### The Two Cultures: statistics vs. machine learning?

Last year, I read a blog post from Brendan O'Connor entitled "Statistics vs. Machine Learning, fight!" that discussed some of the differences between the two fields. Andrew Gelman responded favorably to this:

Simon Blomberg:

From R's fortunes package: To paraphrase provocatively, 'machine learning is statistics minus any checking of models and assumptions'. -- Brian D. Ripley (about the difference between machine learning and statistics) useR! 2004, Vienna (May 2004) :-) Season's Greetings!

Andrew Gelman:

In that case, maybe we should get rid of checking of models and assumptions more often. Then maybe we'd be able to solve some of the problems that the machine learning people can solve but we can't!

There was also the

**"Statistical Modeling: The Two Cultures"**paper by Leo Breiman in 2001 which argued that statisticians rely too heavily on data modeling, and that machine learning techniques are making progress by instead relying on the*predictive accuracy*of models.Has the statistics field changed over the last decade in response to these critiques? Do the

*two cultures*still exist or has statistics grown to embrace machine learning techniques such as neural networks and support vector machines?Add a third culture: **data mining**. Machine learners and data miners speak quite different languages. Usually, the machine learners don't even understand what is different in data mining. To them, it's just unsupervised learning; they ignore the data management aspects and apply the *buzzword* data mining to machine learning, too, adding further to the confusion.

There's a similar question on data mining and statistics

An interesting discussion in Wasserman's blog.

My two cents: *Can you check a cross-validated classification accuracy for significant deviation from chance using a binomial test?* The extremely useful technique of cross-validation is usually attributed to machine learning. But checking its properties is a job left to people concerned with statistics...

My two cents: Using an analogy drawn from the field of mathematics: Machine Learning is to *Applied Mathematics*, what Statistics is to *Pure Mathematics*

As of now, the word _machine learning_, not the underlying process, is pretty much a buzzword itself. _Machine assisted learning_ would probably be a more accurate title for the process but it lacks the coolness factor of the former.

It seems to me that actually the link between ML and statistics is not being emphasized enough. Many CS students ignore learning anything about statistics during their foundational days because they don't understand the critical importance of a sound statistics grounding in carrying out ML tasks. Maybe even a lot of CS departments around the world would be slow to act as well. It would prove to be very costly mistake and I certainly hope there's more awareness about the importance of statistics knowledge in CS. Basically ML = Statistics in a lot of senses.

Another great paper, "To Explain or Predict" https://www.stat.berkeley.edu/~aldous/157/Papers/shmueli.pdf

See also this question on our Operations Research website.

I think the answer to your first question is simply in the affirmative. Take any issue of Statistical Science, JASA, Annals of Statistics of the past 10 years and you'll find papers on boosting, SVM, and neural networks, although this area is less active now. Statisticians have appropriated the work of Valiant and Vapnik, but on the other side, computer scientists have absorbed the work of Donoho and Talagrand. I don't think there is much difference in scope and methods any more. I have never bought Breiman's argument that CS people were only interested in minimizing loss using whatever works. That view was heavily influenced by his participation in Neural Networks conferences and his consulting work; but PAC, SVMs, Boosting have all solid foundations. And today, unlike 2001, Statistics is more concerned with finite-sample properties, algorithms and massive datasets.

But I think that there are still three important differences that are not going away soon.

- Methodological Statistics papers are still overwhelmingly formal and deductive, whereas Machine Learning researchers are more tolerant of new approaches even if they don't come with a proof attached;
- The ML community primarily shares new results and publications in conferences and related proceedings, whereas statisticians use journal papers. This slows down progress in Statistics and identification of star researchers. John Langford has a nice post on the subject from a while back;
- Statistics still covers areas that are (for now) of little concern to ML, such as survey design, sampling, industrial Statistics etc.

Great post! Note that Vapnick had a PhD in statistics. I'm not sure there are a lot of computer scientist that know the name Talagrand and I'm sure 0.01% of them can state by memory one result of talagrand :) can you ? I don't know the work of Valiant :)

I see the different answers when it comes to academic research and applications. I think that you answered in the context of the former. In applications I think the biggest difference is in the way the fields are expanding. ML through data science channel accepts everyone who can code, literally. In statistics you still need a formal degree in stats or near fields to enter the work force.

