PERSPECTIVES: How Common is "Parking" among Social Security Disability Insurance Beneficiaries? Evidence from the 1999 Change in the Earnings Level of Substantial Gainful Activity

by Jody Schimmel, David C. Stapleton, and Jae Song
Social Security Bulletin, Vol. 71, No. 4, 2011

Appendix

Table A-1. DD estimates for the impact of the 1999 SGA earnings-level increase on average monthly from the TWP completion year to the second post-TWP year for the 1996 and 1998 completer cohorts: Full regression results corresponding to Table 4
Characteristic	Nominal TWP-year earnings category ($)
	0–199		200–499		500–699		700–999		1,000 or more
	Parameter estimate	Standard error	Parameter estimate	Standard error	Parameter estimate	Standard error	Parameter estimate	Standard error	Parameter estimate	Standard error
DD estimate	-0.0054	0.0036	-0.0048	0.0036	0.0220	0.0025	-0.0022	0.0024	-0.0096	0.0035
Indicator for 1998 TWP completer cohort	0.1928	0.0027	-0.1422	0.0027	-0.0457	0.0019	-0.0378	0.0017	0.0330	0.0026
Indicator for second post-TWP year	-0.0146	0.0022	-0.0250	0.0028	-0.0015	0.0019	0.0051	0.0018	0.0360	0.0024
Age (years, as of December 31)	0.0021	0.0001	0.0007	0.0001	-0.0005	0.0001	-0.0012	0.0001	-0.0011	0.0001
Male	0.0082	0.0018	-0.0426	0.0019	-0.0081	0.0013	-0.0043	0.0012	0.0468	0.0018
Black	-0.0236	0.0052	-0.0012	0.0051	0.0249	0.0035	0.0230	0.0034	-0.0232	0.0051
Hispanic	0.0876	0.0068	-0.0539	0.0062	-0.0014	0.0044	0.0001	0.0042	-0.0323	0.0063
Other race	-0.0119	0.0113	-0.0312	0.0105	0.0012	0.0075	-0.0004	0.0071	0.0424	0.0115
White	-0.0297	0.0049	0.0235	0.0048	0.0077	0.0033	-0.0009	0.0031	-0.0006	0.0048
Education (years)
0–8	0.0489	0.0051	-0.0204	0.0049	0.0028	0.0035	0.0085	0.0032	-0.0397	0.0043
9–11	0.0245	0.0033	-0.0259	0.0033	0.0045	0.0024	0.0172	0.0023	-0.0203	0.0031
12	-0.0041	0.0021	-0.0098	0.0022	0.0013	0.0015	0.0064	0.0014	0.0063	0.0021
13–15	-0.0241	0.0033	-0.0379	0.0033	-0.0022	0.0024	0.0020	0.0022	0.0623	0.0036
16 or more	-0.0434	0.0038	-0.0767	0.0037	-0.0154	0.0026	-0.0055	0.0025	0.1409	0.0044
Primary disabling condition
Major affective disorders	0.0872	0.0165	-0.0023	0.0178	-0.0292	0.0137	-0.0115	0.0124	-0.0442	0.0187
Schizophrenia and psychoses	0.1130	0.0167	0.1045	0.0180	-0.0202	0.0138	-0.0250	0.0125	-0.1724	0.0187
Anxiety and neurotic disorders	0.0806	0.0171	-0.0010	0.0184	-0.0225	0.0141	0.0014	0.0128	-0.0584	0.0192
Other mental disorders	0.0556	0.0169	0.0675	0.0183	-0.0136	0.0140	-0.0097	0.0126	-0.0999	0.0190
Mental retardation	0.0448	0.0165	0.2143	0.0179	-0.0007	0.0138	-0.0307	0.0124	-0.2278	0.0186
Back disorders	0.0797	0.0168	-0.0560	0.0180	-0.0400	0.0139	-0.0122	0.0125	0.0285	0.0190
Musculoskeletal system	0.0663	0.0169	-0.0099	0.0182	-0.0314	0.0139	-0.0188	0.0126	-0.0062	0.0191
