Post Hoc Ergo Propter Hoc

We decided a few months ago to replace the wallpaper in our dining room. It was very outdated, and with the holidays approaching, we thought it would be a nice touch, sort of liven up the room when everyone was over for Christmas dinner. We’re very much the DIY type, so we spent a few after-work evenings peeling the old paper off. Once we were done and the walls were prepped, we went to Home Depot (for the third or fourth time) to make the final decision on which wallpaper we wanted to hang. It was at the point that I realized we really had no clue how much we needed. Then I remembered my friend Sylvia had recently done basically the same project. I called her from Home Depot.

“Yes,” she answered, “as a matter of fact, I did.”

“Your dining room isn’t much bigger than ours – how much paper did you end up buying?” I wanted to know.

She thought for a moment. “Seven rolls is what I ended up getting.”

We bought seven rolls of wallpaper, and spent the next two weekends watching YouTube videos and hanging wallpaper. Oddly, we ended up with four unused rolls, and started to think we had done something very wrong. I immediately called Sylvia.

“Hey, I’m not sure if we did this right,” I said. “We ended up with four rolls left over…”

“Oh, how weird, “she replied, “that happened to you, too?”

Data is an important thing, but sometimes – all of the time, actually – it is more important how you utilize that data. I asked a specific question, Sylvia provided a specific answer to my specific question. I didn’t think to question the data she was providing, and having answered my question precisely, she didn’t think to qualify her response with something like, “…but we only used four of the rolls.”

The common logical fallacy post hoc, ergo propter hoc – literally “after this, therefore because of this” – comes to mind. She purchased seven rolls of wallpaper and completed her project successfully, therefore I jumped to the conclusion that seven rolls of wallpaper were needed for our project as well. Had I stopped to question that – or better, had I rephrased my question slightly – I wouldn’t have been stuck with four extra rolls of wallpaper. Had I asked her, for example, “How many rolls did you need to paper your dining room?”, I probably wound’t have had to make yet another trip to Home Depot to return the excess wallpaper.

Had I just refined my parameters slightly, I could have very easily turned my data (facts and figures) into information (structured, meaningful data). It really is just that simple. By merely thinking ahead slightly and understanding what I was trying to accomplish, the outcome would have been more advantageous.

Now, four rolls of wallpaper doesn’t seem like much, but what if I’d wanted to re-paper my entire house? Or, to extend this to the work environment, what if I wanted to replenish my stock of very expensive radio modems? I might ask, “How many modems did we order last time?” The answer may be 100, but what were the circumstances of that order. Was it a routine replenishment? Or were we filling a specific customer order? Do I really need to order \$50,000 worth of hardware, or will that put me in the position of having to unload them at a reduced price because suddenly technology has changed and these modems are no longer viable in the marketplace?

Which reminds me of another story…

A close friend of ours recently received the sad news from her physician that she had contracted a debilitating illness and had only six months left to live. Being a very matter-of-fact person, she took the news with considerable aplomb, and asked her doctor, “Is there anything I can do?”

The doctor considered her question, then replied, “Well, actually, there is. You could marry a cost accountant.”

She looked at the physician skeptically and asked, “But how will that help my illness?”