We are using google alerts in our study to catch and categorize new contents as they happen on the web.
We want to be as comprehensive as possible and catch the more new results for a query is possible.
But we know there are other services at google apart from alerts, like google news.
So, our question is: Is google alert the most complete system so that we can expect that the results from news, blog search, youtube feed will always be a subset of the ones from alert?
Since it's a research study, I'll be grateful if you could also post the source/ref. you base your answers on!