Infectious and parasitic diseases	0.0637	0.0225	0.0415	0.0239	-0.0150	0.0176	-0.0240	0.0154	-0.0663	0.0239
HIV/AIDS	0.0323	0.0173	-0.0208	0.0185	-0.0282	0.0143	-0.0133	0.0129	0.0300	0.0197
Neoplasms	-0.0343	0.0171	-0.1423	0.0182	-0.0646	0.0140	-0.0217	0.0128	0.2628	0.0197
Endocrine/nutritional	0.0845	0.0173	-0.0156	0.0185	-0.0331	0.0142	-0.0041	0.0129	-0.0317	0.0194
Blood/blood-forming diseases	0.0313	0.0212	-0.0486	0.0222	-0.0473	0.0167	-0.0184	0.0158	0.0830	0.0246
Severe visual impairment	0.0438	0.0181	-0.0523	0.0191	-0.0093	0.0149	0.0593	0.0140	-0.0414	0.0202
Severe hearing impairment	0.0356	0.0175	-0.0006	0.0189	-0.0052	0.0146	0.0043	0.0132	-0.0341	0.0197
Severe speech impairment	0.0569	0.0350	-0.0294	0.0344	-0.0496	0.0236	-0.0187	0.0232	0.0408	0.0386
Nervous system	0.0618	0.0169	0.0450	0.0182	-0.0199	0.0140	-0.0189	0.0126	-0.0679	0.0190
Circulatory system	0.0582	0.0171	-0.0106	0.0184	-0.0210	0.0141	-0.0137	0.0127	-0.0130	0.0193
Respiratory system	0.0591	0.0190	0.0114	0.0203	-0.0174	0.0153	-0.0132	0.0138	-0.0399	0.0209
Digestive system	0.0265	0.0186	-0.0796	0.0194	-0.0593	0.0146	-0.0078	0.0137	0.1201	0.0213
Genitourinary system	0.0259	0.0174	-0.0426	0.0186	-0.0343	0.0143	-0.0196	0.0130	0.0706	0.0199
Skin/subcutaneous tissue	0.1233	0.0288	-0.0435	0.0275	-0.0264	0.0210	-0.0204	0.0189	-0.0330	0.0293
Congenital anomalies	0.0396	0.0228	0.1865	0.0259	0.0010	0.0190	-0.0476	0.0154	-0.1796	0.0229
Injuries	0.0361	0.0168	-0.0561	0.0181	-0.0391	0.0139	-0.0209	0.0126	0.0800	0.0191
Other	0.0505	0.0164	0.0106	0.0177	-0.0186	0.0137	-0.0013	0.0123	-0.0412	0.0186
TWP completion month
January	0.0256	0.0046	-0.0571	0.0045	-0.0100	0.0032	-0.0137	0.0030	0.0553	0.0045
February	0.0110	0.0045	-0.0479	0.0045	-0.0142	0.0032	-0.0130	0.0030	0.0640	0.0044
March	0.0028	0.0044	-0.0467	0.0045	-0.0060	0.0032	-0.0089	0.0030	0.0589	0.0044
April	-0.0073	0.0044	-0.0462	0.0044	-0.0051	0.0032	-0.0091	0.0030	0.0678	0.0044
May	-0.0146	0.0042	-0.0361	0.0043	-0.0064	0.0031	-0.0075	0.0029	0.0645	0.0042
June	-0.0188	0.0043	-0.0377	0.0044	-0.0026	0.0031	0.0001	0.0030	0.0589	0.0043
July	-0.0157	0.0044	-0.0362	0.0046	-0.0008	0.0033	-0.0020	0.0031	0.0548	0.0044
August	-0.0185	0.0044	-0.0231	0.0046	0.0007	0.0033	0.0015	0.0031	0.0394	0.0044
September	0.0457	0.0039	0.0142	0.0040	-0.0147	0.0027	-0.0167	0.0026	-0.0285	0.0036
October	-0.0053	0.0044	-0.0061	0.0046	-0.0010	0.0032	-0.0033	0.0030	0.0156	0.0042
November	-0.0050	0.0043	-0.0073	0.0045	0.0002	0.0032	-0.0057	0.0030	0.0177	0.0042
Intercept	0.0501	0.0177	0.3611	0.0190	0.1656	0.0145	0.1663	0.0132	0.2570	0.0197
Number of observations	233,930		121,492		28,678		25,632		58,128
Adjusted R-squared	0.0593		0.0656		0.0071		0.0098		0.0655
SOURCE: SSA's 2007 TRF data merged with MEF data.
