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From |
Maarten buis <[email protected]> |

To |
[email protected] |

Subject |
Re: st: Re: Censored variables |

Date |
Thu, 17 Jan 2008 15:02:17 +0000 (GMT) |

So there are two types of processes: do I ever buy products x, y, and z, and if I buy products x, y, and z, have I run out of my private stock during the period under study. That should be moddelable, but maybe someone else on the list has more interesting comments to make... -- Maarten --- Andreas Drichoutis <[email protected]> wrote: > Dear Maarten. Thanks for your thorough response. > > The vector of censored binary variables X, contains variables that > indicate > if a person purchased a certain food product or not. Censoring occurs > at > zero because for some consumers we may not observe a purchase since > they may > have stockpiled food at home. We do not know the proportion of > censored > cases. We only suspect that some people may not have purchased a food > product because they stockpiled at home. > I need to create a variable that indicates the number of different > food > products purchased in the category i.e. a variety index which will be > the > sum of the X's. I'm not sure if the variety index should be > interpreted as a > count or a continuous variable. I then want to model variety as a > function > of several demographics and attitudinal variables. > Censoring is a major concern in my discipline. > > I hope I was more specific. So how do I go about it? > > P.S. The local specialist is not sure how to go about it, either > > Regards, > Andreas Drichoutis > > --- Andreas Drichoutis <[email protected]> wrote: > > Assume you have a vector of binary censored variables at zero, X, > and > > that you need to create a new variable that will be the sum of the > X's > > (e.g. V=X1+X2+.). What will be the problem if one uses V as a > > dependent variable in an OLS or count data model? How do you go > about > > it in Stata? > > Depends on the nature of the problem: > > o What do you mean with binary censored variable? > � - a binary variable that is sometimes censored, or > � - a continuous variable that is censored (and binary refers to your > ��� are either censored or not) > > o What is the process that leads to censoring? (is it censoring at > all) > � - Is it a variable cut off at 0, e.g. a propensity to give to a > ��� charity measured in euros could be negative (if one really > dislikes > ��� that charity) but is by law restricted to remain positive or > zero. > � - Is the censoring a two step process, e.g. one first decides > whether > ��� or not to given, and if one decides to give than one decides the > ��� amount. > � - are the variables counts (with or without an excessive amount of > ��� zeros) > > o How severe is the censoring? > � - What is the proportion of censored cases in each variable? > � - The sum of sencored variables is itself censored, but now the > ��� process is a bit more complicated (and thus more difficult to > ��� model). This censoring is more severe if the variables are > ��� strongly correlated, so if one is censored, the others are likely > ��� to be censored too. If you are interested in the sum of the > ��� variables, than they are probably strongly correlated, otherwise > ��� it would not make sense to combine them in a single variable. > > o What is the substantive interpretation of the sum of the censored > ��variables? > o What is the aim of your analysis? > o How puritan are you/the reviewers in you discipline/your advisor > with > � respect to these kinds or issues? > > On a more general note: these kinds of open question are much better > suited to a face to face discussion with a local specialist than a > discussion over e-mail. In my experience the most fruitfull way of > tackling such open questions is asking a lot of questions in return > (like the ones I have just asked), and in the process of answering > those question, you and the consultant can pin down the real problem. > All this presumes you have access to a local specialist... > > -- Maarten > > ----------------------------------------- > Maarten L. Buis > Department of Social Research Methodology > Vrije Universiteit Amsterdam > Boelelaan 1081 > 1081 HV Amsterdam > The Netherlands > > visiting address: > Buitenveldertselaan 3 (Metropolitan), room Z434 > > +31 20 5986715 > > http://home.fsw.vu.nl/m.buis/ > ----------------------------------------- > > > > * > * 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/ > ----------------------------------------- Maarten L. Buis Department of Social Research Methodology Vrije Universiteit Amsterdam Boelelaan 1081 1081 HV Amsterdam The Netherlands visiting address: Buitenveldertselaan 3 (Metropolitan), room Z434 +31 20 5986715 http://home.fsw.vu.nl/m.buis/ ----------------------------------------- __________________________________________________________ Sent from Yahoo! Mail - a smarter inbox http://uk.mail.yahoo.com * * 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/

**References**:**st: Re: Censored variables***From:*"Andreas Drichoutis" <[email protected]>

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