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Exercise

Modeling eBay auctions

Sometimes modeling a whole dataset suggests trends that disagree with models on separate parts of that dataset. This is known as Simpson's paradox. In the most extreme case, you may see a positive slope on the whole dataset, and negative slopes on every subset of that dataset (or the other way around).

Over the next few exercises, you'll look at eBay auctions of Palm Pilot M515 PDA models.

variable meaning
price Final sale price, USD
openbid The opening bid, USD
auction_type How long did the auction last?

auctions is available; dplyr and ggplot2 are loaded.

Instructions 1/2

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  • Look at the structure of the auctions dataset and familiarize yourself with its columns.
  • Fit a linear regression model of price versus openbid, using the auctions dataset. Look at the coefficients.