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	<title>Sentrana Blog &#187; modeling</title>
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	<description>Turning complexity into competitive advantage</description>
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		<title>Quantitative Intuition II: The Bayesian Brain&#8217;s Achilles Heel</title>
		<link>http://blog.sentrana.com/2009/07/02/quantitative-intuition-ii-the-bayesian-brains-achilles-heel/</link>
		<comments>http://blog.sentrana.com/2009/07/02/quantitative-intuition-ii-the-bayesian-brains-achilles-heel/#comments</comments>
		<pubDate>Thu, 02 Jul 2009 21:14:11 +0000</pubDate>
		<dc:creator>Katrina Lamb</dc:creator>
				<category><![CDATA[Modelers Mechanics]]></category>
		<category><![CDATA[Amos Tversky]]></category>
		<category><![CDATA[bayesian brain]]></category>
		<category><![CDATA[Bayesian theory]]></category>
		<category><![CDATA[behavioral economics]]></category>
		<category><![CDATA[Daniel Kahneman]]></category>
		<category><![CDATA[decision-making]]></category>
		<category><![CDATA[heuristic error]]></category>
		<category><![CDATA[heuristics]]></category>
		<category><![CDATA[human brain]]></category>
		<category><![CDATA[machine language]]></category>
		<category><![CDATA[modeling]]></category>
		<category><![CDATA[neuroscience]]></category>
		<category><![CDATA[quantitative methods]]></category>
		<category><![CDATA[sales & marketing]]></category>
		<category><![CDATA[scientific micromarketing]]></category>
		<category><![CDATA[uncertainty]]></category>

		<guid isPermaLink="false">http://blog.sentrana.com/?p=307</guid>
		<description><![CDATA[We humans make estimations and decisions based on likelihood and prior knowledge, an observation that has given rise to the notion of the "Bayesian brain".  But the elegance of our Bayesian reasoning is tripped up by our tendency to use heuristics to solve problems under conditions of uncertainty, leading to systematic, predictable errors.  Understanding and dealing with this mental Achilles heel is an important aspect in our continual efforts to integrate the best of the two worlds of quantitative methods and qualitative human judgment.]]></description>
			<content:encoded><![CDATA[<p>In a previous posting (<a href="http://blog.sentrana.com/2009/06/05/quantitative-intuition-its-not-counterintuitive-nor-an-oxymoron/" target="_self">“Quantitative Intuition: It’s Not Counterintuitive”</a>) I described some of the advancements that have been made in bringing together the disparate worlds of quantitative methods and human intuition, ending on the rather happy note that advanced scientific micromarketing models today are capable of introducing qualitative human judgment and experience into quantitative models, such that the models are able to “learn” from humans about important factors such as competitive threats, nuanced negotiation strategies and even meteorological vagaries – factors that traditionally have been difficult to crunch into the binary 1s and 0s of machine language.  The human brain works in a hierarchical manner, embedding propositions within propositions to think a potentially infinite number of thoughts.   In the example I used in the last posting, a sales rep who reads about a national wholesaler coming to town to open a discount distribution center can nearly instantaneously form a series of mental propositions to evaluate the importance of that news and the probability of potential outcomes that may (or may not) require decisive competitive action from the sales rep’s firm. <span id="more-307"></span></p>
<p>Looking at the human mind this way, as a machine constantly evaluating possible outcomes based on prior knowledge and assigning probability weights to those outcomes, gave rise to the notion of the “Bayesian brain,” a term popularized in 1983 by Geoffrey Hinton of the University of Toronto and Terry Sejnowski of Johns Hopkins University.  This notion has subsequently received a good amount of validation by neuroscientists as they continue to make advances in understanding how the brain really works.  Neuroscientists Alexandre Pouget and David Knill of the University of Rochester in 2004 referred to a “growing body of evidence that human perceptual computations are ‘Bayes optimal’ (“The Bayesian brain: the role of uncertainty in neural coding and computation,&#8221; <em>Trends in Neurosciences</em>, vol 27 issue 12, December 2004, pp 712-719).  That’s a fancy way of saying that we make estimations based on likelihood – for example we routinely make estimations about things like the distance from us of an object, or the speed at which it is traveling, based on our prior knowledge of the shape, clarity and movement patterns of such objects and the likelihood that the present reality fits into that a priori knowledge.</p>
