Following up from my previous post, I thought it would be interesting to break down the ages of congresspersons by party. The data used in this post are the same set scraped from the Biographical Directory of the United States Congress.

The plot below shows the evolution of age over time for Republicans and Democrats in congress (other parties had insufficient representation to build useful statistics). The lines are median values and the lower and upper shaded regions represent the 25th and 75th percentiles, respectively. Over much of the last 150 years, the median age of congresspersons has been comparable across the two major political parties, with Democrats tending slightly younger. However, since 2000 there has been a sharp increase in the age of Democrats in congress, the median age rising from 56 in 2000 to a 63 in 2016. For comparison, The ages of Republicans showed a much more modest increase from 56 to 58 years.

Ages of Democratic and Republican Congresspersons over time

The next natural question to ask is what is causing Democrats to tend so old over the last 17 years? Has there been an influx of geriatric fresh meat or, rather, just the old guard refusing to give up their seats? To attempt to answer this, I found the distribution of number of years served in congress (inclusive of both house and senate stints) and, again, found median and quartile values. The results are shown below.

Career Lengths of Republicans and Democrats over time

And, indeed, what we find is that the median career length for Democrats has skyrocketed since 2000 where it was 9.5 years to a staggering 15.1 years in 2012 before tapering off to 11.3 in 2016. But these are just median numbers, the 75th percentile for Democrats in 2016 was just a hair under 23 years, meaning a full quarter of Democratic congresspersons have served for 23 years or more. The Republicans have followed a similar, albeit less volatile, trajectory since 2000 where they started 9.1 years before peaking at 13 in 2008 and then falling since to 7.4 in 2016. The 75th percentile for Republicans in 2016 was 15.1 years which is nearly eight years fewer than their Democratic colleagues.

If one takes a more long-sighted approach, however, the apparent trend is clearly that congresspersons are serving for longer and longer before retiring. Surely some part of this is simply due to the fact that they are living longer and healthier lives. It's plausible that another component may be increasing financial and political obstacles that prevent new people from running, but this is just speculation.

Another point that can be gleaned from the above plot is the presence of sudden and dramatic rises and falls in both parties median career lengths. A better student of history than I could probably look at each of these and tell you all about the political tides of the last 150 years and point out the causes of each of these spikes, but suffice to say that it seems when a party gets kicked out, it gets kicked out hard.

Have feedback, questions, ideas for further research? Hit me up on twitter or shoot me an email at caleb @ this domain.