# I have two time series recorded on a weekly basis that have a quadratic trend. Should I difference the series twice with lag 1?

I have two time series on google Trends weekly data for the search of the terms 'machine learning' and 'data science'. The data can be found here http://www.filehosting.org/file/details/524910/dataScience.csv

Here's a plot of the time series in levels: I'm not sure whether differencing the series twice is enough for ensuring stationarity.

The Augmented Dickey Fuller test (CADFtest command in R) shows that both time series are stationary when I difference them twice.

Augmented DF test