search for: helsel

Displaying 10 results from an estimated 10 matches for "helsel".

Did you mean: selsel
2008 Sep 03
2
basic dataframe question
...ng: Why does my logical vector becomes a numeric vector when stuffed into a data frame? How do I change this so that it's retained as a logical data type? I've tried a couple of things but to no avail. Here's my example code: # Exercise 4-1 in Non-Detects and Data Analysis. Dennis Helsel. 2005. # "Create two new variables in the Interval Endpoints format, StartCu and EndCu, # that will contain the same information given by the current variables library(NADA) data(CuZn) names(CuZn) StartCu <- ifelse(CuZn$CuCen == "TRUE", 0, CuZn$Cu) EndCu <- CuZn$Cu CuIEP =...
2012 Aug 15
1
NADA package/cenboxplot() method: maximum censored percentage
...et of data has censored (less-than detection limits) water chemistry concentrations for 80-100% of all observations. My initial trial-and-error attempts to apply the cenboxplot() method suggests that it has an upper limit to the percentage of censored observations. I do not see this limit in Dennis Helsel's second edition. Has anyone experience plotting censored data and can provide me with the maximum percentage of censored data in a set of observations? TIA, Rich
2024 Jan 24
1
Use of geometric mean for geochemical concentrations [RESOLVED]
...ral Storm Water Discharge Permit for a point source such as a livestock feed lot you need only a single sample (after the rains start) to comply with the permit. Feh! Germane to Bert's comments about all the wrong ways to treat non-detected/censored water chemical analyses, I discovered Dennis Helsel by his 2005 article in Environmental Science & Technology (Oct. 16th). Bought his book when it was published in 2012 and have used survival analyses on censored data ever since. (Also presented a Continuing Legal Education talk in 2016 with a nice thank-you email from a state district judge who...
2012 Jun 05
0
NADA Applied to my Data
I need a nudge in the right direction to get started using NADA. I bought Helsel's second addition and am currently reading it; NADA is installed in R. My data has been restructured with a couple of awk scripts. The data frame structure now has a flag if the quantity is censored (ceneq1 column) as well as a lower and upper limit for censored data. For present purposes,...
2012 Jun 06
0
R-help Digest, Vol 112, Issue 6
...oject.org > Subject: [R] NADA Applied to my Data > Message-ID: > <alpine.LNX.2.00.1206050931300.27613@salmo.appl-ecosys.com> > Content-Type: TEXT/PLAIN; format=flowed; charset=US-ASCII > > I need a nudge in the right direction to get started using NADA. I bought > Helsel's second addition and am currently reading it; NADA is installed in > R. > > My data has been restructured with a couple of awk scripts. The data frame > structure now has a flag if the quantity is censored (ceneq1 column) as well > as a lower and upper limit for censored...
2005 Dec 17
2
diagnostic functions to assess fitted ols() model: Confidence is too narrow?!
Dear all, When fitting an "ols.model", the confidence interval at 95% doesn't cover the plotted data points because it is very narrow. Does this mean that the model is 'overfitted' or is there a specific amount of serial correlation in the residuals? Which R functions can be used to evaluate (diagnostics) major model assumptions (residuals, independence, variance) when
2008 May 12
4
Left censored responses in mixed effects models
Dear R Fellow-Travellers: What is your recommended way of dealing with a left-censored response (non-detects) in (linear Gaussian) mixed effects models? Specifics: Response is a numeric positive measurement (of volume, actually); but when it falls below some unknown and slightly random value (depending on how the sample is prepared and measured), it cannot be measured and is recorded as 0.
2024 Jan 22
3
Use of geometric mean for geochemical concentrations
A statistical question, not specific to R. I'm asking for a pointer for a source of definitive descriptions of what types of data are best summarized by the arithmetic, geometric, and harmonic means. As an aquatic ecologist I see regulators apply the geometric mean to geochemical concentrations rather than using the arithmetic mean. I want to know whether the geometric mean of a set of
2010 Jul 06
3
Help With ANOVA (corrected please ignore last email)
Sorry i had a misprint in the appendix code in the last email Hi I needed some help with ANOVA I have a problem with My ANOVA analysis. I have a dataset with a known ANOVA p-value, however I can not seem to re-create it in R. I have created a list (zzzanova) which contains 1)Intensity Values 2)Group Number (6 Different Groups) 3)Sample Number (54 different samples) this is created by the
2012 Aug 31
3
fitting lognormal censored data
Hi , I am trying to get some estimator based on lognormal distribution when we have left,interval, and right censored data. Since, there is now avalible pakage in R can help me in this, I had to write my own code using Newton Raphson method which requires first and second derivative of log likelihood but my problem after runing the code is the estimators were too high. with this email ,I provide