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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
RE: st: Time series - what to do before a product launch?; how to count n obs showing an attribute in each year? |

Date |
Mon, 12 Apr 2010 18:57:15 +0100 |

The larger question here is "How should I model this?" which is difficult at the best of times and in any case better left to subject-matter experts. The smaller question is more my thing. egen sum = total(generic == 1), by(subclass quarter) may be the sort of solution you need. Nick n.j.cox@durham.ac.uk Rodrigo Refoios Camejo [edited] I have 10 years of panel data on pricing and quantities sold of pharmaceuticals. For each presentation (i.e. dosage and package) of each product I have data on the prices and quantities sold in each quarter. My idea is to fit a regression model with price as the dependent variable and independent variables related to competition like: # products in the therapeutic class at time of launch; # generics in the therapeutic class at time t; market share of market leader at time t; price of market leader at time t-1; etc. How can I deal with the fact that some products were only launched half-way the data timeframe and some were discontinued after launch, i.e. when price=="0" & quantity=="0" for all t before t launch and for some after t launch. How can I have Stata including in the regression only the data for which price and quantity is available? Simply drop if price==0? Will it not treat it as missing if I do so? Another side question, how can I make Stata count the # products with a particular characteristic (e.g. generic==1) marketed in each group (subclass) of drugs in each quarter? And then assign to each product the count corresponding to the quarter in which that product was launched? * * 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/

**Follow-Ups**:**Re: st: Time series - what to do before a product launch?; how to count n obs showing an attribute in each year?***From:*Rodrigo Refoios Camejo <refoioscamejo@gmail.com>

**References**:**Re: st: Time series - what to do before a product launch?; how to count n obs showing an attribute in each year?***From:*Rodrigo Refoios Camejo <refoioscamejo@gmail.com>

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