Hey everyone,

Really need urgent help here.

I am trying to determine if the change in the slope of a line (beta) is statistically significant due to a particular event. As such, how do you test if the slope of line A is statistically different from the slope of line B?

For instance, let's say i'm investigating the beta of Apple's stock, when regressed against the S&P 500.

Regression 1 - 2005-2006 (24 monthly observations), Beta = 0.8

Regression 2 - 2007-2009 (36 monthly observations), Beta = 0.5 (decrease)

How do I determine if this change in beta is statistically different over the two different time periods? Do I apply a t-test? If so, what's the formula to do so?

(I have also deliberately used 2 different sample sizes for the 2 regressions. Please highlight to me if this affects the statistical testing.)

Also, I've noticed that the t-test has always been applied to means or proportions, but never to the slope (beta). As such, is there something wrong with my concept or use of terminologies? Hope you experts can clarify this with me. I really need your help! Thanks in advance everyone

Really need urgent help here.

I am trying to determine if the change in the slope of a line (beta) is statistically significant due to a particular event. As such, how do you test if the slope of line A is statistically different from the slope of line B?

For instance, let's say i'm investigating the beta of Apple's stock, when regressed against the S&P 500.

Regression 1 - 2005-2006 (24 monthly observations), Beta = 0.8

Regression 2 - 2007-2009 (36 monthly observations), Beta = 0.5 (decrease)

How do I determine if this change in beta is statistically different over the two different time periods? Do I apply a t-test? If so, what's the formula to do so?

(I have also deliberately used 2 different sample sizes for the 2 regressions. Please highlight to me if this affects the statistical testing.)

Also, I've noticed that the t-test has always been applied to means or proportions, but never to the slope (beta). As such, is there something wrong with my concept or use of terminologies? Hope you experts can clarify this with me. I really need your help! Thanks in advance everyone

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