{"id":22814,"date":"2010-04-29T10:03:17","date_gmt":"2010-04-29T15:03:17","guid":{"rendered":"http:\/\/thesocietypages.org\/socimages\/?p=22814"},"modified":"2011-08-08T01:35:46","modified_gmt":"2011-08-08T06:35:46","slug":"methods-and-the-misleading-y-axis","status":"publish","type":"post","link":"https:\/\/thesocietypages.org\/socimages\/2010\/04\/29\/methods-and-the-misleading-y-axis\/","title":{"rendered":"Methods and the Misleading Y Axis"},"content":{"rendered":"

PART ONE:<\/strong><\/p>\n

Drinking lowers your GPA. So do smoking, spending time on the computer, and probably other forms of moral dissolution. That\u2019s the conclusion of a survey of 10,000 students in Minnesota.<\/p>\n

Inside Higher Ed reported it, as did the Minnesota press with titles like \u201cBad Habits = Bad Grades.\u201d Chris Uggen<\/a> reprints graphs of some of the \u201cmore dramatic results\u201d (that\u2019s the report\u2019s phrase, not Chris\u2019s). Here\u2019s a graph of the effects of the demon rum.<\/p>\n

\"\"<\/a><\/p>\n

Pretty impressive . . . if you don\u2019t look too closely. But note: the range of the y-axis is from 3.0 to 3.5.<\/p>\n

I\u2019ve blogged before about \u201cgee whiz\u201d graphs<\/a> , and I guess I\u2019ll keep doing so as long as people keep using them. Here are the same numbers, but the graph below scales them on the traditional GPA scale of 0 to 4.0.<\/p>\n

\"\"<\/a><\/p>\n

The difference is real \u2013 the teetotalers have a B+ average, heaviest drinkers a B. But is it dramatic?<\/p>\n

I also would like finer distinctions in the independent variable, but maybe that\u2019s because my glass of wine with dinner each night, six or seven a week, puts me in the top category with the big boozers. I suspect that the big differences are not between the one-drink-a-day students and the teetotalers but between the really heavy drinkers \u2013 the ones who have six drinks or more in a sitting, not in a week\u2013 and everyone else.<\/p>\n

—————————-<\/p>\n

PART TWO:<\/strong><\/p>\n

Some time ago, the comments<\/a> on a post here brought up the topic of the \u201cgee whiz graph.\u201d Recently, thanks to a lead from Andrew Gelman<\/a>, I\u2019ve found another good example in a recent paper.<\/p>\n

The authors, Leif Nelson and Joseph Simmons, have been looking at the influence of initials. Their ideas seem silly at first glance (batters whose names begin with K are more likely to strike out), like those other name studies<\/a> that claim people named Dennis are more likely to become dentists while those named Lawrence or Laura are more likely to become lawyers<\/p>\n

But Nelson and Simmons have the data. Here\u2019s their graph showing that students whose last names begin with C and D get lower grades than do students whose names begin with A and B.<\/p>\n

\"\"<\/a><\/p>\n

The graph shows an impressive difference, certainly one that warrants Nelson and Simmon\u2019s explanation:<\/p>\n

Despite the pervasive desire to achieve high grades, students with the initial C or D, presumably because of a fondness for these letters, were slightly less successful at achieving their conscious academic goals than were students with other initials.<\/p><\/blockquote>\n

Notice that \u201cslightly.\u201d To find out how slight, you have to take a second look at the numbers on the axis of that gee-whiz graph. The Nelson-Simmons paper doesn\u2019t give the actual means, but from the graph it looks as though he A students\u2019 mean is not quite 3.37. The D students average between 3.34 and 3.35, closer to the latter. But even if the means were, respectively, 3.37 and 3.34, that\u2019s a difference of a whopping 0.03 GPA points.<\/p>\n

When you put the numbers on a GPA axis that goes from 0 to 4.0, the differences look like this.<\/p>\n

\"\"<\/a><\/p>\n

According to Nelson and Simmons, the AB \/ CD difference was significant (F = 4.55, p < .001). But as I remind students, in the language of statistics, a significant difference is not the same as a meaningful difference.<\/p>\n","protected":false},"excerpt":{"rendered":"

PART ONE: Drinking lowers your GPA. So do smoking, spending time on the computer, and probably other forms of moral dissolution. That\u2019s the conclusion of a survey of 10,000 students in Minnesota. Inside Higher Ed reported it, as did the Minnesota press with titles like \u201cBad Habits = Bad Grades.\u201d Chris Uggen reprints graphs of […]<\/p>\n","protected":false},"author":258,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[209,23384,34,274,212],"class_list":["post-22814","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-academia","tag-social-construction-discourselanguage","tag-education","tag-methodsuse-of-data","tag-alcohol"],"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/thesocietypages.org\/socimages\/wp-json\/wp\/v2\/posts\/22814","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/thesocietypages.org\/socimages\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/thesocietypages.org\/socimages\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/thesocietypages.org\/socimages\/wp-json\/wp\/v2\/users\/258"}],"replies":[{"embeddable":true,"href":"https:\/\/thesocietypages.org\/socimages\/wp-json\/wp\/v2\/comments?post=22814"}],"version-history":[{"count":8,"href":"https:\/\/thesocietypages.org\/socimages\/wp-json\/wp\/v2\/posts\/22814\/revisions"}],"predecessor-version":[{"id":38362,"href":"https:\/\/thesocietypages.org\/socimages\/wp-json\/wp\/v2\/posts\/22814\/revisions\/38362"}],"wp:attachment":[{"href":"https:\/\/thesocietypages.org\/socimages\/wp-json\/wp\/v2\/media?parent=22814"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/thesocietypages.org\/socimages\/wp-json\/wp\/v2\/categories?post=22814"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/thesocietypages.org\/socimages\/wp-json\/wp\/v2\/tags?post=22814"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}