Continue to discuss this topic about multicollinearity in regression. Firstly, it is necessary introduce how to calculate the VIF and condition number via software such as R. Of course it is really easy for us. The vif() in car and kappa() can be applied to calculate the VIF and condition ... [Read more...]

As we all know, there are a lot of packages provide functions to plot maps, such as ggmap, GEOmap, rworldmap and so on. For visualizing 2D topographic map, here is a good example. Besides, 3D topographic map is also easily to be plotted via some excellent functions and packages. The ... [Read more...]

In multiple regression analysis, multicollinearity is a common phenomenon, in which two or more predictor variables are highly correlated. If there is an exact linear relationship (perfect multicollinearity) among the independent variables, the rank of X is less than k+1(assume the number of predictor variables is k), and the ... [Read more...]

The day before yesterday is spring festival which is one of the most famous Chinese festivals, and setting off firecrackers outside on New Year Eve is a traditional custom. However, firecrackers will pollute circumstance severely and cause the hazy weather. Of course the pollution of different province is not the ... [Read more...]

These days I became interested in financial data, such as stock price, exchange rate and so on. Obviously there are a lot of available models to fit, analyze and predict these types of data. For instance, basic time series model arima(p,d,q), Garch model, and multivariate time series ... [Read more...]

Cluster analysis is widely applied in data analysis. Obviously hierarchical clustering is the simple and important method to do clustering. In brief, hierarchical clustering methods use the elements of a proximity matrix to generate a tree diagram or dendogram. From the tree diagram, we can draw our own conclusions about ... [Read more...]

Although 2013 was not perfect for me, it still gave me a lot of happiness and beneficial experiences which were worthy to recall.  It is in 2014 that numerous difficult problems need to be solved. Application is still a headache and the final tests are also troublesome. Whereas,  2014 is full of hope. ... [Read more...]

In general, TOEFL(Test of English as a Foreign Language) is not an easy test for Chinese students, including me.  Relatively speaking, the reading section is little easier than the other sections (listening, speaking, writing). Interestingly, when I prepared my TOEFL test, I found that some important words appeared frequently ... [Read more...]

Principal component analysis(PCA) is one of the classical methods in multivariate statistics. In addition, it is now widely used as a way to implement data-processing and dimension-reduction. Besides statistics, there are numerous applications about PCA in engineering, biology, and so on. There are two main optimal properties of PCA,  ... [Read more...]