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Epidemiology and biostatistics, public health research. GLM, logistic regression, survival analysis, clinical trials.enSat, 20 Dec 2014 20:07:55 GMTvBulletin60http://www.talkstats.com/images/misc/rss.pngStatistics Help @ Talk Stats Forum - Biostatistics
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A dumb question about univariate analysis (repost from applied statistics)
http://www.talkstats.com/showthread.php/58935-A-dumb-question-about-univariate-analysis-(repost-from-applied-statistics)?goto=newpost
Fri, 19 Dec 2014 09:05:42 GMTHello
I'm quite dumb regarding statistics, but i really am looking for a simple answer to a simple question.
the question is: how do i explore data regarding a medium-sized (roughly 50-60) set of continuous variables measured in two group of samples (one "control" and one "test"?)

Let's imagine i have two wines which taste different, and i want to determine why they taste so different.

I take one glass of wine from each of three random bottles of each wine (let's assume the population of bottles of the same wine type is quite homogeneous, but not completely identical) and run each of the 6 taken samples (3 from the "control" wine and 3 from the "test" wine) through a GS-MS mass-spectrometers, and obtain roughly 60 peaks, each one corresponding to a compound present in the wine. Each peak's area is measured, giving a good quantitative measurement of how much of that compound is in each of the 6 samples. Now i have the quantities detected for each compound (obviously each compound measured is in a different scale, and possibly in a different unit, which means that one could be around 100 mg/L and the other could be in the vicinities of 3 mM).

Questions now:
- What statistical tests is suitable to understand if in the "test" wine the the measured compounds are present in different amounts as compared to the "control" wine? That is, how can we compare the means of the two groups for each of the variables tested?
- Is there a free program (preferably with a spreadsheet interface) that i can use to do the test?
- how can i explore the interrelation between variables? For example: is there a simple way(software) to check if increases in one compound are associated with decreases in another?

thank you very much and apologies in advance.
Andrea
]]>BiostatisticsKimbozhttp://www.talkstats.com/showthread.php/58935-A-dumb-question-about-univariate-analysis-(repost-from-applied-statistics)Two-proportion z test: is it best for my problem, and can I pool data?
http://www.talkstats.com/showthread.php/58930-Two-proportion-z-test-is-it-best-for-my-problem-and-can-I-pool-data?goto=newpost
Thu, 18 Dec 2014 21:24:08 GMTI am examining populations (cultures) of yeast cells and scoring them for a particular trait. The data is categorical; within a population, a yeast...I am examining populations (cultures) of yeast cells and scoring them for a particular trait. The data is categorical; within a population, a yeast cell either has the trait or it does not. I wish to compare two populations -- two genetically different strains of yeast -- to see whether there are differences in the proportion of of cells with the trait.

First question: would a two-proportion z test be the way to go here?

Second question: If so, in all of the examples I’ve seen the samples are taken from one “replicate” of each population. Working with yeast, I can set up multiple independent populations (cultures) for each particular strain (in my experiment I sampled four independent cultures for each of the two strains I examined -- scoring several million cells in each sample). Obviously in humans or many other populations such “replicates” are not possible. But for me they are. So my question is this: do you think it is valid to pool the data from all four replicates of each population? Or would it be best to show the calculation from one “representative” population for each?

I am not a statistician nor do I have good tools beyond Excel to do these calculations, so I am looking for a robust yet manageable approach to analyze my data. I can handle a Z test if that is the way to go, but if it's not a valid approach I would love to hear alternatives!

Thank you in advance!
]]>Biostatisticsdmcameronhttp://www.talkstats.com/showthread.php/58930-Two-proportion-z-test-is-it-best-for-my-problem-and-can-I-pool-data