How to interpret Whited Wu index (WW-index) I want to study financial constraints on companies of different groups and for that I try to use Whited-Wu index:
WW = - 0.091CF - 0.062DIVPOS + 0.021*TLTD - 0.044*LNTA + 0.102*ISG - 0.035*SG
Where TLTD is the ratio of the long-term debt to total assets; DIVPOS is an indicator that takes the value of one if the firm pays cash dividends; SG is firm sales growth; LNTA is the natural log of total assets; ISG is the firm’s three-digit industry sales growth; CASH is the ratio of liquid assets to total assets; CF is the ratio of cash flow to total assets (see Whited and Wu. Financial Constraints Risk. 2006).

Although I managed to compute it, I have difficulties with results interpretation. My idea was to compare different companies/groups of firms using this index. As written in one of the papers, "higher index values can be associated to higher need of external capital". So if in 2010, for "Toyota" I got value -0.9 and for "Fuji Technica Inc." -0.53, may I conclude that Toyota is more financially constrained (requires more external capital)? Similarly, if I get two industries - food and car producing - then the first have higher values of WW.
This is equation $(13)$ of Whited, T. M., &amp; Wu, G. (2006). Financial constraints risk. Review of Financial Studies, 19(2), 531-559.

It is empirically estimated as regards the specific coefficient values. The important question is, 


  What is the left-hand-side?


Looking at eq. $(12)$ of the paper the left-hand-side of $(13)$ is $\lambda_{i,t+1}$ which in turn is part of

$$\Lambda_{i,t+1} = \frac {1+\lambda_{i,t+1}}{1+\lambda_{i,t}}$$

$\Lambda_{i,t+1}$ is discussed in the middle of p. 536 (between eq. 5 and eq. 6). As the authors write,


  If the outside equity constraint is binding, the effects of external
  finance constraints show up in the term $\Lambda_{i,t+1} =
 (1+\lambda_{i,t+1})/(1+\lambda_{i,t})$, which is the relative shadow
  cost of external finance. In the absence of finance constraints,
  $\Lambda_{i,t+1}=1$. On the other hand, if the equity constraint
  binds, then generally $\Lambda_{i,t+1}\neq1$, unless $\lambda_{i,t+1}
 = \lambda_{i,t}$. As also noted in Gomes, Yaron, and Zhang (2004), this last observation implies that finance constraints can only affect
  investment if they are time varying. It is the shadow value of the
  constraint today, relative to tomorrow, that is important.


So $\lambda_{i,t+1}$ is the shadow cost of external finance at period $t+1$. Near the end of p. 538 the authors write


  The higher $\lambda_{i,t+1}$, the greater is the effect of finance
  constraints.


This is translated as "the higher $\lambda_{i,t+1}$, the more difficult (or costly) is for a firm to obtain external financing". It does not appear to relate to whether it needs more external financing or not.

Moreover, as the authors write in p. 540, it being a shadow value, it must be non-negative. So what do you make of the fact that you obtained negative values?