search for: geochemical

...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 chemical concentrations (e.g., > in mg/L) is an appropriate representation of the expected value. If not, I > want to explain this to non-technical decision-makers; if so, I want t...

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 chemical concentrations (e.g., in mg/L) is an appropriate representation of the expected value. If not, I want to explain this to non-technical decision-makers; if so, I want to understand wh...

Dear Rich, It depends how the data is generated. Although I am not an expert in ecology, I can explain it based on a biomedical example. Certain variables are generated geometrically (exponentially), e.g. MIC or Titer. MIC = Minimum Inhibitory Concentration for bacterial resistance Titer = dilution which still has an effect, e.g. serially diluting blood samples; Obviously, diluting the

On Mon, 22 Jan 2024, Bert Gunter wrote: > better posted on r-sig-ecology? -- or maybe even stack exchange? Bert, Okay. Regards, Rich

I think https://stats.stackexchange.com would be best: r-sig-ecology is pretty quiet these days On 2024-01-22 11:05 a.m., Rich Shepard wrote: > On Mon, 22 Jan 2024, Bert Gunter wrote: > >> better posted on r-sig-ecology? -- or maybe even stack exchange? > > Bert, > > Okay. > > Regards, > > Rich > > ______________________________________________

On Mon, 22 Jan 2024, Rich Shepard wrote: > 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 chemical concentrations (e.g., > in mg/L) is an appropriate representation of the expected value. If not, I > want to explain this to non-technical decision-makers; if so, I want t...

Hello all, I'm dealing with geochemical analyses of some rocks. If I use the full composition (31 elements or variables), I can get reasonable separation of my 6 sources. Then when I go onto do LDA with the 6 groups, I get excellent separation. I feel like I should be reducing the variables to thos that are providing the most discrimi...

Hi, I am trying to create what are called "spider diagrams" in the geochemical literature using R. A spider diagram is basically a plot of the atomic number versus the concentration on a log scale. Lines are drawn from each atomic number for each sample. Right now, my data frame looks like: SAMPLE SITE V3 LA.NASC LAATNUM CE.NASC CEATMNUM 1...

...he Geochem Data") bstick.env<- bstick(19, tot.var=19) #must change number based on number in bstick model bstick.env geopca plot(bstick.env, type="o", lty="dotted", ylim=range(bstick.env, geopca$CA$eig), xlab="PCA Axis", ylab="Inertia", main="Geochemical ITRAX Data: Bstick") points(geopca$CA$eig, type="o", col="red") plot(geopca, scaling=2) env.sc<- scores(geopca)$species plot(geopca, scaling=2) arrows(0, 0, env.sc[,1]*0.85, env.sc[,2]*0.85, col="red", length=0.05) Does anyone know a more suitable code? I...

...the best "a priori" transformation for such data -- with the one advantage even that you need to fiddle with zeroes when log-transforming, whereas the geometric mean works already for zeroes. Martin > 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 chemical concentrations (e.g., > in mg/L) is an appropriate representation of the expected > value. If not, I want to explain this to non-technical > de...

...in > health distress: apply First Aid -- do the things you learned to do > quickly without too much thought, because things must happen fast ---to > hopefully save the other's life. Martin, Thanks very much. I will look further into this because toxic metals and organic compounds in geochemical collections almost always have censored lab results (below method dection limits) that range from about 15% to 80% or more, and there almost always are very high extreme values. I'll learn to understand what benefits log transforms have over compositional data analyses. Best regards, Rich

...irst Aid -- do the things you learned to do > > quickly without too much thought, because things must happen fast ---to > > hopefully save the other's life. > > Martin, > > Thanks very much. I will look further into this because toxic metals and > organic compounds in geochemical collections almost always have censored > lab > results (below method dection limits) that range from about 15% to 80% or > more, and there almost always are very high extreme values. > > I'll learn to understand what benefits log transforms have over > compositional data anal...

...of proteins is based on a published group additivity algorithm and is further supported in this package by the inclusion of data files for the amino acid compositions of selected proteins and of proteins in yeast and E. coli. A paper describing some applications of the package can be found in Geochemical Transactions: http://www.geochemicaltransactions.com/content/9/1/10 The project website highlights many of the example calculations. There is also an Rpad script available for download that presents basic functionality of the program in a browser interface. The website is located at: http://w...

Not so much an R question, as a methodology one... Dealing with some reviewers comments, one of the reviewers suggests bootstrapping my group means and standard deviations since 2 of my 3 groups have a small sample size. My data is geochemical data, and a variety of clustering methods finds 3 groups in the data. One group has 50 members, another group has 10 members and another group 12 members. LDA with cross-validation gives a 92% correct classification rate. Anyway, my question is this--- WHat is the best or proper way to present...

...of proteins is based on a published group additivity algorithm and is further supported in this package by the inclusion of data files for the amino acid compositions of selected proteins and of proteins in yeast and E. coli. A paper describing some applications of the package can be found in Geochemical Transactions: http://www.geochemicaltransactions.com/content/9/1/10 The project website highlights many of the example calculations. There is also an Rpad script available for download that presents basic functionality of the program in a browser interface. The website is located at: http://w...

...u learned to do >> > quickly without too much thought, because things must happen fast ---to >> > hopefully save the other's life. >> >> Martin, >> >> Thanks very much. I will look further into this because toxic metals and >> organic compounds in geochemical collections almost always have censored >> lab >> results (below method dection limits) that range from about 15% to 80% or >> more, and there almost always are very high extreme values. >> >> I'll learn to understand what benefits log transforms have over >>...

Dear Sir I would appreciate recieving the manul instruction of the program foe geochemical calculations.please what are the requirmentsof using the program Thanks Tanat university faculty of science , geology department ,tanta Egypt Prof.Mohamed Fouad Ghoneim Ph.D- D.Sc. Head of Geology Department Faculty of Science Tanta University, Egypt www.profghoneim.tk ---------------------...

...ype: TEXT/PLAIN; charset=US-ASCII There are some pointers to packages for variable selection in the task view for Chemometrics and Computational Physics at http://cran.r-project.org/web/views/ChemPhys.html On Sun, 21 Sep 2008, Gareth Campbell wrote: > Hello all, > > I'm dealing with geochemical analyses of some rocks. > > If I use the full composition (31 elements or variables), I can get > reasonable separation of my 6 sources. Then when I go onto do LDA with the > 6 groups, I get excellent separation. > > I feel like I should be reducing the variables to thos that are...