This paper uses the American Community Survey to examine the previously overlooked fact that foreign STEM (science, technology, engineering, and mathematics) graduates have much lower self-employment rates than their non-STEM counterparts, with an unconditional difference of 3.3 percentage points.
In that sample, the unconditional difference is higher, 6%, but is considerably reduced and becomes insignificant after controlling for personal characteristics.
We can use this information in similar fashion to obtain rough, unconditional, difference-in-differences estimates of the impact of activation on the probability of completing an episode by a certain date.
The corresponding unconditional difference-in-differences estimates for PPS and PPP recipients are a reduction of 15% in mean PPS episode duration (see Table 3) and a reduction of 49% in mean PPP episode duration (see Table 4).
The corresponding unconditional difference-in-differences estimate is therefore that activation has led to or has coincided with a reduction in mean duration of completed PP episodes, for those covered by the new requirements, of 31%.
But by comparing the change in mean durations of completed episodes, before and after 1st July 2007 for the two age groups, we can get a simple unconditional difference-in-differences estimate of the impact of activation on completed PP episode duration.
The summary statistics and the unconditional difference-in-differences estimates in Tables 2 and 3 indicate that the main individual characteristics of both groups did not change substantially before and after the policy change, but the household characteristics of both groups changed a lot.
On balance the suggestion from both the simple unconditional difference-in-differences estimates and the KM hazard plots is that the 2007 reforms coincided with a relative increase in the hazard rate for exiting PP for those covered by the new requirements, both to other IS payments and exiting IS altogether, and for both PPS and PPP recipients.
A similar unconditional difference-in-differences estimate of the impact of activation on episode duration including right-censored episodes, where the right-censoring date is treated as the end date, suggests duration falls by 36% for those covered by the new participation requirements.
We prove that well posedness, that is, maximal regularity of (1.2) in vector-valued spaces, is characterized on Banach spaces having the unconditional martingale difference property ( see, e.g., [4]) by the -boundedness of the set (1.3).
As applications, we get the optimal order of the unconditional Martingale differences (UMD -constants of the Schatten class Sp when p→∞.