Both survey sampling and industrial statistics are multi-billion dollar fields (survey research methods section of the American Statistical Association is the third largest after biometrics and consulting, and the latter includes a great number of industrial statisticians, too. There's a separate section on quality, and there is a yet separate Six-Sigma stuff and other quality control methods out there, not all of them entirely in statsitics). Both have critical shortages of statisticians as the current workforce of baby boomers who came to work in these areas in the 1960s is retiring.

While some people get their jobs by posing on the red carpet at conferences, other people find theirs by applying the methods in the real world. The latter folks don't have *that* much interest in identifying the stars of any kind; they would rather much identify the methods that work, although on many occasions, after a few years in a given field, you are led to the same names over and over again.

Why would sampling not be of concern to ML? Isn't that quite similar to the problem of having the right labelled training data in ML?

The biggest difference I see between the communities is that statistics emphasizes inference, whereas machine learning emphasized prediction. When you do statistics, you want to infer

*the process by which data you have was generated.*When you do machine learning, you want to know how you can*predict what future data will look like w.r.t. some variable.*Of course the two overlap. Knowing how the data was generated will give you some hints about what a good predictor would be, for example. However, one example of the difference is that machine learning has dealt with the p >> n problem (more features/variables than training samples) since its infancy, whereas statistics is just starting to get serious about this problem. Why? Because you can still make good predictions when p >> n, but you can't make very good inferences about what variables are actually important and why.

Could this be (overly) simplified as something like the difference between generative and discriminative models?

@Wayne: Yeah, I think this is actually a pretty fair way of putting it.

"One should solve the [classification] problem directly and never solve a more general problem as an intermediate step..." - Vapnik

I disagree that no inference can be done with ML; one can squeeze quite a lot from importance scores some methods produce and/or some feature selection schemes.

@mbq: I didn't mean to imply that no inference can be done, just that it's not the main goal and that usually p >> n in ML, making it a lot harder.

I agree 100% with this view. ML focuses on prediction because it was meant to automate pattern recognition in software systems. As a result, ML methods are nonparametric and black box.

Still a lot of work to do in machine learning if you want to do something like, say, model the full probability distribution of a set of unknown, highly structured parameters, then use that model to make posterior predictions about the full distribution, not point estimates of new data. You can do the latter with boosted quantile regression. You can do the former with some new random effects flavored random forest models. Can't find anything that does both at the same time. BUT machine learning methods very useful to help define the structure of a (semi)parametric model & predictors to include

(As an example, I used variable importance measures from a colleague's random forest model to inform a multilevel modeling and post-stratification procedure to build a model of the the probability distribution of some very noisy transaction data.)

I strongly disagree with this view. It looks wrong. Things like recurrent neural networks also try to infer processes, and even go on and generate new sequences.

So what about robotics? Probabilistic robotics is largely focused on inference, and pretty dominant in applications. But still a different "flavor" than statistics (and more engineering compared to machine/learning; i.e. real-time analysis/control)

Doesn't Bayesian statistics coherently integrate prediction (e.g. $p(\tilde{y}|y)$ within its framwework (cf. BDA3 by Gelman for example)? If so, then this answer likely must be read with the premise *"Bayesian stats are not (regular) statistics"* to make it a true one?

Bayesian: "Hello, Machine Learner!"

Frequentist: "Hello, Machine Learner!"

Machine Learning: "I hear you guys are good at stuff. Here's some data."

F: "Yes, let's write down a model and then calculate the MLE."

B: "Hey, F, that's not what you told me yesterday! I had some univariate data and I wanted to estimate the variance, and I calculated the MLE. Then you pounced on me and told me to divide by $n-1$ instead of by $n$."

F: "Ah yes, thanks for reminding me. I often think that I'm supposed to use the MLE for everything, but I'm interested in unbiased estimators and so on."

ML: "Eh, what's this philosophizing about? Will it help me?"

F: " OK, an

*estimator*is a black box, you put data in and it gives you some numbers out. We frequentists don't care about how the box was constructed, about what principles were used to design it. For example, I don't know how to derive the $\div(n-1)$ rule."ML: " So, what do you care about?"

F: "Evaluation."

ML: "I like the sound of that."

F: "A black box is a black box. If somebody claims a particular estimator is an unbiased estimator for $\theta$, then we try many values of $\theta$ in turn, generate many samples from each based on some assumed model, push them through the estimator, and find the average

*estimated $\theta$*. If we can prove that the expected estimate equals the true value, for all values, then we say it's unbiased."ML: "Sounds great! It sounds like frequentists are pragmatic people. You judge each black box by its results. Evaluation is key."