NOTE: Omitted categories from the regression model include missing race, missing primary disabling condition, missing education status, and TWP completion month in December.

Table A-2. DD estimates for the impact of the 1999 SGA earnings-level increase on mean monthly earnings from the TWP completion year to the second post-TWP year, by earnings interval in the TWP completion year, for the 1996 and 1998 TWP completer cohorts: Full regression results corresponding to Table 5
Characteristic	Nominal TWP-year earnings category ($)
	Overall		Less than 500		500–699		700–999		1,000 or more
	Parameter estimate	Standard error	Parameter estimate	Standard error	Parameter estimate	Standard error	Parameter estimate	Standard error	Parameter estimate	Standard error
DD estimate	3.8866	11.6592	15.9866	5.3707	17.2542	11.7817	18.4906	17.2946	-7.6915	39.7519
Indicator for 1998 TWP completer cohort	62.5372	6.2975	5.1518	1.3149	5.1965	1.5006	9.2910	2.2142	-10.1234	18.9262
Indicator for second post-TWP year	44.0383	9.3631	98.6104	4.1510	29.2846	8.4781	36.2898	12.5746	-73.2292	34.4259
Age (years, as of December 31)	1.6058	0.2734	-2.4292	0.1284	-4.0616	0.3218	-3.9092	0.4539	17.5550	0.8874
Male	172.5406	5.7616	0.1783	2.7412	13.6061	6.1874	13.7430	9.2567	348.3814	18.0406
Black	-129.0092	31.9313	32.1964	7.1384	-20.4002	16.6308	-34.0154	25.7186	-416.3763	114.2753
Hispanic	-205.8652	33.4989	-69.5298	8.3585	-9.5389	20.6536	-8.6954	31.5295	-374.2935	117.6089
Other race	80.5293	46.4551	-12.9934	14.9064	-46.5146	31.7408	43.0093	55.7919	2.3408	140.6085
White	-43.3134	32.5433	25.7355	6.8306	-16.5007	16.0853	-2.3386	25.2879	-194.5046	116.6975
Education (years)
0–8	-133.6716	11.8063	-33.4089	4.8667	-12.8438	14.2579	-78.4738	18.2650	-265.6697	48.9207
9–11	-89.2504	7.4623	-10.9616	4.0758	-33.1984	9.1836	-46.3559	12.9199	-261.8110	25.2157
12	5.5262	7.0415	-0.8182	3.1169	3.3928	7.1784	-22.5658	10.6072	-43.6796	23.2824
13–15	150.0496	10.3071	27.6498	5.6339	44.1180	12.3871	26.5202	16.0836	135.0863	25.6982
16 or more	572.3826	20.8756	71.0925	11.0502	67.5711	17.7457	61.6534	22.6099	746.2536	44.2387
Primary disabling condition
Major affective disorders	-40.9460	38.2088	9.1347	20.2610	-89.1764	56.0137	-57.0047	66.0713	101.0549	84.9935
Schizophrenia and psychoses	-354.2219	37.8175	-30.3048	19.4290	-170.9595	55.7803	-129.8439	64.9280	-257.0454	86.7720
Anxiety and neurotic disorders	-83.8368	40.3023	-0.3623	20.3839	-80.3719	57.7183	-28.6832	66.5758	54.0168	96.9753
Other mental disorders	-161.8322	38.6253	-3.6513	19.7593	-147.3341	56.1442	-82.0815	65.8156	-0.7567	88.2418
Mental retardation	-387.2097	37.4753	-12.5732	19.2890	-153.8104	55.3318	-137.4609	64.1344	-308.4275	85.8993
Back disorders	128.4055	43.0494	-2.3513	20.2472	-98.7899	56.8886	-10.7327	69.2368	211.2670	99.8006
Musculoskeletal system	34.6109	39.6684	13.7045	21.2740	-80.9971	59.7504	-30.5887	67.4419	135.7998	88.1016
Infectious and parasitic diseases	-105.0050	53.8016	-2.9983	25.5381	-82.9596	75.8870	-112.5069	98.3791	53.5063	134.5186
HIV/AIDS	184.5564	44.8256	43.7924	23.5558	-74.7737	59.6220	-20.4006	70.1392	309.5777	99.8930
