Statistics really is like rocket science it isn’t easy, even to us who have studied it for a long time. I’m not much of a stats person, but I tried – am I doing it right? Please compare this with: “I don’t know much about brain surgery, but my wife is suffering from and I plan to operate can you advise me?”įolks, just because you can plug numbers into a program doesn’t change the fact that if you don’t know what you’re doing, you’re almost guaranteed to get meaningless results – if not dangerously misleading ones. I’m especially proud of the dialog for retrospective power. If you follow those menu links, you get explanations of why not to do it. The other answer is that people ask me about this all the time, in spite of everything I say on this site. The technical answer to the question is that these menu items are inherited from a base class, along with some other things (e.g., the graphics capabilities). It seems to some to be placing undue emphasis on methods I don’t like. I have been asked why the Options menu in every single applet has links for retrospective power and Cohen effect sizes. I recommend against these (see Advice section below).
#POWER CALCULATION STATA HOW TO#
How to do… Retrospective power … Cohen’s effect sizes If you think your research is important, then it is also important to get good advice on the statistical design and analysis (do this before you start collecting data).
Most universities with statistics departments or statistics programs also offer a consulting service. If you need statistical advice on your research problem, you should contact a statistical consultant and if you want expert advice, you should expect to pay for it.
#POWER CALCULATION STATA SOFTWARE#
I need consulting help I am providing this software for free, but that does not obligate me to also answer substantive questions on power/sample size for your research project. Nothing has really changed here in a number of years, except for making the website more consistent with what’s happened to Java. Also, this is getting to be pretty old software. However, each applet has a help menu, and I do request that you carefully read that before you e-mail me with questions. I need help on using a particular applet I am willing to provide minimal support if you truly don’t understand what inputs are required. There are usually not nice neat formulas. Sample sizes are calculated using root-finding methods in conjunction with power calculations. In a few cases, an approximation is used, and is labeled as such. Typically it is a probability associated with a non-central distribution. What formula(s) do you use in these calculations? In most cases, power is an exact calculation based on the distributional situation in question.
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