I've got 36 months of timeseries data, and eyeballing it, it has a linear trend upward. I wanted to do a little more than just eyeball it though. So I put together a correlogram of autocorrelation values for lags 1 to 12 on my observations. They're all positive. Would you say that's good evidence that I've got a linear trend?
See a picture of my autocorrelations here.
And would that spike back up at the end there likely be due to some seasonality (that'd make total sense for my business's data...we do heavy sales at Xmas and Valentines day)?