{smcl} {* 24 Dec 2014}{...} {cmd:help hhi5} {hline} {title:Title} {p2colset 5 14 22 2}{...} {p2col :{hi:hhi5} {hline 2}}generates Herfindahl-Hirschman index (HHI) variables {p_end} {p2colreset}{...} {title:Syntax} {p 4 19 2} {cmdab:hhi5} {varlist} {ifin}, {opth by:(varlist:groupvar)} [ {cmdab:pre:fix:}{cmd:(str)} {cmdab:t:op:}{cmd:(#)} {cmdab:mim:obs:}{cmd:(#)} {opt per:centage} {cmdab:out:file:}{cmd:(str)} {opt replace} {opt noe:xpand} ] {title:Description} {pstd} hhi5 generates Herfindahl-Hirschman index (HHI) variables also commonly known as concentration index in economics and finance. {break} See: {browse "http://baike.baidu.com/view/4362432.htm":http://baike.baidu.com/view/4362432.htm}. The module supports multiple variables and group ids and allows user to export output in table format (csv comma delimited). {title:Options} {phang} {opth by:(varlist:groupvar)} specifies the {it:groupvar} which defines the categories that {opt hhi5} will use to calculate the HHI index. For example, {opt by:(industry)}, {opt by:(industry year)}. {phang} {cmd:prefix(}{it:str}{cmd:)} prefixes new variable names with {it:str}. If {cmd:prefix(}{it:str}{cmd:)} is not specified, the defult prefix is "hhi_". Thus, {bf:hhi5 sale output, options} will generate two variables named as {it: hhi_sale} and {it: hhi_output}, respectively. {phang} {cmd:top(}{it:#}{cmd:)} use firms in each {it:groupvar} with the highest top # values of each variable in {varlist} to calculate the HHI index. {phang} {cmd:minobs(}{it:#}{cmd:)} specifies the minimum number of observations in each of the category defined by {it:groupvar}. {phang} {opt percentage} scale the market share of each firm in category defined by {it:groupvar} to be a percentage of the total, between 0 and 100. The defult is scaled to be a proportion of the total, between 0 and 1. Specify this option cause the HHI index 10^4 times larger. {phang} {opt noexpand} restrict the HHI index values to sub-sample correponding {cmd:top(}{it:#}{cmd:)} or {cmd:minobs(}{it:#}{cmd:)}. The defult is to expand the HHI index values to the full sample. {phang} {cmd:outfile(}{it:filename}{cmd:)} export data in table format (.csv comma delimited), named as {it:filename}.csv. {title:Examples} {result}{dlgtab:The nlsw88 data}{text} {phang2}{inp:.} {stata "sysuse nlsw88,clear":sysuse nlsw88,clear}{p_end} {phang2}{inp:.} {stata "gen sale = ln(wage)":gen sale = ln(wage)}{p_end} {phang2}{inp:.} {stata "hhi5 sale, by(industry)":hhi5 sale, by(industry)}{p_end} {phang2}{inp:.} {stata "hhi5 sale hour, by(industry race) prefix(hhi5) top(5) minobs(10)":hhi5 sale hour, by(industry race) prefix(hhi5) top(5) minobs(10) }{p_end} {phang2}{inp:.} {stata "br industry race hhi*":br industry race hhi*}{p_end} {title:Acknowledgements} {pstd} Codes from {help hhi} by Muhammad Rashid Ansari ({browse "mailto:rashid.ansari@insead.edu":rashid.ansari@insead.edu}) have been incorporated. {p_end} {title:Author} {pstd} {cmd:Yujun,Lian (Arlion)} Department of Finance, Lingnan College, Sun Yat-Sen University, China.{break} E-mail: {browse "mailto:arlionn@163.com":arlionn@163.com}. {break} Blog: {browse "http://blog.cnfol.com/arlion":http://blog.cnfol.com/arlion}. {break} Homepage: {browse "http://www.lingnan.sysu.edu.cn/lnshizi/faculty_vch.asp?name=lianyj":http://www.lingnan.sysu.edu.cn/lnshizi/faculty_vch.asp?name=lianyj}. {break} MyCourse: {browse "http://www.peixun.net/author/3.html":http://www.peixun.net/author/3.html}. {break} Youku Videos: {browse "http://i.youku.com/arlion":http://i.youku.com/arlion}. {break} {p_end} {title:Also see} {pstd} Online: {manhelp egen R}; {help hhi} {p_end} {pstd} {p_end}