Neoplasms	958.6451	53.3380	57.4691	26.2065	50.9550	63.1949	107.0015	72.9602	889.1284	100.9001
Endocrine/nutritional	-42.9501	40.1781	-3.5354	20.6404	-97.9509	57.7633	-39.0733	67.2694	61.0255	92.1967
Blood/blood-forming diseases	463.7903	75.1694	22.5105	34.5133	-99.8819	73.1534	-9.7780	89.1374	799.5738	162.5179
Severe visual impairment	-68.4195	41.5947	-9.4573	21.7428	-40.1478	58.9789	-24.9684	66.9748	55.4097	97.2393
Severe hearing impairment	-57.9384	39.8701	48.9564	22.0228	-74.1816	61.5778	-5.1546	68.7856	-91.4302	89.2821
Severe speech impairment	54.3205	87.9516	8.9965	44.4032	-156.6640	81.5279	93.7077	34.4024	20.1016	194.9995
Nervous system	-47.8123	45.4254	4.8625	19.9173	-133.9343	56.6584	-38.2057	66.3530	306.8841	129.7971
Circulatory system	47.7596	40.9301	-1.6673	20.2633	-93.4275	57.7040	-49.9544	68.3519	160.0718	92.0725
Respiratory system	-8.2694	50.8713	13.1909	23.7228	-98.2870	61.8202	-44.7192	73.7429	195.9551	141.6386
Digestive system	451.0666	54.3847	24.3395	29.4452	5.7970	72.6930	-48.5661	75.3266	546.2329	109.8123
Genitourinary system	252.1342	43.2640	14.4115	21.6954	-58.7977	59.6275	-0.4348	69.1857	407.8473	93.8453
Skin/subcutaneous tissue	-57.6844	62.9407	-25.2792	33.5316	-137.9435	100.5433	59.7690	49.9449	40.2684	151.6898
Congenital anomalies	-303.0858	46.6541	-8.0281	23.7773	-145.7737	66.1756	-125.0023	8.9854	-0.1141	156.5348
Injuries	250.9805	39.9722	19.6082	20.7594	-62.7332	57.7010	71.1137	68.7173	330.5153	86.4934
Other	-59.2039	37.6178	20.0622	19.3356	-63.0866	55.4150	-24.0432	63.9009	17.5271	83.1404
TWP completion month
January	102.9451	17.1940	-64.5378	5.9937	-59.8878	14.5034	-98.6031	20.6147	27.2923	76.8734
February	127.7342	20.1746	-59.9759	5.8593	-62.4709	16.6615	-86.7749	21.8496	18.3566	84.2944
March	108.2659	16.5926	-54.3847	6.0666	-65.3751	14.3197	-115.0781	18.4321	-17.0366	73.9765
April	131.5672	16.7258	-49.7944	5.7252	-71.2574	14.1684	-88.9445	20.6604	-35.6380	74.7174
May	147.0056	16.4089	-39.6249	5.8072	-38.0231	14.1417	-107.7016	19.1058	6.1093	73.9084
June	121.1597	16.4305	-41.1944	6.0936	-64.5903	14.1988	-70.3646	24.8940	-64.7611	74.6442
July	118.1110	16.7243	-28.1850	6.3087	-75.8079	13.4365	-97.3134	18.9568	-32.7231	75.5382
August	81.5598	16.5385	-19.6110	6.4428	-45.9465	14.7548	-63.2083	19.4302	-62.0353	76.1947
September	-82.5369	15.6628	-53.0679	6.1563	-45.2542	12.9009	-64.5756	19.8421	-48.1222	77.0632
October	29.0923	16.5122	-22.0641	6.7304	-12.0151	16.2251	-62.5163	20.9795	-102.1910	77.2100
November	16.1391	16.0215	-13.3835	5.8052	-13.3883	14.1021	-34.7147	19.6629	-90.1469	76.3673
Intercept	634.2349	52.9953	355.2670	21.4314	890.0394	58.3915	1,109.1490	70.1256	1,244.3165	176.6289
Number of observations	233,930		121,492		28,678		25,632		58,128
Adjusted R-squared	0.0504		0.0217		0.0151		0.0109		0.0391
SOURCE: SSA's 2007 TRF data merged with MEF data.
NOTE: Omitted categories from the regression model include missing race, missing primary disabling condition, missing education status, and TWP completion month in December.

