Re: [R] odds ratio per standard deviation
Thanks, David, I appreciate your help. -- View this message in context: http://r.789695.n4.nabble.com/odds-ratio-per-standard-deviation-tp4669315p4669501.html Sent from the R help mailing list archive at Nabble.com. __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] odds ratio per standard deviation
On Jun 12, 2013, at 4:58 PM, vinhnguyen04x wrote: > L. Snow, > Ted, > > Many thanks, I am sorry to made a question without context. I use three > parameters of facial temperature, heart rate, and respiratory rate to > distinguish infectious patients from healthy subjects. So I use logistic > regression to generate a classification model and calculate the odds ratio > for these three parameters. In my case, I would like to know what kinds of > odds ratio can be used, odds ratio per standard deviation or odds ratio. > > Thanks you in advance for your help > The answer will depend on the distribution of the covariates, about which you have offered no information. It may also depend on what would be considered a relevant distance along the covariate "axes" by your audience. Generally odds ratios comparing a single year of increased age are not very interesting, but a difference of a decade will be understood by most audiences. Frank Harrell's rms/Hmisc package displays differences comparing the interquartile range. For heart rate I would think comparing a value of 80 to a value of 81 would nnot be thought of as clinically relevant. Most people are not capable of transforming odds ratios presented for a single unit difference to ones comparing a ten unit contrast. Differences of a degree of facial temperature might be more sensible given the narrow range over which temeperatures are maintained. It is your responsibility to make these decisions based on domain knowledge. Any knowledgeable practitioner of statistics can make transf! ormation to another contrast if enough digits of accuracy are offered. (It is rather frustrating to see published comparisons for single units of difference presented with minimal accuracy.) -- David Winsemius Alameda, CA, USA __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] odds ratio per standard deviation
L. Snow, Ted, Many thanks, I am sorry to made a question without context. I use three parameters of facial temperature, heart rate, and respiratory rate to distinguish infectious patients from healthy subjects. So I use logistic regression to generate a classification model and calculate the odds ratio for these three parameters. In my case, I would like to know what kinds of odds ratio can be used, odds ratio per standard deviation or odds ratio. Thanks you in advance for your help -- View this message in context: http://r.789695.n4.nabble.com/odds-ratio-per-standard-deviation-tp4669315p4669411.html Sent from the R help mailing list archive at Nabble.com. __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] odds ratio per standard deviation
[Replies transposed so as to achieve bottom-posting ... ] On 12-Jun-2013 14:53:02 Greg Snow wrote: > > On Tue, Jun 11, 2013 at 7:38 PM, vinhnguyen04x wrote: > >> Hi all >> i have a question: >> >> why and when do we use odds ratio per standard deviation instead of odds >> ratio? >> -- >> View this message in context: >> http://r.789695.n4.nabble.com/odds-ratio-per-standard-deviation-tp4669315.htm >> l >> Sent from the R help mailing list archive at Nabble.com. >> __ > > Without context this is a shot in the dark, but my guess is this is > referring to something like a logistic regression where the odds ratio > (exponential of the coefficient) refers to the change in odds for the > outcome for a 1 unit change in x. Now often a 1 unit change in x is very > meaningful, but other times it is not that meaningful, e.g. if x is > measuring the size of diamonds in carats and the data does not span an > entire carat, or x is measured in days and our x variable spans years. In > these cases it can make more sense to talk about the change in the odds > relative to a different step size than just a 1 unit change in x, a > reasonable thing to use is the change in odds for a one standard deviation > change in x (much smaller than 1 for the diamonds, much larger for the > days), this may be the odds ratio per standard deviation that you mention. > -- > Gregory (Greg) L. Snow Ph.D. > 538...@gmail.com I think there is one comment that needs to be made about this! The odds ratio "per unit change in x" means exactly what it says, and can be converted into the odds ratio per any other amount of change in x very easily. With x originally in (say) days, and with estimated logistic regression logodds = a + b*x, if you change your unit of x to, say weeks, so that x' = x/7, then this is equivalent to changing b to b' = 7*b. Now just take your sliderule; no need for R (oops, now off-topic ... ). Another comment: I do not favour blindly "standardising" a variable relative to its standard deviation in the data. The SD may be what it is for any number of reasons, ranging from x being randomly sampled fron a population to x being assigned specific values in a designed experiment. Since, for exactly the same meanings of the variables in the regression, the standard deviation may change from one set of data to another of exactly the same kind, the "odds per standard deviation" could vary from dataset to dataset of the same investigation, and even vary dramatically. That looks like a situation to avoid, unless it is very carefully discussed! The one argument that might give some sense to "odds ratio per standard deviation" could apply when x has been sampled from a population in which the variation of x can be approximately described by a Normal distribution. Then "odds ratio per standard deviation" refers to a change from, say, the mean/median of the population to the 84th percentile, or from the 31st percentile to the 69th percentile, or from the 69th percentile to the 93rd percentile, etc. But these steps cover somewhat different proportions of the populatipn: 50th to 85th = 35%; 31st to 69th = 38%; 69th to 93rd = 24%. So you are still facing issues of what you mean, or what you want to mean. Simpler to stick to the original "odds per unit of x" and then apply it to whatever multiple of the unit you happen to be interested in as a change (along with the reasons for that interest). Ted. - E-Mail: (Ted Harding) Date: 12-Jun-2013 Time: 17:14:00 This message was sent by XFMail __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] odds ratio per standard deviation
Without context this is a shot in the dark, but my guess is this is referring to something like a logistic regression where the odds ratio (exponential of the coefficient) refers to the change in odds for the outcome for a 1 unit change in x. Now often a 1 unit change in x is very meaningful, but other times it is not that meaningful, e.g. if x is measuring the size of diamonds in carats and the data does not span an entire carat, or x is measured in days and our x variable spans years. In these cases it can make more sense to talk about the change in the odds relative to a different step size than just a 1 unit change in x, a reasonable thing to use is the change in odds for a one standard deviation change in x (much smaller than 1 for the diamonds, much larger for the days), this may be the odds ratio per standard deviation that you mention. On Tue, Jun 11, 2013 at 7:38 PM, vinhnguyen04x wrote: > Hi all > > i have a question: > > why and when do we use odds ratio per standard deviation instead of odds > ratio? > > > > -- > View this message in context: > http://r.789695.n4.nabble.com/odds-ratio-per-standard-deviation-tp4669315.html > Sent from the R help mailing list archive at Nabble.com. > > __ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > -- Gregory (Greg) L. Snow Ph.D. 538...@gmail.com [[alternative HTML version deleted]] __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
[R] odds ratio per standard deviation
Hi all i have a question: why and when do we use odds ratio per standard deviation instead of odds ratio? -- View this message in context: http://r.789695.n4.nabble.com/odds-ratio-per-standard-deviation-tp4669315.html Sent from the R help mailing list archive at Nabble.com. __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
