This is an situation that causes researchers to react in different ways. Some grapple with it, others exploit it, many avoid it. If you have experience with controversial research, your comments will be summarized and posted so others can benefit.
Niche products, niche businesses, niche markets -- small businesses are often qualified as surviving in niches, finding their niche, defining or redefining their niche. Most people think entrepreneurs start their own business, but most buy running ventures, like franchises, already in surviving niches. Steps to understanding and predicting quantitative business niches are in early stages.
Here are some sources of numeric information that could be used. Web listing of businesses for sale on the Read more [...] one
Demetris Koutsoyiannis responds:
I agree that a bimodal distribution is seldom seen. Well, my experience is not from ecological but mainly from hydrological processes but I suspect that the behaviours would be similar.
I have seen claims of bimodality several times but I was never convinced about them as I did not read any argument supporting it except empirical histograms. However, we must be aware that the uncertainty of the histogram peaks is large. A simple Monte Carlo experiment with say a Read more [...] 14 com
The third ecological question for today ventures into the field of evolutionary biology. Any answers will be posted.
Here is the first of a series of ecological modeling questions? Post an answer in the comments and I will transfer it up to the post body.
Before I attempt to describe my answer, I would like to do some clarifications on the nature of a statistical prediction and mention some points than need caution.
1. A statistical prediction should be distinguished from a deterministic prediction. In a deterministic prediction some deterministic dynamics of the form y = f(x1, â€¦, xk) are assumed, where y is the predicted value, the output of the deterministic model f( ), and x1, â€¦, xk are inputs, i.e. explanatory Read more [...] none
Thanks to Martin Ringo for this answer.
Let me offer a little of the terminology of forecasting, which, I hope, will make the question clearer. When you are forecasting from some kind of structural model, say Y = f(X1, â€¦, Xk), there is a difference in whether you have to forecast the Xs as well as the Y. If you donâ€™t, it is an unconditional forecast; if you do, it is conditional. For an unconditional forecast, the inference is a pretty straightforward exercise of the classical linear Read more [...] none
The question for today. Does anybody know of any unprecedented warmth down under?
Demetris Koutsoyiannis responds:
I think that such questions should not be treated in an algorithmic manner and that it is important to formulate them in the clearest and most consistent manner.
So, let us assume that we have a nonstationary stochastic process X(t) and a stationary process Y(t); I have interpreted here â€œvariableâ€ as process because the notion of stationarity/nonstationarity is related to a (stochastic) process, not a variable. Is the question, how to establish a regression Read more [...] 4 com
Martin Ringo responds:
This is the wrong question. The analyst shouldnâ€™t be worried about whether the dependent or independent is stationary or non-stationary. The issue is the error term.
In the Box-Jenkins procedure(s) â€” or maybe I should call it paradigm â€” the non-stationary stuff is removed. To me that removal is what is interesting, and all the stuff that Messrs. Box and Jenkins do is the treatment of serial correlation. But be you structural econometrician or time-series Read more [...] 5 com
Thanks for the answer to this question by Demetris Koutsoyiannis
I think that statistical predictions tend always to the mean as time increases. If we use the maximum entropy principle to obtain these predictions, the result depends on the time scale of entropy maximization. For instance, if the entropy maximization is done on the observation time scale, then the prediction may be equivalent to a prediction obtained by a Markov model. However, other settings of entropy maximization (on several time Read more [...] one
One of the main inputs into a niche model is the environmental variables. Optimizing the choice of variables is important for many reasons, primarily interpretation and subsequent accuracy on independent test data.
In almost all cases to date, annual climate averages have been used in modeling species distributions. Where models have been developed and annual averages of climate compared with monthly variables and others such as vegetation, improvements in the accuracy were attributed to the monthly Read more [...] 4 com
The post Bayesian Networks introduced this useful and flexible form of modeling. Here is an example of a Bayesian Belief Net or BBN model of a simple three variable species prediction system.
In Fig 1 the top node is habitat quality for the species. Two lower nodes, the average temperature (Av_Temp) and the vegetation (Veg_Type) at the site, represent simple environmental variables, related to presence of the species. In Av_Temp, the probability of the species being present is a bell shaped curve Read more [...] none
The previous post "Writing a Book Using R" described using latex for writing a book, saving time with one master bibliography and other organizational devices. Sweave allows R code to be included in a latex file. This is a good marriage; while latex provides typeset text; R is statistically and graphic oriented.
Here is an example of the overall steps one would take to compile a combined latex and R code document for publication.