F: "Indeed! I understand you guys take a similar approach. Cross-validation, or something? But that sounds messy to me."

ML: "Messy?"

F: "The idea of testing your estimator on real data seems dangerous to me. The empirical data you use might have all sorts of problems with it, and might not behave according the model we agreed upon for evaluation."

ML: "What? I thought you said you'd proved some results? That your estimator would always be unbiased, for all $\theta$."

F: "Yes. While your method might have worked on one dataset (the dataset with train and test data) that you used in your evaluation, I can prove that mine will always work."

ML: "For all datasets?"

F: "No."

ML: "So my method has been cross-validated on one dataset. You haven't test yours on any real dataset?"

F: "That's right."

ML: "That puts me in the lead then! My method is better than yours. It predicts cancer 90% of the time. Your 'proof' is only valid if the entire dataset behaves according to the model you assumed."

F: "Emm, yeah, I suppose."

ML: "And that interval has 95%

*coverage*. But I shouldn't be surprised if it only contains the correct value of $\theta$ 20% of the time?"F: "That's right. Unless the data is truly i.i.d Normal (or whatever), my proof is useless."

ML: "So my evaluation is more trustworthy and comprehensive? It only works on the datasets I've tried so far, but at least they're real datasets, warts and all. There you were, trying to claim you were more 'conservative' and 'thorough' and that you were interested in model-checking and stuff."

B: (interjects) "Hey guys, Sorry to interrupt. I'd love to step in and balance things up, perhaps demonstrating some other issues, but I really love watching my frequentist colleague squirm."

F: "Woah!"

ML: "OK, children. It was all about evaluation. An estimator is a black box. Data goes in, data comes out. We approve, or disapprove, of an estimator based on how it performs under evaluation. We don't care about the 'recipe' or 'design principles' that are used."

F: "Yes. But we have very different ideas about which evaluations are important. ML will do train-and-test on real data. Whereas I will do an evaluation that is more general (because it involves a broadly-applicable proof) and also more limited (because I don't know if your dataset is actually drawn from the modelling assumptions I use while designing my evaluation.)"

ML: "What evaluation do you use, B?"

F: (interjects) "Hey. Don't make me laugh. He doesn't evaluate anything. He just uses his subjective beliefs and runs with it. Or something."

B: "That's the common interpretation. But it's also possible to define Bayesianism by the evaluations preferred. Then we can use the idea that none of us care what's in the black box, we care only about different ways to evaluate."

B continues: "Classic example: Medical test. The result of the blood test is either Positive or Negative. A frequentist will be interested in, of the Healthy people, what proportion get a Negative result. And similarly, what proportion of Sick people will get a Positive. The frequentist will calculate these for each blood testing method that's under consideration and then recommend that we use the test that got the best pair of scores."

F: "Exactly. What more could you want?"

B: "What about those individuals that got a Positive test result? They will want to know 'of those that get a Positive result, how many will get Sick?' and 'of those that get a Negative result, how many are Healthy?' "

ML: "Ah yes, that seems like a better pair of questions to ask."

F: "HERESY!"

B: "Here we go again. He doesn't like where this is going."

ML: "This is about 'priors', isn't it?"

F: "EVIL".

B: "Anyway, yes, you're right ML. In order to calculate the proportion of Positive-result people that are Sick you must do one of two things. One option is to run the tests on lots of people and just observe the relevant proportions. How many of those people go on to die of the disease, for example."

ML: "That sounds like what I do. Use train-and-test."

B: "But you can calculate these numbers in advance, if you are willing to make an assumption about the rate of Sickness in the population. The frequentist also makes his calcuations in advance, but without using this population-level Sickness rate."

F: "MORE UNFOUNDED ASSUMPTIONS."

B: "Oh shut up. Earlier, you were found out. ML discovered that you are just as fond of unfounded assumptions as anyone. Your 'proven' coverage probabilities won't stack up in the real world unless all your assumptions stand up. Why is my prior assumption so diffent? You call me crazy, yet you pretend your assumptions are the work of a conservative, solid, assumption-free analysis."

