I am curious to understand how the tangle has improved in terms of confirmation rate since its inception. Are there any statistics which show this? A positive growth is definitely a good sign. And if the differential of this growth rate is also positive its an even better sign.
The global confirmation rate (ctps) is unfortunately not a good indicator of the healthiness of the tangle. (and I say "unfortunately" because many commentators believe it is).
Why global ctps isn't a good indicator ?
IOTA is a permissionless and feeless network, so it is easy for anyone to setup a node using an unfair tip-selection algorithm, flooding the network with invalid transactions and impacting the ctps negatively. That's exactly what we see today with the "side-tangle".
A good indicator would be the ctps of transactions attached to the tangle using a fair tip-selection algorithm. AFAIK, today it's impossible to compute this kind of indicator accurately (because when looking at a transaction, it's impossible to say (with 100% certainty) what kind of tip-selection algorithm was used to attach it).
You can find some historical data here but it contains data only since Friday, May 18, 2018 4:37:00 PM GMT and keep track of value transaction only.