Part of the latex is generated by the Sweave package in R, not Read more [...] none
Long-range dependence is being identified many disciplines such as, networking, databases, economics, climate and biodiversity. LTP is competing with the sexy "long tail" for top spot as a theory of cultural consumption. Thus, the need for software offering complete long-range dependence analysis is crucial.
While there are some steps towards this direction, none are yet completely satisfactory. For one, the Hurst exponent cannot be calculated in a definitive way, it can only be estimated. Second, Read more [...] 3 com
A number of posts here and here have compared the "hockey stick" construction of past temperatures to the play by Rolin Jones to illustrate an area of science where dramatization and self-promotion have become confused with the search for scientific truth. The background of this story is fascinating.
In a story on the playwright at theatermainia.com relates the story behind the play.
In doing research for the play, Jones was lucky to have as a resource the library at Yale University, where he Read more [...] none
One of the best, and possibly the only, guide to advanced use of R is the manual "Econometrics in R" by Grant V. Farnsworth. Dated June 26, 2006 it was originally written as part of a teaching assistantship and personal reference. Some of the topics covered I have found nowhere else. The manual is particularly through in treatment of regression, i.e.:
3 Cross Sectional Regression
3.1 Ordinary Least Squares
3.2 Extracting Statistics from the Regression
3.3 Heteroskedasticity and Friends
3.3.1 Read more [...] none
We use the data from CRU, and input it into R using the code in the post R Code to Read CRU Data. The initial approach to testing whether global temperatures from CRU is to run a Dickey-Fuller Test for Unit Root.
The augmented Dickey-Fuller test checks whether a series has a unit root. The default null hypothesis is that the series does have a unit root.
A unit root refers to the coefficeint b in the sequence being greater than one and leads to series with a tendency to wander infinitely far from Read more [...] none
According to Wikipedia the mathematical model for Brownian motion (also known as random walks) can also be used to describe many phenomena as well as the random movements of minute particles, such as stock market fluctuations and the evolution of physical characteristics in the fossil record. The simple form of the mathematical model for Brownian motion has the form:
St = eSt-1
where e is drawn from a probability distribution. My initial implementation of Brownian motion in R and 2 dimensions Read more [...] 13 com
Reading CRU data is an opportunity to demonstrate some of the features available for programming in R. The Climate Research Unit (CRU) data is a record of the global, northern and southern hemisphere temperatures compiled from temperature sources around the globe for the last 150 years. The files are located at http://www.cru.uea.ac.uk:80/cru/data/temperature/ and look like this, with alternating lines of numbers and values for each month, and annual averages at the end:
1856 -0.405 -0.486 -0.985 Read more [...] none
The Washington Post has finally commented on the Wegman Report, and Whitfield hearings I and II on the so-called "hockey stick" graph -- a trend line that purports to show little temperature variation throughout the Medieval Warm Period and a sudden and dramatic increase in global temperatures in the 1990s and therefore looks like a hockey stick. Their position:
The graph is hardly central to the modern debate over climate change. Yet the subcommittee has investigated the scientists who dared produce Read more [...] none
A "simple" regression model is simple because it has a single independent variable instead of multiple independent variables. Because simple is in the name, many people make the mistake of thinking they are simple to use. One mistake is to first apply them to their data, without checking to see if the assumptions are met. Here is a useful web page from Duke University called Not-so-simple Regression Models describing a general approach to developing simple linear regression models.
They provide Read more [...] one
Emotional Intelligence or EI is a concept popularized by Daniel Goleman
as a complement to competence measures like IQ in the emotional
sphere. But EI has the problem that it is not quantitatively defined
with a number and standards like IQ. So it has been criticized by
people like Eysenck:
"exemplifies more clearly than most the fundamental absurdity of the tendency to class almost any type of behavior as an 'intelligence'."
Statistics are the quintessential antiemotional tollgate.
The "Little Read more [...] none
The previous post "Random Numbers Predict Future Temperatures" used random numbers for prediction of climate. Random numbers may also be predicted. This is a major difference between models and natural phenomena. Random numbers generated by computer can always be predicted exactly given knowledge of the code, and so have a deterministic generating mechanism, or model.
The above series of numbers appears to be a temperature trend such as 20th century warming, composed of random fluctuations Read more [...] 3 com
If a picture is worth a thousand words, a video is worth more. The use of compelling media has been undergoing something of a revolution recently, driven by new social sites like YouTube. I like Salsa music, and found this clip of the Colombian band Guayacan (I think I saw these guys in Mexico City in 1997 - amazing act). If thatâ€™s a little too strong for your taste, here is another Colombian Salsa band
Grupo Niche. The YouTube science category has some cool robot clips.
One Read more [...] none