I'm trying to understand whether the observed time series can be described as a random walk or not.
When I check autocorrelations of the differences, none of the autocorrelation bars for the difference series exceeds the blue dashed thresholds. However, I was not sure whether it was enough, so I've tried the augmented Dickey-Fuller test on the differences. The p-value turned out to be high, so we could not reject the null-hypothesis of stationarity. While on its own, this does not necessarily mean that the difference series is not stationary, it is still confusing. Moreover, my intuition says that there is an increasing trend, but I'm not sure how to describe it.
Start = 1998 End = 2011 Frequency = 1 59 334 333 402 450 461 452 468 461 463 508 573 639 567