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From |
Friedrich Huebler <huebler@rocketmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: Re: Weighted number of observations |

Date |
Tue, 3 Aug 2004 07:08:16 -0700 (PDT) |

Dear Toyoto, The auto data has 22 observations with foreign=1, not 50950. In [R] tabstat we read: "aweights and fweights are allowed; see [U] 14.1.6 weight." [U] 14.1.6 states that most Stata commands rescale the aweights to sum to N. However, -tabstat- does not rescale the weights. The fact that -tabstat- treats aweights the same way as fweights is not clearly documented. One could also argue that this behavior is inconsistent. Friedrich Huebler --- Toyoto Iwata <iwata@med.akita-u.ac.jp> wrote: > Dear Friedrich Huebler > > You wrote about > > > . tabstat foreign [aw=weight], stat(sum) > > > > variable | sum > > -------------+---------- > > foreign | 50950 > > ------------------------ > > Perhaps I miss the point, but, > > .gen eachmean = foreign*weight > > .gen sumeachmean = sum(eachmean) /* I don't know the mean of this. > */ > > . list sumeachmean in l > > +----------+ > | sumeac~n | > |----------| > 74. | 50950 | > +----------+ > > This seems to agree with the definition of the aweight. > > [Online help says,] > > aweights, or analytic weights, are weights that are inversely > proportional to the variance of an observation; i.e., > the variance of the j-th observation is assumed to be sigma^2/w_j, > where w_j are the weights. > Typically, the observations represent averages and the weights are > the number of elements that gave rise to the average. > > > > The Stata User's Guide states in section 14.1.6: "For most Stata > > commands, the recorded scale of aweights is irrelevant; Stata > > internally rescales them to sum to N, the number of observations > in > > your data, when it uses them." It would be useful if the Stata > > documentation could make clear which commands don't use aweights > in this manner. > > > > Friedrich Huebler > > sincerely, > > Toyoto __________________________________ Do you Yahoo!? Yahoo! Mail - 50x more storage than other providers! http://promotions.yahoo.com/new_mail * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: Re: Weighted number of observations***From:*Toyoto Iwata <iwata@med.akita-u.ac.jp>

**st: Suggestion for an added graph feature***From:*Fred Wolfe <fwolfe@arthritis-research.org>

**References**:**Re: st: Re: Weighted number of observations***From:*Toyoto Iwata <iwata@med.akita-u.ac.jp>

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