Table A-3. DD estimates for the impact of the 1999 SGA earnings-level increase on the number of NSTW months from the TWP completion year to the second post-TWP year, by earnings interval in the TWP completion year, for the 1996 and 1998 TWP completer cohorts: Full regression results corresponding to Table 6
Characteristic	Nominal TWP-year earnings category ($)
	Overall		Less than 500		500–699		700–999		1,000 or more
	Parameter estimate	Standard error	Parameter estimate	Standard error	Parameter estimate	Standard error	Parameter estimate	Standard error	Parameter estimate	Standard error
DD estimate	-0.1314	0.0317	-0.2946	0.0312	-0.6312	0.0858	-0.2244	0.1028	0.0265	0.0704
Indicator for 1998 TWP completer cohort	0.0973	0.0118	0.0448	0.0090	-0.0598	0.0304	-0.0252	0.0372	0.0330	0.0251
Indicator for second post-TWP year	2.6208	0.0235	1.5796	0.0234	2.7910	0.0653	3.5870	0.0772	4.5341	0.0544
Age (years, as of December 31)	-0.0228	0.0008	-0.0186	0.0008	-0.0353	0.0022	-0.0262	0.0028	-0.0144	0.0020
Male	0.2840	0.0163	0.2172	0.0158	-0.0479	0.0438	-0.2274	0.0536	0.0410	0.0370
Black	-0.0701	0.0457	-0.0190	0.0472	0.0704	0.1291	-0.1092	0.1490	-0.2063	0.0980
Hispanic	0.1272	0.0583	0.4507	0.0640	0.1441	0.1642	-0.1698	0.1859	-0.0678	0.1264
Other race	0.3734	0.1044	0.1740	0.1135	-0.0626	0.2954	0.1883	0.3322	0.3438	0.1955
White	-0.1433	0.0433	-0.2144	0.0445	-0.1658	0.1246	-0.0980	0.1433	-0.0268	0.0905
Education
0–8	-0.0816	0.0409	0.0800	0.0398	0.1652	0.1116	-0.2089	0.1390	-0.1620	0.1097
9–11	-0.0323	0.0281	0.1126	0.0288	-0.1226	0.0712	-0.0340	0.0876	-0.3163	0.0685
12	0.0667	0.0192	0.0469	0.0188	-0.0169	0.0514	-0.0041	0.0612	-0.0350	0.0424
13–15	0.3908	0.0316	0.1986	0.0335	0.1727	0.0844	0.1558	0.0983	0.1212	0.0598
16 or more	0.7806	0.0384	0.3994	0.0442	0.3773	0.1124	-0.1111	0.1224	0.2256	0.0626
Primary disabling condition
Major affective disorders	0.0208	0.1619	-0.0100	0.1796	-0.0349	0.3946	0.2386	0.4835	0.5437	0.3572
Schizophrenia and psychoses	-0.8816	0.1624	-0.4985	0.1794	-0.2658	0.3980	0.1561	0.4889	0.2527	0.3654
Anxiety and neurotic disorders	0.0228	0.1669	0.0088	0.1846	0.1474	0.4094	0.5129	0.4976	0.4435	0.3696
Other mental disorders	-0.3965	0.1646	-0.2740	0.1817	-0.4417	0.4015	0.1394	0.4938	0.4684	0.3670
Mental retardation	-1.2869	0.1614	-0.6458	0.1788	-0.6342	0.3944	0.0335	0.4876	0.4694	0.3724
Back disorders	0.6413	0.1645	0.4379	0.1835	0.1201	0.4022	0.5837	0.4916	0.8159	0.3600
Musculoskeletal system	0.2678	0.1651	0.1124	0.1828	-0.0324	0.4042	0.3622	0.4958	0.7775	0.3625
Infectious and parasitic diseases	-0.0428	0.2101	-0.2066	0.2144	-0.0893	0.5092	-0.2814	0.6670	1.2552	0.4679
HIV/AIDS	0.7021	0.1709	0.3011	0.1928	0.2587	0.4174	0.6846	0.5087	1.2490	0.3665
