Thursday, July 25, 2013
BT Claim 2: Using more years of data would reduce the earnings premium
Response: Using more years of historical data is as likely to increase the earnings premium as to reduce it
We have doubts about the effect of more data, even if Professor Tamanaha does not.
Without seeing data that would enable us to calculate earnings premiums, we can’t know for sure if introducing more years of comparable data would increase our estimates of the earnings premium or reduce it.
The issue is not simply the state of the legal market or entry level legal hiring—we must also consider how our control group of bachelor’s degree holders (who appear to be similar to the law degree holders but for the law degree) were doing. To measure the value of a law degree, we must measure earnings premiums, not absolute earnings levels.
As a commenter on Tamanaha’s blog helpfully points out:
“I think you make far too much of the exclusion of the period from 1992-1995. Entry-level employment was similar to 1995-98 (as indicated by table 2 on page 9).
But this does not necessarily mean that the earnings premium was the same or lower. One cannot form conclusions about all JD holders based solely on entry-level employment numbers. As S&M's data suggests, the earnings premium tends to be larger during recessions and their immediate aftermath and the U.S. economy only began an economic recovery in late 1992.
Lastly, even if you are right about the earnings premium from 1992-1995, what about 1987-91 when the legal economy appeared to be quite strong (as illustrated by the same chart referenced above)? Your suggestion to look at a twenty year period excludes this time frame even though it might offset the diminution in the earnings premium that would allegedly occur if S&M considered 1992-95.”
There is nothing magical about 1992. If good quality data were available, why not go back to the 1980s or beyond? Stephen Diamond and others make this point.
The 1980s are generally believed to be a boom time in the legal market. Assuming for the sake of the argument that law degree earnings premiums are pro-cyclical (we are not sure if they are), inclusion of more historical data going back past 1992 is just as likely to increase our earnings premium as to reduce it. Older data might suggest an upward trend in education earnings premiums, which could mean that our assumption of flat earnigns premiums may be too conservative. Leaving aside the data quality and continuity issues we discussed before (which led us to pick 1996 as our start year), there is no objective reason to stop in the early 1990s instead of going back further to the 1980s.
Our sample from 1996 to 2011 includes both good times and bad for law graduates and for the overall economy, and in every part of the cycle, law graduates appear to earn substantially more than similar individuals with only bachelor’s degrees.
This might be as good a place as any to affirm that we certainly did not pick 1996 for any nefarious purpose. Having worked with the SIPP before and being aware of the change in design, we chose 1996 purely because of the benefits we described here. Once again, should Professor Tamanaha or any other group wish to use the publicly available SIPP data to extend the series farther back, we'll be interested to see the results.