Editing 2892: Banana Prices

{{comic
| number    = 2892
| date      = February 9, 2024
| title     = Banana Prices
| image     = banana_prices_2x.png
| imagesize = 564x378px
| noexpand  = true
| titletext = It's a linear extrapolation, Michael. How big could the error be? 10%?
}}

==Explanation==
{{incomplete|Created by a MANDALORIAN BANANA ARMORER - Please change this comment when editing this page.}}

[https://www.youtube.com/watch?v=Nl_Qyk9DSUw ‘It’s one banana, Michael. What could it cost, $10?'] is a line from an {{w|Arrested Development}} episode (Season 1, Episode 6, "Charity Drive", 2003) that became a well-known meme used to mock out-of-touch elites. The character who spoke this line (Lucille Bluth, a rich socialite) made a satirically high estimate for the price of a banana because she had never bought her own groceries.  According to the graph, the banana price at the time of that episode was actually just under 25 cents, and the price at the time of this comic’s publication (2024) is around 30 cents.

This comic channels Lucille Bluth’s confident ignorance to provide a graph and its conclusions that are similarly satirical in their ignorant simplicity and statistical illiteracy. This mechanism serves to illustrate a number of ways to violate statistical best practices and to "lie with data." The additional use of an "unreliable narrator" device (embodied by the caption writer) gives this comic several layers of meaning.

The comic is a wry observation that the irony of this sitcom line will "probably" be obsolete in a century or so. This comic shows a graph of three predicted prices for bananas over the next 250 years, extrapolating from the current price. The three extrapolations use (1) the general inflation rate (a value dominated by the cost of housing), (2) the inflation rate for fresh fruit, and (3) 45 years of historic banana prices. The comic presents these extrapolations to claim that in a century or so the irony of the sitcom quote is likely to be anachronistically meaningless. 

The caption’s claim that banana prices could exceed $10 in a century are based on the fastest rising extrapolation, the one for “general inflation.” This extrapolation predicts a banana’s price to rise from 30 cents to $10 in approximately 115 years. This 115-year increase corresponds to an average long-term inflation rate of about 3.2%, close to the historic US average.

The reference to "BLS/St. Louis Fred" refers to The {{w|Bureau of Labor Statistics}} and {{w|St. Louis Fed Financial Stress Index|St Louis ''Fed''}}, widely respected sources of economic data.

The title text continues the ignorant tone of Lucille Bluth to satirically guess an error less than 10%. In act, the three predictions themselves (from 115 years to 220 years) differ by over 80%. So the Bluthian speaker is satirically presuming far more accuracy from a multi-century prediction than is warranted. Just as Lucille was very wrong about a $10 banana (a price threshold), so, too, is the Bluthian speaker of the title text very wrong about the 10% error (a proportional change). This is a meta-joke about the false precision of extrapolations. Randall is using the voice of Lucille Bluth to acknowledge the high uncertainty of these extrapolations.

Any economic extrapolation into the distant future is at most an educated guess, likely to be quite wrong, with an expected error far in excess of 10%. (A rare example of a domain in which 75-year predictions are highly accurate is national demographic age charts, since the number of babies born this year in a given country is causal of the number of 75-year-olds alive in 75 years.)

The other joke of the title text is to call these “linear extrapolations.” They are actually ''exponential'', since a linear extrapolation on a graph with a logarithmic scale is actually an exponential extrapolation. The graph is log-linear, with price as a logarithmic scale on the vertical (left) axis, which makes it possible to visualize the exponential growth extrapolation as a straight line.

It’s unusual to plot commodity prices on a log-scale, but maybe Randall did this to allow himself to make this subtle “linear extrapolation” joke.

A statistically literate author would likely have plotted the same information using these best practices:
* normal linear axes
* using a range of potential long-term inflation rates illustrating various realistic scenarios (e.g., 1%, 2%, 3%, 5%, 10%)
* rephrasing the conclusion to say that the sitcom’s line might be obsolete in a century in a scenario in which long-term inflation is a very high average of 6%

This comic uses several common xkcd themes:
* '''Log scales''' and their peculiarities are a recurring xkcd theme, and this is the second comic in a row to play with logarithms (the prior one being [[2891: Log Cabin]]). 
* It's also the second comic in the last four to involve '''predictions across centuries''' (i.e. [[2889: Greenhouse Effect]]). 
* Another '''extrapolation''' comic include [[605: Extrapolating]]. And this comic looks a lot like [[1007: Sustainable]].

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

:[A graph with the x-axis showing time, from the years 1950 to around 2275. The y-axis is a log scale showing the price of a banana from $0.10 to over $10.00. A label called "Price of a banana (BLS/St. Louis ''Fred''[https://fred.stlouisfed.org/])" show a rising trend in the price of a banana. There are two dots on that trend. One is labeled "Episode airs" and the other one "Now". 3 extrapolations shown as dashed lines labeled "General inflation rate", "Fresh fruit price trend" and "Banana price trend" extend until reaching the $10 mark, indicated by 3 dots.]

:[Caption above the graph:] "It's one banana, Michael. What could it cost? $10?"

:[Caption below the panel:] That line probably has another century or so left.

{{comic discussion}}

[[Category:Line graphs]]
[[Category:Timelines]]
[[Category:Fiction]]
[[Category:Extrapolation]]