Hi, I am currently doing my third year dissertation project and need some advice. Before I ask any questions, it may be best to give some information about my study. * Its a 2x2x2 independent…Continue
Started by Phil Davies. Last reply by Phil Davies on Sunday.
I am teaching statistics to students in psychology. My university used statistica and I want to change for R. Thus, I opened the book of Andy Field and followed all the instructions. No problem was…Continue
Started by Nicolas Stefaniak. Last reply by Nicolas Stefaniak Mar 14.
Hello,I am new to this group and I have questions both general and specific about linear models.I’ve read the book "Discovering statistics using IBM SPSS statistics" 4th Edition, mostly.General…Continue
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I am working on a study that includes a large number of groups, different doses and control groups. This study involved administering two drugs. The first drug was given as a pretreatment to block…Continue
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Hi all,
I'm very pleased to let you know that SAGE has recently set up a new Facebook page about all things Andy and Discovering Statistics, where we'll be posting news, free stuff, photos, videos, competitions and more. We've just posted the second video in our Ask Andy Anything series which is well worth a watch! Hope you can join us over there:
I'm sorry that I posted a new discussion item as a comment to this thread. I now understand where it should have gone.
Hi,
I am new to R and am learning using DSUR. On page 78 it is suggested that we load a package called DSUR in order to have handy the functions in the book. The current DSUR package is not compatible with R v 2.15.2. Do we simply cut and paste from the book's website? Is there a new DSUR package out there that I have missed?
All the best,
C Moller
Thanks Katie. Have sent to the group hoepefully with luck i will get some hints.
Hi everyone,
I am doing ROC Curve analysis to establish cut-off points for a scale. I calculated Youden's index to establish cut-off points, however to my despair, the Youden's index is equal for two of the scores:
Let's say my subjects could score between 10-20 on a scale and the Youden's index is the highest at 124.5 for scores 15 and 16 on this scale. I wonder what would be the best cut-off: 15 and 16?!
obviously sensitivity is higher on one score and the specificity for the other
Thank you for your help
Dear Andy and All
I have a question about data transformations. Consider the following explanation written by Andy:
“As such, transforming the data won’t change the relationships between variables (the relative differences between people for a given variable stay the same), however, it does change the differences between different variables (because it changes the units of measurement). Therefore, even if you have only one variable that has a skewed distribution, you should still transform any other variable sin your data set if you’re going to compare differences between that variable and others that you intend to transform.”
My concern is the following: I understand Andy's argument about changing the units of measurement, but what will happen if you transform a variable that is normal? Will it become skewed? If so, what is the use then of transforming the skewed variable(s)? Maybe I am missing something. Looking forward to some advice.
Best wishes
Henry
Mutasem,
There's a decent description of post hoc tests here: http://pages.uoregon.edu/stevensj/posthoc.pdf
In short, different post hoc tests scale the F-ratio differently. Depending on how the F-ratio is distributed, you may end up with n.s. contrasts (common in Scheffe's method).
Hello
I wonder how is it possible to get a significant omnibus F in one-way ANOVA, and getting no significant differences in a post hoc test ?
yey I am part of this group...
Thank you so Much Oscar, will try it.
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