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i need to write the ARIMA equation but i have a question about drift

fit = Arima(price, order = c(1,1,0),include.drift = TRUE)

These is result

  Series: price 
ARIMA(1,1,0) with drift 

Coefficients:
         ar1   drift
      0.3618  0.9272
s.e.  0.1452  1.2564

sigma^2 estimated as 34.55:  log likelihood=-161.74
AIC=329.49   AICc=330   BIC=335.28



z test of coefficients:

      Estimate Std. Error z value Pr(>|z|)  
ar1    0.36185    0.14518  2.4925  0.01269 *
drift  0.92723    1.25644  0.7380  0.46053  
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Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

when hypothesis test with P-value the drift is not significant

Question

When do I write ARIMA equation,I must write drift in equation ?

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Standard arima software requires that the drift parameter MUST be included if there is no differencing incorporated otherwise it is optional. I have seen and used software where drift is ALWAYS an option.

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