Don't get caught up in the details. The overarching issue is, there is a gap (however large) and you can do something about it.
Here is a periodical to the original study:
Here is a link to a great summary article about the famous study if you are crunched for time:
Yes, quality and quantity matter equally, when they are not equal, we can put more time in to building one up and have a lasting impact on the life of a child...just by saying a few more words (Ok, 30-million is more than a few). Start with a few added words or a couple of novel words per day and you will get there before you know it...you can do this!