Can we force the fitting coefficient be less than zero?

[wutao9999]

In linear regression, can we possibly force the fitting coefficient be less than zero?

I am doing some analysis for price elasticity, a larger-than-zero-coefficient is usually doesn't make sense.  This is the reason I am asking if we can force the fitting result of coefficient be less than zero.

Thank you.

[PaigeMiller]

I think you can do the regression in PROC CALIS (the docs give an example) and use the BOUNDS statement to force the coefficient to be less than zero.