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From |
Steven Samuels <sjsamuels@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: New to Stata; wish to calculate sample size for kappa |

Date |
Mon, 2 May 2011 23:01:40 -0400 |

George- In addition, to -sskdlg- is the later -sskapp-, downloadable from SSC ("ssc download sskkapp") but it also applies to the binary outcome with two raters. I don't think that kappa exists for your situation All the examples that I've seen require multiple scenarios for the raters to assess. For a single video, you can only describe the proportions I mentioned and functions of those proportions; kappa doesn't appear to be such a function. Certainly statistics other than kappa that can measure agreement. A distribution in which one of the proportions is close to 1 and the others are small indicates excellent agreement. One measure which exploits this is: r = 1 - (entropy of observed distribution of p's)/(maximum possible entropy). where the denominator is the entropy corresponding to p1 = 1/3; p2 = 1/3; p3 = 1/3. See Wikipedia articles on "entropy". This measure doesn't take the ordinal nature of your scale into account. For example, it would have the same value for (1/2, 1/2, 0) and (1/2, 0, 1/2), when the former clearly shows better agreement. I have no experience or references in the use of entropy-based statistics for rater agreement, so you have some research to do. Good luck! Steve sjsamuels@gmail.com On May 2, 2011, at 8:59 PM, volsmd99 wrote: My goal is to calculate sample size for my scenario. I should mention that in addition to being new to stata, i am also new to kappa. For my case, I had the raters look at a video for which they could classify their opinion into three categories. Their choices were 0, 1, or 2. My Ko value is 0.80 (the level at which I considered Kappa to be significant) and my KL is 0.60 (minimum threshold value). Supposing a 95% confidence interval, I wish to calculate sample size. I have come across the package sskdlg but it seems to only allow sample size calculation with a binary outcome and with only two raters. thanks On May 2, 2011, at 3:12 PM, Steven Samuels wrote: > Welcome to Stata and Statalist! > > I don't really understand your question. If you have a number of raters and one subject, you can estimate the proportion of raters who assign each category to the subject. Call them p1, p2, p3, with p1 + p2 + p3 =1. How is kappa to be defined? > > Steve > sjsamuels@gmail.com > > > > On May 1, 2011, at 7:24 PM, volsmd99 wrote: > > Hi, > > I was previously a user of SAS and have recently switch to stata. > > My situation involves multiple raters on a 3 point ordinal scale. I have one subject. I am unsure which or if there is a package that will allow me to do this. > > thanks, George > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > > > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: New to Stata; wish to calculate sample size for kappa***From:*volsmd99 <volsmd99@gmail.com>

**Re: st: New to Stata; wish to calculate sample size for kappa***From:*Steven Samuels <sjsamuels@gmail.com>

**Re: st: New to Stata; wish to calculate sample size for kappa***From:*volsmd99 <volsmd99@gmail.com>

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