How to calculate p-value for AR model? How to determine significance?

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MC3105
MC3105 2014-10-30
编辑： Roger Wohlwend 2014-10-31
Hello everyone!!
I am using the arima model command to create an AR(2) model. When running the program matlab tells the me value of the t-Statistic for each of the two AR parameters.
How can I tell from the output whether the parameter is significant? Is there a way to calculate the p-value for each of my two AR parameters?
Thanks alot!!

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Roger Wohlwend
Roger Wohlwend 2014-10-31
编辑：Roger Wohlwend 2014-10-31
You don't need the p-values. If the absolute value of the t-statistics is 2 or greater, the coefficient is significant.
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Roger Wohlwend
Roger Wohlwend 2014-10-31
编辑：Roger Wohlwend 2014-10-31
If the degrees of freedom is high enough the t distribution approaches the standard normal distribution. In such a distribution the values between -2 and 2 (twice the standard deviation from the mean) occur approximately in 95 % of the cases. That is why a t-statistics of 2 or greater corresponds to a confidence level of 5 %.
The exact value is not 2 but 1.96. You can calculate it with the following formula:
tstat = norminv(1-confidenceLevel/2,0,1)
The exact formula is
tstat = -tinv(confidenceLevel/2,DegreesOfFreedom)
So if you want a different confidence level than 5 % use the formula above to see what the t-statistics must be.
If you want to calculate the p-value from the t-statistics, use the following formula:
pVal = 2*(tcdf(-abs(tValue), dof));
where tValue is the coefficient divided by its standard deviation and dof is the degrees of freedom.

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