<p>So far, so good.  But there is an Achilles heel to our hierarchical mental gymnastics.  Briefly, we may be great at the kind of proposition-within-proposition reasoning that our sales rep exhibited in getting to the essence of the competitive threat posed by the wholesaler’s move to town.  But we humans are generally pretty lame when it comes to computation.  Our intuitive reasoning skills fail at the task of instantaneously calculating that 34 x 57 X 71 = 137,598.  One way that we get around this failing is through heuristics – basically, shortcuts that we use in conditions of uncertainty to help us get from information to evaluation and decision.  Take the example above of evaluating the distance a particular object might be from us.  Now, there is a physics formula we could apply to measuring distance, height, momentum (if moving) and so forth to give us the precise answer as to how far away that bicyclist in the yellow jersey is from us.  But our brains lack the ability to do spontaneous physics equations.  Even if we precisely knew one or more of the variables it would be hard to do an on-the-spot computation.  So we need something else – a proxy, a heuristic.  That something might be clarity.  Can we see the bicyclist clearly?  Can we make out the details of his black helmet with red stripes, and the ‘Elf Aquitaine’ logo on the yellow jersey?  That can give us enough information to call upon our “cyclist in a yellow jersey” neuronal connections and infer a likelihood that he is, say, 50 yards away.</p>
<p>The problem with heuristics is that they are subject to error: not occasional lapses in judgment but systematic, predictable biases.  For example if we use clarity as a heuristic we may overestimate the distance of that cyclist from us if there is poor visibility.  Understanding the role of heuristic errors in human judgment and decision making was one of the main contributions of Amos Tversky and Daniel Kahneman to our understanding of behavioral factors in human decision-making (“Judgment Under Uncertainty: Heuristics and Biases,” Science New Series vol 185 no. 4157 Sep 1974 pp 1124-1131).  Tversky and Kahneman documented specific heuristic errors such as representativeness (drawing broad or sweeping conclusions from a limited data set), availability (assigning the likelihood of an event based on the easiest example that comes to mind, whether or not appropriate, and anchoring (relying heavily on one piece of information when making a decision even if it is irrelevant).</p>
<p>Since heuristic errors are part and parcel of human judgment and decision-making under uncertainty, we have to take this reality into account when we attempt to integrate quantitative modeling methods and qualitative human judgment.  What are the best mathematical tools and frameworks to integrate these two domains?  One area in which we at Sentrana are spending considerable time is that of Bayesian hierarchical modeling. The Bayesian approach is particularly useful in marketing situations such as modeling differences in the needs and wants of customers using both generalized and conditional assumptions involving multiple variables. Bayesian frameworks provide a natural way to pool disparate sources of information. A Bayesian model requires the formulation of prior distributions and the estimation of a likelihood function, which can add complexity to the model-building process.  However we expect future insights and innovations in this area, alongside the development of more robust computation capabilities to bring more firepower to bear on this difficult but potentially valuable quantitative approach.</p>
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		<title>In Economic Modeling, Can Hindsight Lead to Foresight?</title>
		<link>http://blog.sentrana.com/2009/04/21/in-economic-modeling-can-hindsight-lead-to-foresight/</link>
		<comments>http://blog.sentrana.com/2009/04/21/in-economic-modeling-can-hindsight-lead-to-foresight/#comments</comments>
		<pubDate>Tue, 21 Apr 2009 20:13:54 +0000</pubDate>
		<dc:creator>Katrina Lamb</dc:creator>
				<category><![CDATA[Modelers Mechanics]]></category>
		<category><![CDATA[19th century economics]]></category>
		<category><![CDATA[biology]]></category>
		<category><![CDATA[complex systems]]></category>
		<category><![CDATA[demand management]]></category>
		<category><![CDATA[economic modeling]]></category>
		<category><![CDATA[Eric D. Beinhocker]]></category>
		<category><![CDATA[John H. Miller]]></category>
		<category><![CDATA[Leon Walras]]></category>
		<category><![CDATA[modeling]]></category>
		<category><![CDATA[physics]]></category>
		<category><![CDATA[product mix]]></category>
		<category><![CDATA[scientific micromarket management]]></category>
		<category><![CDATA[Scott E. Page]]></category>
		<category><![CDATA[William Stanley Jevons]]></category>

		<guid isPermaLink="false">http://blog.sentrana.com/?p=147</guid>