B (continues): "Anyway, ML, as I was saying. Bayesians like a different kind of evaluation. We are more interested in conditioning on the observed data, and calculating the accuracy of our estimator accordingly. We cannot perform this

*evaluation*without using a prior. But the interesting thing is that, once we decide on this form of evaluation, and once we choose our prior, we have an automatic 'recipe' to create an appropriate estimator. The frequentist has no such recipe. If he wants an unbiased estimator for a complex model, he doesn't have any automated way to build a suitable estimator."ML: "And you do? You can automatically build an estimator?"

B: "Yes. I don't have an automatic way to create an unbiased estimator, because I think bias is a bad way to evaluate an estimator. But given the conditional-on-data estimation that I like, and the prior, I can connect the prior and the likelihood to give me the estimator."

ML: "So anyway, let's recap. We all have different ways to evaluate our methods, and we'll probably never agree on which methods are best."

B: "Well, that's not fair. We could mix and match them. If any of us have good labelled training data, we should probably test against it. And generally we all should test as many assumptions as we can. And some 'frequentist' proofs might be fun too, predicting the performance under some presumed model of data generation."

F: "Yeah guys. Let's be pragmatic about evaluation. And actually, I'll stop obsessing over infinite-sample properties. I've been asking the scientists to give me an infinite sample, but they still haven't done so. It's time for me to focus again on finite samples."

ML: "So, we just have one last question. We've argued a lot about how to

*evaluate*our methods, but how do we*create*our methods."B: "Ah. As I was getting at earlier, we Bayesians have the more powerful general method. It might be complicated, but we can always write some sort of algorithm (maybe a naive form of MCMC) that will sample from our posterior."

F(interjects): "But it might have bias."

B: "So might your methods. Need I remind you that the MLE is often biased? Sometimes, you have great difficulty finding unbiased estimators, and even when you do you have a stupid estimator (for some really complex model) that will say the variance is negative. And you call that unbiased. Unbiased, yes. But useful, no!"

ML: "OK guys. You're ranting again. Let me ask you a question, F. Have you ever compared the bias of your method with the bias of B's method, when you've both worked on the same problem?"

F: "Yes. In fact, I hate to admit it, but B's approach sometimes has lower bias and MSE than my estimator!"

ML: "The lesson here is that, while we disagree a little on evaluation, none of us has a monopoly on how to create estimator that have properties we want."

B: "Yes, we should read each other's work a bit more. We can give each other inspiration for estimators. We might find that other's estimators work great, out-of-the-box, on our own problems."

F: "And I should stop obsessing about bias. An unbiased estimator might have ridiculous variance. I suppose all of us have to 'take responsibility' for the choices we make in how we evaluate and the properties we wish to see in our estimators. We can't hind behind a philosophy. Try all the evaluations you can. And I will keep sneaking a look at the Bayesian literature to get new ideas for estimators!"

B:"In fact, a lot of people don't really know what their own philosophy is. I'm not even sure myself. If I use a Bayesian recipe, and then proof some nice theoretical result, doesn't that mean I'm a frequentist? A frequentist cares about above proofs about performance, he doesn't care about recipes. And if I do some train-and-test instead (or as well), does that mean I'm a machine-learner?"

ML: "It seems we're all pretty similar then."

For readers who will read this response to the end I would suggest to add a brief take-away message (and to provide appropriate citation if it applies).

With -2 votes so far, I think there's not much I can do to save it :) I think the ending, where they all agree with each other, and admit they can use each others methods without worry about each others philosophy, is a 'take-away message'.

No citation required. I just made it up myself. It's probably not very well informed, it's based on my own (mis)-interpretations of arguments I've had with a small number of colleagues over the years.

I've seen such dialogue (shorter, though) in the past, and I find them interesting. I was also concerned by the downvotes, hence my suggestion to put a brief summary at the top so as to motivate readers to read the rest of your post.

@chi, Interesting. Maybe I'll stop worrying about the downvotes, and just work on improving it! But not just yet.

13/10 would argue again

Congratulations to the author, really informative and fun read.

abysmal. ${}{}{}$

In such a discussion, I always recall the famous Ken Thompson quote

When in doubt, use brute force.

In this case, machine learning is a salvation when the assumptions are hard to catch; or at least it is much better than guessing them wrong.

With the increased computational capabilities these years and autoencoders and associated techniques, this is more true than ever.

