$1\mathrm{.}3$ Regression analysis can be used to test whether the market efficiently uses information in valuing stocks. Let return be the total return from holding a firm's stock over the four$-$year period from the end of $1990$ to the end of $1994.$ For $1990,$ let $dkr$ be a firm's debt to capital ratio, let eps denote the earnings per share, let netinc denote net income, and let salary denote total compensation for the CEO.

Using the data in RETURN, the following equation was estimated:

widehat$($ return $)=-14\mathrm{.}37\mathrm{.}321dk{r}_{(6\mathrm{.}89)}{\mathrm{.}043}_{(\mathrm{.}201)}$ eps $-{\mathrm{.}0051}_{(\mathrm{.}078)}$ nentinc ${\mathrm{.}0035}_{(\mathrm{.}0047)}$ salary

$n=142,R^2=\mathrm{.}0395$

Test whether the explanatory variables are jointly significant at the $5\%$ level. Is any explanatory variable individually significant? $[7]$