POST HOC ERGO PROPTER HOC

Welcome to today’s Latin lesson. “Post hoc ergo propter hoc” means “after it, therefore because of it”. It is the title of a West Wing episode from Season 1 (and you can watch the scene herewhere it is discussed). It also happens to be the sort of thing they teach you if you study logic and comes in handy if you love data and helping organizations improve services.

In a nutshell, you can write up the formula like this:

  • X happened, then Y happened
  • Therefore, X caused Y

You can also have people reverse elements of the equation. Let’s say it really sucks for Y to happen. In that case, if you avoid or prevent X then Y won’t occur.

If you look just at the order of events rather than the influences on the events you can draw oodles of false conclusions. A temporal succession of events is not evidence of a causal relation. Does a rooster raising a cacophony just before the sun rises cause the sun to rise?

A lot of times when engaged with people, there is a reliance on anecdotes to explain causation rather than examining influences independently. The problem with anecdotes (amongst many) is that they are open to subjective interpretation, have the bias of the anecdote teller, rely considerably on intuition and frequently ask the listener to believe based upon the existing relationship between anecdote-teller and anecdote-listener rather than facts.

For those of you who love to support or play sports, you know that there is a lot of superstitions that occur which fall victim to post hoc ergo propter hoc thinking. As a species we are in search for meaning. We use superstition to sometimes create explanations for things simply rather than looking at other factors that may have had an influence. Was it really putting on the yellow headband before the tennis match that made her win? Maybe it was that the headband kept the hair out of her eyes. Or maybe it was nothing to do with her headband…that her opponent was under the weather…or that she had trained hard on her serve and footwork…or the match started with the wind at her back…and so on. To state that putting on the yellow headband before the match that she won caused her to win the match just doesn’t cut it.

Key messaging from a public relations perspective frequently falls victim to post hoc ergo propter hoc thinking. In one community recently I heard the following statement from a local elected official, “Since 2002 when we opened the [name of facility withheld] homelessness has dropped 11.78%.”

It begs a lot of questions. What has happened in the local economy over the same period of time? The community was at double digits of unemployment when the facility opened but steadily declined even through the recession. What about the more steady and rapid decline in homelessness after the 10 Year Plan and new programming were introduced in 2007? What about the investments in professional development for staff in the community to the tune of almost $200,000 in the past three years to learn better strategies to help people access and maintain housing? What about the availability of more rent subsidies available since 2008? So, did the facility opening cause the drop in homelessness? It may be part of the equation depending on who the facility caters to and the programs operated out of the facility, but unless you look at the whole picture you can’t say that the drop in homelessness after the facility being opened caused the drop in homelessness. (And as an aside, always exercise caution in Human Services data analysis which goes to a second decimal place…people are trying to baffle you with precision when the precision is not warranted given the margin of error accepted and expected in this type of analysis and research.)

And let’s take a moment to examine the reverse of the formula…that if you prevent X from happening then Y won’t happen. Complex social issues tend to have more than one factor that needs to be considered. For example, homelessness is rarely caused by one event…it is the manifestation of several events over time (where sequence may be irrelevant) that destabilizes housing or the confluence of multiple factors during a single event. A reduction of focus to just one factor tries to over-simplify prevention activities and will likely result in more anecdotes than proof when trying to explain your efforts to prevent homelessness. (Look at this another way – we know lots about risk factors for homelessness and prevalent characteristics of chronically homeless people and families, yet to this day do not have a full-proof way of preventing homelessness because the cause and effect cannot be easily traced and applied to the unique circumstances of different households.)

In Human Services in particular – although applicable to any organization with inter-personal interaction – I strongly urge people to look for meaning and explanation beyond just the sequence of events. Dig deeper. Look at context. Examine a range of rational factors that may have had an influence. Then draw together the plausible narrative of why things are the way that they are.

About Iain De Jong

Iain is a playful nerd, hellbent on ending homelessness, increasing affordable housing, creating vibrant communities, and expanding the knowledge amongst leaders that influence social issues. Having held senior management and professional positions in government, non-profits, and the private sector, Iain has a wealth of experience and has garnered dozens of awards for his work across Canada and internationally. His work has taken him across Canada, the United States, and to Australia. In 2009, Iain joined OrgCode as its President & CEO, and in 2014 assumed full ownership of the firm. In addition to his work with OrgCode, Iain holds a part-time faculty position in the Graduate Urban Planning Programme at York University.


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