		<description><![CDATA[Can the mistakes of hindsight lead to foresight when we approach the task of building economic models?  In other words, can we apply foresight to develop “good” economic models that won’t blow up in our faces?]]></description>
			<content:encoded><![CDATA[<p>In thinking more about my last posting here on <a title="You Cant Punt Away the Dimensionality Curse" href="http://blog.sentrana.com/2009/04/06/you-cant-punt-away-the-dimensionality-curse/" target="_blank">failed Wall Street quant models and the dimensionality curse</a> I started to wonder whether we could ever be more than the archetypal Monday morning quarterbacks:  commenting brilliantly on all the reasons why X should never have happened, after X has already happened and done its damage.  Can the mistakes of hindsight lead to foresight?  In other words, can we apply foresight to develop “good” economic models that won’t blow up in our faces?</p>
<p>In trying to answer this postulation we must go back to examine the eternal challenge of good modeling: how to create a simplified representation of reality that in ignoring many real-world features still manages to convey an inherently robust facsimile of the real thing.  For example, one of those maps of New England you buy at Exxon gas stations can serve as a good model for getting you from Hartford, CT to Boston, MA even if it ignores most of the streets and alleyways and other real-world detail that exist along the route.  In their book “Complex Adaptive Systems: An Introduction to Computational Models of Social Life” John H. Miller and Scott E. Page observe that the “ability to ignore is a crucial component of scientific progress”, using the image of a parent’s being able to respond to the incessant “why” questions of a three year old child by saying “just because”.  The trick, as the authors point out, is knowing when (and perhaps more importantly when not) to say “just because”.</p>
<p>While I wholeheartedly agree with that assertion I don’t think that it quite gets us to an adequate level of comfort in applying foresight to the creation of good models.  In his fascinating book “The Origin of Wealth” Eric D. Beinhocker points out that economic modeling took what many consider to be a wrong turn back in the latter years of the 19th century when leading thinkers of the day like Leon Walras and William Stanley Jevons borrowed heavily from the referential context of physics to create models for explaining economic activity, including such notable concepts as a mathematically representable state of equilibrium that continue to serve as the conceptual foundations of modern economics textbooks.  As Beinhocker elaborates, the problem with these models was that some of their fundamental assumptions – like the perfect, robot-like rationality of human beings in making economic choices – didn’t seem to simplify reality as much as contradict reality.  Thus we find ourselves in the present ruminating over the precise, mathematically elegant language of physics and the complex, evolutionary language of biology and debating whether a choice of the wrong science by the founding fathers of economics back in the 19th century led to the failure of models to adequately explain much of what is going on in the economy today and in particular the string of boom-bust upheavals that have become part and parcel of the last 20-odd years of economic activity.</p>
<p>I still don’t think we are there yet in getting closure on the foresight question, but we may be getting closer.  To tie in the strands of thought presented by Miller &amp; Page and Beinhocker, when we get to those basic defining assumptions,<span id="more-147"></span> when we decide what the model is going to ignore and what it is going to retain, when we say “just because”, that is the point where we have the chance to either build a robust foundation that can withstand the slings and arrows of a continual barrage of economic X-factors or an elegant, commercially viable sandcastle that gets washed away with the next high tide.  If we are going to apply foresight, this is where we have to apply it.</p>
<p>Not that applying foresight is easy, of course, and that is why at Sentrana we are engaged in a continual process of building better models by going back to the basics, asking seemingly simple questions that have complex answers, and trying to ensure that we get it right when we get to that point where it is time to say “just because”.  In our world of Scientific Micromarket Management saying “just because” at the right time can, for example, open up the vista of a complex demand environment to reveal a unique configuration of product mix opportunities at optimal pricing points.  It’s good that we are seeing a heightened level of public discourse about these issues: models may seem to be abstract notions for abstemious minds, but they have real-world economic consequences.  Getting it right has never been more important.</p>
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