To solve a problem ,engineers use formulas , techniques and procedures , which they have used before and are sure of their success...Ordinarily , it is called the use Brute Force or the use of Thumb Rules ...New formulas ,techniques and procedures are used in a step by step process ...Engineering activities are group activities --where Engineers , Technicians and manual Laborers work together . When a new procedure is introduced , it takes time to train the Technicians and Laborers with this procedure . So modernisation is introduced in an Evolutionary process.

What enforces more separation than there should be is each discipline's lexicon.

There are many instances where ML uses one term and Statistics uses a different term--but both refer to the same thing--fine, you would expect that, and it doesn't cause any permanent confusion (e.g., features/attributes versus expectation variables, or neural network/MLP versus projection-pursuit).

What's much more troublesome is that both disciplines use the same term to refer to completely different concepts.

A few examples:

*Kernel Function*In ML, kernel functions are used in classifiers (e.g., SVM) and of course in kernel machines. The term refers to a simple function (

*cosine, sigmoidal, rbf, polynomial*) to map non-linearly separable to a new input space, so that the data is now linearly separable in this new input space. (versus using a non-linear model to begin with).In statistics, a kernel function is weighting function used in density estimation to smooth the density curve.

*Regression*In ML, predictive algorithms, or implementations of those algorithms that return class labels "classifiers" are (sometimes) referred to as

--e.g.,*machines**support vector machine*,*kernel machine*. The counterpart to machines are*regressors*, which return a*score*(continuous variable)--e.g.,*support vector regression*.Rarely do the algorithms have different names based on mode--e.g., a MLP is the term used whether it returns a class label or a continuous variable.

In Statistics,

*regression*, if you are attempting to build a model based on empirical data, to predict some response variable based on one or more explanatory variables or more variables--then you are doing*regression*analysis. It doesn't matter whether the output is a continuous variable or a class label (e.g., logistic regression). So for instance, least-squares regression refers to a model that returns a continuous value; logistic regression on the other hand, returns a probability estimate which is then discretized to a class labels.*Bias*In ML, the

*bias*term in the algorithm is conceptually identical to the*intercept*term used by statisticians in regression modeling.In Statistics, bias is non-random error--i.e., some phenomenon influenced the entire data set in the same direction, which in turn means that this kind of error cannot be removed by resampling or increasing the sample size.

In statistics, bias is not the same as error. Error is purely random, bias is not. You have bias when you know that the expected value of your estimate is not equal to the true value.

(@Joris Or even if you don't know it! Sounds trite, but just figuring out if there's bias can be a considerable practical problem. From the data alone, how sure can you be that an estimated regression parameter is free of omitted variable bias?) It's a common misconception that bias is a feature of the data, not a property of an estimator; I wonder if it stems from non-technical usage like "that survey is biased!" Statisticians also aren't always consistent about terms like "error": mean square error (of an estimator) includes a bias-squared component, so that "error" isn't "purely random".

I think the term "machine" in SVMs should be attributed to the personal taste of Vladimir Vapnic. Nowadays, I don't think it is not used to name any other classifier.

Many of these aren't consistent with the usage I've seen in the ML community. Both types of kernels are in wide use (though Hilbert space kernels being more common), "machine" is basically only used for SVMs (as iliasfl notes), and "bias" usually means $\mathbb{E}[\hat{X} - X]$ (perhaps conditioned on something) which is not the same thing as an intercept.

The statement "logistic regression on the other hand, returns a class labels." is wrong. Logistic regression returns continues values in $[0, 1]$ that are estimates for the probability to belong to the class coded as $1$.

"logistic regression on the other hand, returns a class labels": that isn't quite right is it? Logistic regression returns probability estimates, not labels. EDIT: I see someone said the same thing.

Also, never heard the *machine* argument. In ML there's classification, regression, clustering, etc. The learners are just that, learners, and are apt for different tasks. In general, only SVMs are related algorithms (LSSVM, RVM, IVM, TSVM, etc) are called *machines*.

The largest differences I've been noticing in the past year are:

- Machine learning experts do not spend enough time on fundamentals, and many of them do not understand optimal decision making and proper accuracy scoring rules. They do not understand that predictive methods that make no assumptions require larger sample sizes than those that do.
- We statisticians spend too little time learning good programming practice and new computational languages. We are too slow to change when it comes to computing and adopting new methods from the statistical literature.

Another note is that us statisticians tend to limit ourselves to methods we can prove with math that will work well (under a set of maybe ridiculous assumptions), especially when it comes to publications. Machine learning people are very happy to use methods that empirically work well on a few datasets. As a result, I think the ML literature moves much faster but also requires more sifting through silliness.

