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

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

Subject |
st: RE: how to generate groups based on some characteristics and obtain the mean/median value for each group |

Date |
Wed, 19 Jun 2002 11:01:35 +0100 |

Yi, Bingsheng > I wonder whether you will help me figure out the codes to solve the > following problem: > > I have 12 years panel data containing these four variables: Tobin's q, > size, 4-digit industry code (ind4), and id. For each year, I want to make > some adjusments in one variable (Tobin's q) based on the other > two variables > (industry and size). First I need to ensure that there are lat least 10 > firms within each industry. If the number of firms within a > 4-digit industry > code is less than 10, I use 3-digit industry code generated by gen str4 > ind3=substr(ind4,1,3), see whether the number of firms with the > same 3-digit > industry code is greater or equal to 10, if not, then generate and use > 2-digit industry code. So in the end there are at least 10 firms > within an > industry ( which are classified by 4-digit, 3-digit, 2-digit, or 1-digit > industry code). The problem is how to get and record the number > of firms in > each industry. bysort ind4 (size) : gen freq = _N > Then within each industry, I want classify firms into three > groups based on > size, the smallest group contains the smallest 30% firms in size > within that > industry, the middle group contains the middle 40% firms in size (30% to > 70%), and the large group contain firms whose size belongs to the largest > 30% in that industry. Then I get the median or mean value of Tobin's q for > each of these groups within an industry. > > the industry-size adjusted Tobin's q = Tobin's q of a firm in an > industry - > the mean tobin's q of a group to which the firm belongs within the same > industry > > For example, if IBM belongs to the largest size group in computer > industry, > then the industry-size adjusted Tobin's q of IBM is equal to > Tobin's q of IBM - the mean/median value of the largest size group within > the computer industry. > > But I don't know how to generate these groups and obtain the industry-size > adjusted Tobin's q for a sample firm. I will greatly appreciate > your help!!! Within industry, you have sorted on -size- if you use the command above. by ind4 : gen .... if _n <= 0.3 * _N gives the lowest 30%, etc. Nick n.j.cox@durham.ac.uk * * 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: how to generate groups based on some characteristics and obtain the mean/median value for each group***From:*"Yi, Bingsheng" <byi@coba.usf.edu>

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