Cohort and Age Effects
Cohort and Age Effects
[Cueball as a news anchor is sitting at a desk with hands folded in front of him on the table.] Cueball: Tonight: Are Millennials killing the joint replacement industry?

[To the left of Cueball is a presentation which includes a two by two table with a header above the table. Each of the two rows and columns are labeled, with rows entitled 'Baby Boomers' and  'Millennials', and columns entitled 'Knee' and 'Hip']
Operation rate per 100,000 Baby Boomers: Knee: 720 Hip: 390 Millennials: Knee: 1 Hip: 3

[Caption below the panel:] Stats Pet Peeve: People mixing up cohort effects and age effects.

Another of Randall's many Pet Peeves , this time it's statistics. It is the first in more than four years, since 1368: One Of The .
" Millennials " are the generation of Westerners who were born between the early 1980s and the late 1990s, whereas baby boomers are the generation born during the "baby boom", a period of high birth rates from the late 1940s to early 1960s. A common headline on news websites is "Millennials are killing the X industry" where X is a product whose sales have dropped in recent years, such as jungle gyms for kids . One of the most famous is the diamond industry , where a combination of the wage gap , stigma over conflict diamonds , increased knowledge of ( in Randall's words ) "complicated gemstone market" and less desire to get married early has seen millennials buying less diamond jewelry than previous generations.
Randall spoofs this idea. In the comic, Cueball , as a news anchor , presents a heading which opens his story by asking if millennials are killing the industry of surgical joint replacements , illustrating it with numbers of joint replacement procedures among millennials compared to baby boomers. The joke is that millennials are simply too young for most of them to need joint replacements (which are usually used to treat senile osteoarthritis ), so most people will see that so there really isn't a news story here. Randall is using this example to highlight that this kind of story is ridiculous. Millennials will likely need joint replacements in the future as they get older, potentially keeping sales of joint replacements at close to their current rate.
A cohort effect is a cultural difference between generations (such as buying fewer diamonds), whereas an age effect is one that is simply related to getting older (such as getting arthritis). Joint replacement rates are an age effect, but the newscast is presenting them as if they were a cohort effect. (More correctly, the table rows would be labelled e.g. “people aged 50–70” and “people aged 22–37”.)
The title text points out that although numbers of millennials receiving joint replacements are low, they are higher than the numbers of baby boomers who received them at the same age —i.e. in their 20s—due to advances in medical diagnosis and technology in the last 50 years, as well as (in some countries at least) better access to healthcare. This statistic can be used to create a headline which is the reverse of the one in the comic, namely "millennials are getting more joint replacements than ever". Randall notes that you could therefore use either headline to back up your argument, depending on the agenda you are trying to present.
[Cueball as a news anchor is sitting at a desk with hands folded in front of him on the table.] Cueball: Tonight: Are Millennials killing the joint replacement industry?

[To the left of Cueball is a presentation which includes a two by two table with a header above the table. Each of the two rows and columns are labeled, with rows entitled 'Baby Boomers' and  'Millennials', and columns entitled 'Knee' and 'Hip']
Operation rate per 100,000 Baby Boomers: Knee: 720 Hip: 390 Millennials: Knee: 1 Hip: 3

[Caption below the panel:] Stats Pet Peeve: People mixing up cohort effects and age effects.