Neoplasms	2.1910	0.1715	1.2690	0.2084	1.0409	0.4457	1.0694	0.5131	1.7512	0.3608
Endocrine/nutritional	0.2256	0.1681	0.0556	0.1854	0.1694	0.4134	0.4325	0.5021	0.9175	0.3694
Blood/blood-forming diseases	0.8994	0.2161	0.0504	0.2429	0.2083	0.5335	0.8622	0.6451	1.4116	0.4180
Severe visual impairment	-0.5939	0.1738	-0.3360	0.1903	-1.1611	0.4142	-1.5715	0.5050	0.2785	0.3914
Severe hearing impairment	0.5063	0.1724	0.2675	0.1913	0.2821	0.4217	0.9691	0.5104	1.3214	0.3762
Severe speech impairment	0.4080	0.3326	0.0326	0.3619	-0.4247	0.7968	0.7777	0.9256	1.4060	0.6162
Nervous system	-0.1657	0.1648	-0.2160	0.1814	-0.4424	0.4024	0.6424	0.4968	0.7682	0.3644
Circulatory system	0.2228	0.1666	0.0184	0.1840	-0.0646	0.4068	0.3992	0.5012	0.7571	0.3647
Respiratory system	0.1207	0.1812	-0.0010	0.1955	0.1229	0.4430	0.3743	0.5513	0.6954	0.4006
Digestive system	1.0446	0.1847	0.3876	0.2111	0.5358	0.4930	0.4946	0.5418	1.1272	0.3798
Genitourinary system	1.0117	0.1726	0.4386	0.1954	0.4908	0.4244	0.8377	0.5137	1.4699	0.3674
Skin/subcutaneous tissue	0.2432	0.2585	0.4297	0.2881	-1.2516	0.5683	0.7864	0.8675	0.8251	0.5712
Congenital anomalies	-1.0403	0.2046	-0.5957	0.2016	-0.0883	0.5567	-0.5132	0.7535	0.7373	0.5833
Injuries	0.9527	0.1658	0.4606	0.1860	0.1261	0.4068	0.8561	0.4957	1.2820	0.3601
Other	0.2586	0.1609	0.1206	0.1789	0.4380	0.3922	0.6017	0.4805	0.8940	0.3554
TWP completion month
January	1.4062	0.0431	-0.0337	0.0416	0.7770	0.1162	1.7724	0.1412	3.3805	0.0967
February	1.2590	0.0414	-0.0947	0.0404	0.5190	0.1141	1.4563	0.1363	2.9446	0.0928
March	1.0814	0.0404	-0.0744	0.0408	0.4156	0.1079	1.2204	0.1310	2.4209	0.0917
April	0.9308	0.0391	-0.1504	0.0398	0.2126	0.1037	0.7597	0.1258	2.0860	0.0881
May	0.7810	0.0373	-0.1259	0.0385	0.2464	0.1020	0.6184	0.1206	1.6622	0.0857
June	0.6036	0.0373	-0.1682	0.0390	0.1070	0.1000	0.4729	0.1172	1.1782	0.0864
July	0.3755	0.0383	-0.2203	0.0396	-0.1627	0.1004	0.2120	0.1214	0.8284	0.0896
August	0.1721	0.0384	-0.2256	0.0398	-0.1847	0.1033	0.0275	0.1220	0.4442	0.0924
September	-0.3132	0.0318	-0.2671	0.0329	-0.4202	0.0913	-0.4679	0.1093	-0.0346	0.0860
October	-0.0865	0.0373	-0.2100	0.0386	-0.2496	0.1030	-0.3229	0.1222	-0.0236	0.0942
November	-0.0132	0.0370	-0.1147	0.0389	-0.0920	0.1042	-0.1786	0.1214	0.1028	0.0940
Intercept	1.2935	0.1711	1.1024	0.1890	2.3566	0.4207	2.0928	0.5148	1.1272	0.3809
Number of observations	233,930		121,492		28,678		25,632		58,128
Adjusted R-squared	0.146		0.0868		0.1282		0.1794		0.2765
SOURCE: SSA's 2007 TRF data merged with MEF data.
NOTE: Omitted categories from the regression model include missing race, missing primary disabling condition, missing education status, and TWP completion month in December.

