Next Candidate to Announce will be Monday or Tuesday

So, candidates are forming exploratory committees, few are formally announcing. Keeping track of the date an exploratory committee was announced or (if the candidate just filed without forming a committee) the date of FEC filing. The data accumulated so far:

Candidate	Announced
Elizabeth Warren	December 31, 2018[cnn]
Tulsi Gabbard	January 11, 2019[fec]
Julian Castro	January 12, 2019[bloomberg.com]
Kirsten Gillibrand	January 15, 2019[nytimes]
Kamala Harris	January 21, 2019[fec]
Pete Buttigieg	January 23, 2019[politico]
Cory Booker	February 1, 2019[fec]
Amy Klobuchar	February 10, 2019
Bernie Sanders	February 19, 2019[fec]
Jay Inslee	March 1, 2019[fec]
John Hickenlooper	March 4, 2019[fec]
Beto O'Rourke	March 14, 2019[fec]
Mike Gravel	March 19, 2019[nbc]
Tim Ryan	April 4, 2019[nbc]
Eric Swalwell	April 8, 2019[fec]

I goofed on thinking Ojeda was the start of the primary process, Senator Warren seems like the opening candidate.

The questions that spring to mind include:

1. How many people will qualify for the June debates?
2. Are the Democratic candidates similar in announcement behaviour as past Republican candidates?
3. When will the next announcement be?

I will dig through the first two questions in a future blog post, but the third question is time sensitive. The short answer is we can expect the next candidate to emerge Monday night or Tuesday morning, the exact probability distribution is plotted below:

This is based on the Jeffreys prior for predicting the exponential distribution using the prior candidates in this cycle as the data points (c.f., [wikipedia]). The expected number of days after the Swalwell's announcement is 98/13 ≈ 7.53846.

I'll "show my work" in a future blog post, and include a "DIY" equation to predict the next announcement based on N candidates already announced and d (the number of days between the latest candidate and the first, Elizabeth Warren's announcement date).

Addendum April 23, 2019 at 6:27 am (PDT). Representative Seth Moulton (D-MA, 6) was the next candidate to announce he was running for president, throwing his hat in the ring on April 22, 2019: a full week after expected. The probability of this happening, with the Bayesian posterior used here, is approximately 1.927626% whereas the maximum likelihood estimate would give 1.93336%; however we cut it, it's around 1.93% probability. (I forgot to publish this addendum on the date I wrote it, it was saved as a draft for about a month.)

(After further thought, Moulton declared \(2/\lambda\) days after the previous candidate, with \(\lambda=13/98\approx 1/7.5\). The probability of a candidate declaring after twice the expected value in an exponentially distributed model is \(\Pr(x\geq 2/\lambda)\approx 0.13533\) which isn't unreasonable. An event occurring with 13.5% probability is roughly the same odds as getting 3 heads in a row with a fair coin.)