# Tagged Questions

LOESS (or LOWESS) stands for locally weighted scatterplot smoothing. It is a form of local (k-nearest neighbor) kernel regression

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### Finding inflection points in R from smoothed data

I have some data that I smooth using loess. I'd like to find the inflection points of the smoothed line. Is this possible? I'm sure someone has made a fancy method ...
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### interpretation from loess graph

I have measured events X and Y in two strains (A and B) of same species. After calculating the values of these X and Y, I compared them with wild type values (X and Y) to calculate fold change. I have ...
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### Combining many small regressions to answer question “what was most related?”

I have an interesting data set for which I want to answer the question: Question How do I rank consumption of a key resource from my data set. I am not interested in predicting, rather measuring ...
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### Smoothing algorithm for saturating function

I have a noisy readout of a curve that is monotonically increasing or decreasing for a narrow range of points and then quickly saturates. I don't know exactly where the saturation point is, but from ...
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### LOESS and MA normalization in R?

Attempting to do loess on two variables x and y in R using MA normalization (http://en.wikipedia.org/wiki/MA_plot) like this: ...
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### Repeated loess smoothing for time series data

I have 3 time series and I would like to determine if there are any common patterns in the data. Zuur mentioned in one of his books that a reasonably simple approach to test this is based on repeated ...
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### With a binary Y, why are R's lowess fits so often flat?

I'm trying to explore (rather than formally test) relationships for various subgroups between a continuous X and a binary Y (0 or 1). A good shortcut would seem to be to graph a smoothed X-Y fit for ...
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### local polynomial regression standard errors

I am attempting to find a reference which explains how one computes standard errors for local polynomial regression? Specifically, in R one can use the loess ...
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### How to compare loess models from related datasets?

I'm comparing matched data from a series of patients, looking at the effect of mental stress on cardiac conduction. I'm using the loess function to visually describe my data, and have 2 curves: one ...
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### What is the difference between simple linear model and loess model?

Can somebody explain to me the difference between linear model and loess model in statistics? I need to explain this to non-math people.
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### How to get an R-squared for a loess fit?

How to calculate R-squared ($r^2$) statistic in R for loess and/or predict function output? For example for this data: ...
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### Creating univariable smoothed scatterplot on logit scale using R

I am learning logistic regression modeling from the book Applied Logistic Regression by Hosmer. I need to create a plot named "create univariable smoothed scatterplot on logit scale", something like ...
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### Comparing smoothing splines vs loess for smoothing?

I wish to better understand the pros/cons for using either loess or a smoothing splines for smoothing some curve. Another variation of my question is if there is a way to construct a smoothing spline ...
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### Effective cutoff frequency for LOESS smoothing

I need to vary the window width (span) of a LOESS smoothing filter to select a given effective lowpass filter frequency. When I was using Savitzky-Golay for smoothing I found this technical report ...
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### How to plot multiple loess curves in a xyplot panel data?

Imagine the following simplified longitudinal data with 4 individuals and 3 variables (y1, y2, y3) measured at 50 occasions : ...
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### Is there a “pure R” implementation for loess? (with no C code?)

I would like to manipulate the work done by the loess function in R. However, the main workhorse of this function is written in C. Is there some pure R implementation of the code? Thanks.
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### How to choose a span parameter with LOESS?

What common methods are used for choosing the smoothing parameter for LOESS? (In R, but also in general).
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### What is nonparametric logistic regression based on locally weighted scatterplot smoothing?

Recently, I read an article regarding the association between age and lymph node metastases. The authors stated that: "Because a nonlinear relationship between age and lymph node involvement ...
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### Trend or no trend?

I have a quarterly time series and test for stationarity with an augmented Dickey-Fuller test using R. ...