The files credit contain 921 observations for 2005 for US firms' credit
ratings, including a set of firm characteristics. The data are taken from
Compustat. 

The following variables are available:
booklev:  ratio of book value of debt / assets
marklev:  ratio of market value of debt / assets
ebit:     earnings before interest and taxes / total assets
invgrade: dummy, 1 if investment grade, 0 if speculative grade
logsales: log firm sales
rating:   credit rating, from 1 (low) to 7 (high)
reta:     retained earnings / total assets
wka:      working capital / total assets

Note: marklev is not used in Section 7.2.3.

Descriptive statistics: 


    Variable |       Obs        Mean    Std. Dev.       Min        Max
-------------+--------------------------------------------------------
     booklev |       921    .2931868    .1735339          0   .9992067
        ebit |       921    .0938921    .0843643  -.3841692   .6515085
    invgrade |       921    .4723127    .4995041          0          1
    logsales |       921    7.995754    1.497413   1.100278   12.70142
     marklev |       921    .2547287    .1879701          0   .9648595
-------------+--------------------------------------------------------
      rating |       921    3.499457    1.134561          1          7
        reta |       921    .1569942     .300684  -.9958922   .9799219
         wka |       921    .1404142    .1503398  -.4120839   .7480223