Group items tagged

The preceding scatterplot demonstrates that these data may not be linear.

In this tutorial, we will explore the a linear, quadratic, and cubic model.

To center a variable, simply subtract its mean from each data point and save the result into a new R variable, as demonstrated below.

Once the input variable has been centered, the higher order terms can be created.

we can simply multiply our centered term from step one and save the result into a new R variable, as demonstrated below.

Now we have all of the pieces necessary to assemble our linear and curvilinear models.

In this case, the quadratic and cubic terms are not statistically significant themselves nor are their models statistically significant beyond the linear model.

it can be helpful to summarize and compare our potential models using the summary(MODEL) and anova(MODEL1, MODEL2,… MODELi) functions.

The regression topics covered in these tutorials can be mixed and matched to create exceedingly complex models.

The good news is that more complex models can be created using the same techniques covered here. The basic principles remain the same.

R is an object oriented programming language. This means that virtually everything can be stored as an R object. Each object has a class. This class describes what the object contains and what each function does with it. For instance, plot(x) produces different outputs depending on whether x is a regression object or a vecto

The assignment symbol is "<-". Alternatively, the classical "=" symbol can be used.

Arguments are passed to functions inside round brackets (parentheses). One can easily combine functions. For instance you can directly type

The symbol "#" comments to the end of the line:

Commands are normally separated by a newline. If you want to put more than one statement on a line, you can use the ";" delimiter.

You can also have one statement on multiple lines. R is case sensitive: a and A are two different objects. Traditionally underscores "_" are not used in names. It is often better to use dots ".". One should avoid using an underscore as the first character of an object name.

Here are some things editors do to keep this book internally consistent. If you have something to contribute, go ahead and make your contribution. Other editors can touch up your edits afterwards so that they conform to the guidelines.

The local manual of style WB:LMOS for the R programming book, including a brief explanation of why we do it that way, is: Examples use "source" tags : <source lang="rsplus"> a <- 1:10 ; mean(a) </source>. That makes them look pretty to our readers. The name of packages are in bold  : '''Hmisc'''. Name of functions are in "code" tags: <code>lm()</code>. Page titles -- the part after "R Programming/" -- are in sentence case, like "R Programming/Working with data frames". We couldn't decide between sentence case and title case, so I flipped a coin. Every page has <noinclude>{{R Programming/Navigation}}</noinclude> at the top and {{R Programming/Navbar|Mathematics|Probability Distributions}} at the bottom. That makes it easier to navigate from one page to another online.