need to know the meaning of all fields on a box plot to understand it. Here is an easy and simple example of how to interpret a box plot.<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/visualoop.com\/media\/2015\/04\/box_plot_anatomy.png\" \/><\/p>\n<ul>\n<li>Box plot (aka Box and Whisker Plot) plots all data points and splits it into <a href=\"https:\/\/www.mathsisfun.com\/data\/quartiles.html\">quartiles<\/a> (Q1, Q2, Q3) and it is represented as a box which goes from first quartile to third quartile.<\/li>\n<li>The vertical line drawn at the Q2 is median of data set.<\/li>\n<li>Two horizontal lines extend from front and back of the box are called whiskers. Whiskers often (but not always) stretch over a wider range of scores than the middle quartile groups.<\/li>\n<li>The extreme points preceding first quartile and \u00a0following third quartile are known as <a href=\"http:\/\/stattrek.com\/statistics\/dictionary.aspx?definition=Outlier\">outliers<\/a>.<\/li>\n<\/ul>\n<p>We can display three common measures of the distribution in data set.<\/p>\n<ol>\n<li><strong>Range: <\/strong>It is the distance between two extreme points on a plot. If we consider outliers, then it is between (5) to (95)-&gt; 90. If we exclude outliers, then it is (95-15) 80.<\/li>\n<li><strong>Interquartile range:<\/strong> The middle half of a data set falls within the interquartile range. In a boxplot, the interquartile range is represented by the width of the box (Q3 minus Q1). In the chart above, the interquartile range is (80-38) 42.<\/li>\n<li><strong>Skewness: <\/strong>We can identify different <a href=\"http:\/\/stattrek.com\/statistics\/dictionary.aspx?definition=Skewness\">skewness<\/a> patterns based on shape of dataset. If the data points are concentrated at the lower end, the distribution is skewed right and vice-versa. If it is evenly split at the median then it is Symmetric.<\/li>\n<\/ol>\n<p>In Speed Violations example, we can easily identify danger zones which are nothing but those outliers in box plot. Also, our grades distribution on Camino is also a box plot which gives you where your grades stand in overall class grades, what is the average score and how many are above\/below average.<\/p>\n<p>I am trying to create a box plot in Tableau, if anybody has already done please share!<\/p>\n<p>Source:\u00a0<a href=\"http:\/\/www.datavizcatalogue.com\/methods\/images\/anatomy\/box_plot.png\">http:\/\/www.datavizcatalogue.com\/methods\/images\/anatomy\/box_plot.png<\/a><\/p>\n<p>http:\/\/stattrek.com\/statistics\/charts\/boxplot.aspx<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>I personally have never used a box plot because I didn\u2019t know how to use it and when to use it. But when Professor explained in last lecture about average violations per day using box plot, I found it more appealing. Box plots are great way to quickly examine one or more datasets graphically. Of &hellip; <a href=\"https:\/\/blogs.scu.edu\/dataviz\/2017\/02\/11\/understanding-a-box-plot\/\" class=\"more-link\">Continue reading <span class=\"screen-reader-text\">Understanding a Box plot<\/span><\/a><\/p>\n","protected":false},"author":1854,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"qubely_global_settings":"","qubely_interactions":"","kk_blocks_editor_width":"","_kiokenblocks_attr":"","_kiokenblocks_dimensions":"","footnotes":""},"categories":[1],"tags":[],"class_list":["post-722","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"gutentor_comment":0,"qubely_featured_image_url":null,"qubely_author":{"display_name":"vinamrata","author_link":"https:\/\/blogs.scu.edu\/dataviz\/author\/vinamrata\/"},"qubely_comment":0,"qubely_category":"<a href=\"https:\/\/blogs.scu.edu\/dataviz\/category\/uncategorized\/\" rel=\"category tag\">Uncategorized<\/a>","qubely_excerpt":"I personally have never used a box plot because I didn\u2019t know how to use it and when to use it. But when Professor explained in last lecture about average violations per day using box plot, I found it more appealing. Box plots are great way to quickly examine one or more datasets graphically. Of&hellip;","post_mailing_queue_ids":[],"_links":{"self":[{"href":"https:\/\/blogs.scu.edu\/dataviz\/wp-json\/wp\/v2\/posts\/722","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.scu.edu\/dataviz\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.scu.edu\/dataviz\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.scu.edu\/dataviz\/wp-json\/wp\/v2\/users\/1854"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.scu.edu\/dataviz\/wp-json\/wp\/v2\/comments?post=722"}],"version-history":[{"count":6,"href":"https:\/\/blogs.scu.edu\/dataviz\/wp-json\/wp\/v2\/posts\/722\/revisions"}],"predecessor-version":[{"id":735,"href":"https:\/\/blogs.scu.edu\/dataviz\/wp-json\/wp\/v2\/posts\/722\/revisions\/735"}],"wp:attachment":[{"href":"https:\/\/blogs.scu.edu\/dataviz\/wp-json\/wp\/v2\/media?parent=722"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.scu.edu\/dataviz\/wp-json\/wp\/v2\/categories?post=722"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.scu.edu\/dataviz\/wp-json\/wp\/v2\/tags?post=722"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}