Table A-4. AWI-adjusted DD estimates for the impact of the 1999 SGA earnings-level increase on average monthly earnings from the TWP completion year to the second post-TWP year for the 1996 and 1998 completer cohorts
Average monthly earnings ($)	Percentage of cohort with earnings in category				DD estimate of the effect of the SGA earnings-level increase
	Year of TWP completion		Second post-TWP year		Point estimate	t-statistic	95 percent confidence interval
	1996	1998	1996	1998	Point estimate	t-statistic	95 percent confidence interval
0–199	15.19	15.47	36.00	35.64	-0.63	-1.79	-0.75	0.06
200–499	30.87	31.98	20.96	20.27	-1.81	-5.00	0.35	-1.10
500–699	14.71	13.14	8.82	9.30	2.05	7.75	-3.00	2.57
700–999	11.66	11.24	6.95	7.06	0.52	2.15	-1.44	1.00
1,000 or more	27.57	28.16	27.27	27.74	-0.12	-0.32	-1.33	0.62
SOURCE: SSA's 2007 TRF data merged with MEF data.
NOTES: DD estimates are regression-adjusted to control for differences in the 1996 and 1998 cohorts. Earnings adjusted for wage growth to year-2000 dollars using the contemporaneous AWI.

Table A-5. AWI-adjusted DD estimates for the impact of the 1999 SGA earnings-level increase on mean monthly earnings from the TWP completion year to the second post-TWP year, by earnings interval in the TWP completion year, for the 1996 and 1998 TWP completer cohorts
Average monthly earnings in the TWP year ($)	Percentage of cohort in category		Change in mean monthly earnings of cohort ($)		DD estimate of the impact of the SGA earnings-level increase
Average monthly earnings in the TWP year ($)	1996	1998	1996	1998	Estimate	t-statistic	95 percent confidence interval		Percentage estimate
Total	100.0	100.0	-47.28	-46.12	1.17	0.10	-21.82	24.16	0.1
Weighted total	100.0	100.0	-47.29	-46.12	1.11	0.11	-18.72	20.94	0.1
Less than 500	46.06	47.45	88.23	86.14	-2.08	-0.36	-13.43	9.27	-0.6
500–699	14.71	13.14	-19.33	-11.93	7.39	0.73	-12.50	27.28	1.3
700–999	11.66	11.24	-51.54	-36.02	15.52	0.97	-15.92	46.96	2.0
1,000 or more	27.57	28.16	-286.80	-288.97	-2.17	-0.06	-73.24	68.90	-0.1
SOURCE: SSA's 2007 TRF data merged with MEF data.
NOTES: The change in monthly earnings is calculated from the TWP completion year to 2 years later. DD estimates are regression-adjusted to control for differences in the 1996 and 1998 cohorts. Within each group, the percentage estimate is the DD estimate divided by the mean earnings in the second post-TWP year (2000) of the 1998 TWP completers, net of the DD estimate for the group. Earnings adjusted for wage growth to year-2000 dollars using the contemporaneous AWI.

Table A-6. AWI-adjusted DD estimates for the impact of the 1999 SGA earnings-level increase on the number of NSTW months from the TWP completion year to the second post-TWP year, by earnings interval in the TWP completion year, for the 1996 and 1998 TWP completer cohorts
Average monthly earnings in the TWP year ($)	Percentage of cohort in category		Change in the mean number of NSTW months of cohort		DD estimate of the impact of the SGA earnings-level increase
Average monthly earnings in the TWP year ($)	1996	1998	1996	1998	Estimate	t-statistic	95 percent confidence interval		Percentage estimate
Total	100.0	100.0	2.62	2.49	-0.13	-4.14	-0.19	-0.07	-3.5
Weighted total	100.0	100.0	2.62	2.49	-0.13	-8.42	-0.16	-0.10	-3.4
Less than 500	46.06	47.45	1.49	1.27	-0.22	-6.79	-0.28	-0.16	-12.8
500–699	14.71	13.14	2.39	1.99	-0.41	-5.53	-0.56	-0.26	-13.1
700–999	11.66	11.24	3.15	3.20	0.05	0.46	-0.16	0.26	1.0
1,000 or more	27.57	28.16	4.41	4.50	0.09	1.39	-0.04	0.22	1.3
SOURCE: SSA's 2007 TRF data merged with MEF data.
NOTES: The change in the NSTW months is calculated from the TWP completion year to 2 years later. DD estimates are regression-adjusted to control for differences in the 1996 and 1998 cohorts. Within each group, the percentage estimate is the DD estimate divided by the mean number of NSTW months in the second post-TWP year (2000) of the 1998 TWP completers, net of the DD estimate for the group. Earnings adjusted for wage growth to year-2000 dollars using the contemporaneous AWI.