Machine Learning seems to have its basis in the pragmatic - a Practical observation or simulation of reality. Even within statistics, mindless "checking of models and assumptions" can lead to discarding methods that are useful.

For example, years ago, the very first commercially available (and working) Bankruptcy model implemented by the credit bureaus was created through a plain old linear regression model targeting a 0-1 outcome. Technically, that's a bad approach, but practically, it worked.

it's similar to using planet gravitational models to urban traffic. I find it absurd, but it works quiet accurately actually

I am interested in the last statement: "the very first commercially available (and working) Bankruptcy model implemented by the credit bureaus was created through a plain old linear regression model targeting a 0-1 outcome". Which model was it? I believe that the first model was RiskCalc by Moody's, and even the first version was a logistic regression model. The developers of that model were not CS people with a background in ML, but rather in econometrics.

I bet they used discriminant analysis before logistic regression, as DA was invented well before LR

@gappy I'm thinking of the MDS Consumer Bankruptcy model for individual credit bureau records.RiskCalc was a credit risk assessment for companies. The MDS Bankruptcy model differed from the FICO risk models of the time in that the target was Bankruptcy and NOT credit delinquency (such as FICO's original scores). My comment was less about the specifics of ML in that context (because it was barely in use -if at all- at the time the BK model was first built), but related to the fact that practical effectiveness is not necessarily at all related to theoretic restrictions or assumption violations.

Just curious why was it technically a bad approach though. Because it made too many simplifying assumptions that would vastly differ from the reality?

It was, in theory, a bad approach, because linear regression has baked-in assumptions about the underlying distributions of the data. In PRACTICE, the violations of those assumptions was irrelevant. The model worked, was robust and provided reliable & replicatable results.

I disagree with this question as it suggests that machine learning and statistics are different or conflicting sciences.... when the opposite is true!

machine learning makes extensive use of statistics... a quick survey of any Machine learning or data mining software package will reveal Clustering techniques such as k-means also found in statistics.... will also show dimension reduction techniques such as Principal components analysis also a statistical technique... even logistic regression yet another.

In my view the main difference is that traditionally statistics was used to proove a pre conceived theory and usually the analysis was design around that principal theory. Where with data mining or machine learning the opposite approach is usually the norm in that we have the outcome we just want to find a way to predict it rather than ask the question or form the theory is this the outcome!

I have spoken on this at a different forum the ASA Statistical Consulting eGroup. My response was more specifically to data mining but the two go hand in hand. We statisticians have snubbed our noses at data miners, computer scientists, and engineers. It is wrong. I think part of the reason it happens is because we see some people in those fields ignoring the stochastic nature of their problem. Some statisticians call data mining data snooping or data fishing. Some people do abuse and misuse the methods but statisticians have fallen behind in data mining and machine learning because we paint them with a broad brush. Some of the big statistical results have come from outside the field of statistics. Boosting is one important example. But statisticians like Brieman, Friedman, Hastie, Tibshirani, Efron, Gelman and others got it and their leadership has brought statisticians into the analysis of microarrays and other large scale inference problems. So while the cultures may never mesh there is now more cooperation and collabortion between the computer scientists, engineers and statisticians.

The real problem is that this question is misguided. It is not machine learning vs statistics, it is machine learning against real scientific advance. If a machine learning device gives the right predictions 90% of the time but I cannot understand "why", what is the contribution of machine learning to science at large? Imagine if machine learning techniques were used to predict the positions of planets: there would be a lot of smug people thinking that they can accurately predict a number of things with their SVMs, but what would they really know about the problem they have in their hands? Obviously, science does not really advance by numerical predictions, it advances by means of models (mental, mathematical) who let us see far beyond than just numbers.

+1 This reminds me of the use of models in economics. Econometric models are built for a couple of purposes; namely, policy analysis and forecasting. In general, nobody really cares about forecasting - it's the policy simulations that matter most. As David Hendry has been saying, the best forecasting model is not necessarily the best model for policy analysis - and vice versa. Need to step back and think... _What is the purpose of the model? What questions are we trying to answer?_ And how this fits in with _making empirical discoveries_.

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Shane 10 years ago

Thanks @robin; made CW. Although I don't entirely see this as "argumentative"; there are two fields which have informed each other (this is a fact), and the question is how much they have evolved together over the last decade.