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Description:
A discussion group for anyone with an interest in Medical Statistics.
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Population Attributable Risk (PAR) from Cross Sectional Studies?
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Hello Forumers:
I have a question. I am trying to wrap my head around the calculation
and use of Population Attributable Risk based on a cross sectional
study.
From my basic epidemiology courses, I have come to understand that
such an estimate is only reasonable when one can make plausible
assumptions of causality. Given that cross sectional studies are... more »
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{MEDSTATS} Trajectory modelling, useful with only two timepoints?
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Thomas Fröjd <tfr...@gmail.com> wrote ...I've never used PROC TRAJ (never even heard of it) but I'd hesitate to call something with only two timepoints a trajectory. Patterns in recovery are too complex to be captured with only two time points. I am also leery of classifying number of symptoms into "low" and "high" unless there is a clear separation.... more »
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Trajectory modelling, useful with only two timepoints?
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Hi.
I am working with a researcher analysing data following a number of
individuals on two timepoints. The measurements we are interested in
are the number of PTSD symptoms they have on each timepoint.
The researcher I work with suspect that there are a number of
naturally occuring subpopulations among the individuals with diffrent... more »
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confidence interval calculation
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Dear all, I am looking for help to calculate the confidence interval around Observed - Expected. My expected values come from a logistic regression model. Any suggestions would be most appreciated.
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{MEDSTATS} ANCOVA
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Jeff <ebsp...@gmail.com> wrote ...More confusion caused by the diverse origins of statistics. ANCOVA, ANOVA, OLS regression are all the same model in matrix terms Y = XB + e the various X can be interval, or categorical or dichotomous, or whatever. The ANOVA/ANCOVA stuff comes from agriculture, where they compared plots of land.... more »
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ANCOVA
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Greetings all,
I have a question about ANCOVA which I've wondered about for some
time. I've seen several sources (textbooks) which explicitly state
that covariates used in this analysis must be of continuous scale.
However, I've also seen a number of studies which have used gender as
a covariate. My understanding is that ANCOVA uses linear regression... more »
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{MEDSTATS} Ratios as DVs and IVs: BMI (was Re: Interestingresults, how to deal with these interaction effects?)
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John Sorkin <jsor...@grecc.umaryland.edu> wrote ...I would not divide BMI (or any measure) into "working" and "not working", rather, I'd say it's completely nonsensical for some people (e.g. athletes) and only partly nonsensical for others. For the very obese, it may be the best available measure. And I wouldn't say BMI has NO uses; but it is abused drastically. It is abused by insurance companies, who use it to raise premiums or deny coverage to people based on BMI. It is abused by people who take their own BMI and then conclude (perhaps erroneously) that they are fat or not fat. It is also abused by being categorized into (usually) four categories - categorization of a variable like this makes little or no sense. Of course, the categorization is not a problem specific to BMI, but it's done very often with BMI. If a person gains 2 pounds, he shifts from "normal" to "obese" - I think we can all agree this is silly.... more »
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A version of the Nigerian Hoax?
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Dear medstatters.
I recieved an email from a student in India who wanted to retain my
services as a statistical consultant to his thesis (I live in Israel).
He claims he got my info from Yahoo groups.
He expressed willingness to wire me cash in advance, prior to any
serious input from me.
This looks like an intelligent version of the infamous Nigerian Hoax.... more »
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For stats geeks - article has me confused I think they messed up
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Good afternoon A client asked me to replicate some analyses done in another paper with new data. But I think the paper messed up the analysis. I don't want to post the details to the whole list, but if someone wants to take a look and tell me if I am confused or the authors are, contact me off list.... more »
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confidence interval around a total
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Dear all, A colleague of mine wants to estimate the total number of people in the population with a certain characteristic (X). He has run a survey and from this has calculated the probability of X by another variable (say household type, 10 categories, hence 10 values of X), he now wants to apply these... more »
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