Will anybody buy? Logistic regression - Improving the User Experience through Practical Data Analytics - page 272

SIDEBAR: WHY CAN'T I USE REGULAR REGRESSION?
Regular linear regression models (whether simple or multiple) are not appropriate for binary
responses for a couple of reasons. First, the assumptions that underlie them are violated to too large
an extent. For example, one of our assumptions in Chapters 9 and 10 is that if we had a bunch of
data values with the same set of X's, the Y's would form a bell-shaped (normal) curve. Here, the Y
“curve” would be not even close to that, being just a set of 1's and a set of 0's—two vertical lines
on a graph. In addition, some of the theory of binary logistic regression differs from regular linear
regression; for example, the best itting line is not chosen by the criterion of least squares.
If we did ind the least-squares regression line when the Y data that yielded the line is 1 and 0,
there's a possibility that the resulting Yc can actually be greater than 1 or less than 0. Both of these
are theoretically meaningless, since we interpret Yc as the probability of obtaining a 1. Thus is
another reason we use logistic regression, which does not allow a Yc outside of the (0,1) range.
11.2 CASE STUDY: WILL ANYBODY BUY
AT THE CHARLESTON GLOBE ?
You've just been hired as a UX researcher at the CharlestonGlobe.com, a subscrip-
tion-based Web site afiliated with the Charleston Globe , a newspaper based in
Charleston, Massachusetts.
The Charleston Globe has a long and noble history, established in 1862, garnering
no fewer than 38 Pulitzer Prizes since 1966. When the Internet changed everything in the
early 1990s, the Globe hopped on the bandwagon early, creating CharlestonGlobe.com,
a free, albeit stripped-down, version of the paper in 1995. Then fast forward to 2011, and
the new owners decided to gamble on subscription-based Web site, CharlestonGlobe.
com, where the entire contents of print version are posted behind a paywall.
The new site is slick; its response design automatically adapts its layout to your
device's screen size, whether you're using a laptop, tablet, smartphone, or just about
any Web-reading device you can imagine. The site also contains every single word of
the paper version along with some “premium content.” Current paper subscribers are
given free access to CharlestonGlobe.com, but all others must break out their credit
cards and plop down $3.99 a week.
And that's the rub, because very few Charlestonians—or anybody else—are
breaking out their credit cards. The numbers are abysmal, and it's got the new own-
ers scratching their heads.
Their game plan seemed to make sense at the time. With the inevitable decline
of paper subscriptions, and with an ever-increasing percentage of Americans getting
their news online at free sites like CNN.com and Googlenews.com , the new owners
thought they had a solution custom-built for the current trend: an online version of
the paper that was convenient, comprehensive, and accessible everywhere—without
the hassle of recycling.
Now they're wondering where they went wrong and have turned to the Digital
Product team to igure it out. After all, your group produces and runs the site, so you
should be able to diagnose and rectify the problem. It doesn't really matter to the new
owners that American news consumption has been altered more in the past 10 years
that since the advent of television, and that just about every mass media company is