Nate Silver is one of those rare researchers with the uncanny ability to send your brain spinning off on unintended tangents totally unrelated to the work he’s actually documenting. His work is fascinating more for its process than its conclusions, and often generates new introspections applicable to our own areas of expertise. Take this article in Esquire where he discusses the concept of recency bias as applied to financial risk assessments.
Recency bias is the tendency to skew data and analysis towards recent events. In the economic example he uses he compares the risk of a market crash in 2008 using data from the past 60 years vs. the past 20. The difference is staggering; from one major downturn every 8 years 
(using 60 years of data) vs. a downturn every 624 years (using only 20 years of data). As with all algorithms, input selection deeply skews output results, with the potential for cataclysmic conclusions.
In the information security industry I believe we just as frequently suffer from selective inverse recency bias- giving greater credence to historical data over more recent information, while editing out the anomalous events that should drive our analysis more than the steady state. Actually, I take that back, it isn’t just information security, but safety and security in general, and it is likely of a deep evolutionary psychological origin. We cut out the bits and pieces we don’t like, while pretending the world isn’t changing.
Here’s what I mean- in security we often tend to assume that what’s worked in the past will continue to work in the future, even though the operating environment around us has completely changed. At the same time, we allow recency bias to intrude and selectively edit out our memories of negative incidents after some arbitrary time period. We assume what we’ve always done will always work, forgetting all those times it didn’t work.
From an evolutionary psychology point of view (assuming you go in for that sort of thing) this makes perfect sense. For most of human history what worked for the past 10, 20, or 100 years still worked well for the next 10, 20, or 100 years. It’s only relatively recently that the rate of change in society (our operating environment) accelerated to high levels of fluctuation in a single human lifetime. On the opposite side, we’ve likely evolved to overreact to short term threats over long term risks- I doubt many of our ancestors were the ones contemplating the best reaction to the tiger stalking them in the woods; our ancestors clearly got their asses out of there at least fast enough to procreate at some point.
We tend to ignore long term risks and environmental shifts, then overreact to short term incidents.
This is fairly pronounced in information security where we need to carefully balance historical data with our current environment. Over the long haul we can’t forget historical incidents, yet we also can’t assume that what worked yesterday will work tomorrow.
It’s important to use the right historical data in general, and more recent data in specific. For example, we know major shifts in technology lead to major new security threats. We know that no matter how secure we feel, incidents still occur. We know that human behavior doesn’t change, people will make mistakes, and are predictably unpredictable.
On the other hand, firewalls only stop a fraction of the threats we face, application security is now just as important as network security, and successful malware utilizes new distribution channels and propagation vectors.
Security is always a game of balance. We need to account for the past, without assuming its details are useful when defending against specific future threats.
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