> Can anyone explain why "in spite of" would have a higher frequency than
> "in spite" in the following graph from Google ngrams?
?What the y-axis shows is this: of all the bigrams contained in our sample of books written in English and published in the United States, what percentage of them are [the bigram sought]??
In other words: the frequencies are calculated over the total number of N-grams of the same length. Since the denominator in the calculation changes, a bigram and trigram that are expected to have almost identical distributions over the corpus (as in your example) can show slight differences in calculated frequency. (I suspect rounding errors play a role as well.)