Spam is junk email. Most mail systems have a spam filter that tries to decide whether each piece of email you get is spam. When the spam filter finds something it thinks is spam, it may throw it away, or put it in a junk mail folder so that you can decide whether to throw it away without reading it. Before spam filters were a built-in feature of webmail services, people had to run their own. Say a person got about 250 emails each day. The spam filter trapped about 175 of them. Of those about five were legitimate emails and should have been delivered directly to the Inbox. The inbox, which should have contained just the legitimate messages was usually about ha spam. This particular type of spam filter was pretty good at recognizing legitimate emails but not very good at calling spams, spam. (a) Build a two-way contingency table with row categories "marked spam" and "not marked spam:, column categories "spam" and "legitimate". (b) Compute and interpret the false positive and false negative rates. (c) Explain why both the false positives and the false negatives made dealing with email harder.

A First Course in Probability (10th Edition)
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Chapter1: Combinatorial Analysis
Section: Chapter Questions
Problem 1.1P: a. How many different 7-place license plates are possible if the first 2 places are for letters and...
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Spam is junk email. Most mail systems have a spam filter that tries to decide whether each piece of email you get is spam. When the spam
filter finds something it thinks is spam, it may throw it away, or put it in a junk mail folder so that you can decide whether to throw it away
without reading it.
Before spam filters were a built-in feature of webmail services, people had to run their own.
Say a person got about 250 emails each day. The spam filter trapped about 175 of them. Of those about five were legitimate emails and
should have been delivered directly to the Inbox. The inbox, which should have contained just the legitimate messages was usually about half
spam. This particular type of spam filter was pretty good at recognizing legitimate emails but not very good at calling spams, spam.
(a) Build a two-way contingency table with row categories "marked spam" and "not marked spam:, column categories "spam" and
"legitimate".
(b) Compute and interpret the false positive and false negative rates.
(c) Explain why both the false positives and the false negatives made dealing with email harder.
(d) You can adjust the settings in the spam filter to reduce the false positive rate. Explain why that would increase the false negative rate.
(e) Is the number of spam emails received consistent with the claim in the August 6, 2008, issue of The New Yorker that there are more than a
hundred billion spam emails every day? [R315]
(f) What is the original meaning of the word "spam"? Does the company that sells (the real) spam object to the new meaning?
Transcribed Image Text:Spam is junk email. Most mail systems have a spam filter that tries to decide whether each piece of email you get is spam. When the spam filter finds something it thinks is spam, it may throw it away, or put it in a junk mail folder so that you can decide whether to throw it away without reading it. Before spam filters were a built-in feature of webmail services, people had to run their own. Say a person got about 250 emails each day. The spam filter trapped about 175 of them. Of those about five were legitimate emails and should have been delivered directly to the Inbox. The inbox, which should have contained just the legitimate messages was usually about half spam. This particular type of spam filter was pretty good at recognizing legitimate emails but not very good at calling spams, spam. (a) Build a two-way contingency table with row categories "marked spam" and "not marked spam:, column categories "spam" and "legitimate". (b) Compute and interpret the false positive and false negative rates. (c) Explain why both the false positives and the false negatives made dealing with email harder. (d) You can adjust the settings in the spam filter to reduce the false positive rate. Explain why that would increase the false negative rate. (e) Is the number of spam emails received consistent with the claim in the August 6, 2008, issue of The New Yorker that there are more than a hundred billion spam emails every day? [R315] (f) What is the original meaning of the word "spam"? Does the company that sells (the real) spam object to the new meaning?
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