# Presentation: 538760

## NCHS Research Data Center

- Vijay  Gambhir
- Computer Scientist
- (301) 458-4226
- Vgambhir@cdc.gov

- Kenneth W. Harris
- Acting Director
- (301) 458-4262
- Kwh1@cdc.gov

**CDC/NCHS****Research Data Center**
- Presented July 23, 2003
- Bureau of Transportation Statistics
- Confidentiality Seminar Series

**Notes:**
Ken 1

## Operational Comparison of the NCHS Research Data Center and the Census Research Data Center

|  | NCHS RDC | Census RDC |
| --- | --- | --- |
| Data available | Virtually any NCHS survey without direct identifiers | Title 13 data such as CPS, MEPS, and others |
| Researcher-supplied data | Allowed | Allowed |
| Research proposals | Required | Required |
|             Review cycle | Continuous | Three times per year |
|             Turn-around time | 2-3 weeks | 4-8 months |
| Tenure at RDC | Short term or long term (minimum charge of 2 days) | Minimum 3 months |
| Remote Access | Yes | No |

**Notes:**
ken2

|  | NCHS RDC | Census RDC |
| --- | --- | --- |
| Type of projects | Tabular or model-based | Model-based only |
| Researcher costs |  |  |
|        Remote access | $500/month if file size < 130,000 records.
$1000/month if file size > 130,000 records.
 | N/A |
|       On site | $200/day |  |

## Operational Comparison of the NCHS Research Data Center and the Census Research Data Center

| File set up | $500/day’s effort | N/A |
| --- | --- | --- |
| Computer equipment |  |  |
| Hardware | Windows NT server/Windows 2000 workstations | Unix server
As described in Reznek talk |
| Software | SAS/Fortran/Stata
Others available upon request | SAS/Stata
Others available upon request |

**Note: At this time files containing restricted or confidential data cannot be transmitted across data center boundaries.**

## Analytic Data Research by Email (ANDRE)

- NCHS has been providing remote data access to the researchers through ANDRE since April 1998
- In the past five years ANDRE has served 45 different data analysts and executed over 10,000 SAS programs for their research programs.

## Main Features of ANDRE

- Completely automated system. Operates round the clock without any human intervention
- Registered subscribers only.
- Proposals already reviewed and approved
- Have an agreement with NCHS/RDC
- Unlimited access during the subscription period

## Data Requests

- Registered user can submit data requests by email from anywhere and at any time.
- Results of the data request released to a specified email address that has been certified to be secure by the subscriber and approved by NCHS/RDC

## Authentication

- Multi-levels of system security:
- Submission syntax
- User id
- Password
- Email/code word
- Package
- Path info

## Data Request Analysis

- Compliance with the disclosure limitation constraints of NCHS
- Integrity of the system
- Resource constraints (CPU time & Storage requirements)
- Protection of ANDRE’s work environment

**Notes:**
Disclosure limitation: Forbidden words

## Prevention of Direct Disclosure

- Cleaning up of the Log File
- Categorization of SAS commands/words
- Forbidden Commands
- Modifications to the Commands
- Output suppression

## Sample:-  Original Log

- 1    options nocenter;
- 2    Data one;
- 3    Infile 'd:\nchs\respnd95.dat' lrecl=13064;
- 4    Input
- 5    TODAYSPG 6847-6847
- 6    CONSTAT1 11934-11935
- 7    CONSTAT2 11936-11937
- 8    CONSTAT3 11938-11939
- 9    CONSTAT4 11940-11941
- 10   SEX1MTHD 11945-11946
- 11   POST_WT  12350-12359;
- 12   if constat1 = 'ab' then vjvar=1; else vjvar = 2;
- 13   WGT1000=POST_WT/1000;
- 14   title 'NSFG cycle 1995';
- NOTE: Character values have been converted to numeric values at the places given by: (Line):(Column).
-       12:15
- NOTE: The infile 'd:\nchs\respnd95.dat' is:
-       File Name=d:\nchs\respnd95.dat,
-       RECFM=V,LRECL=13064
**NOTE: Invalid numeric data, 'ab' , at line 12 column 15.                                                                     **
**RULE:     ----+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8----+----9----+----0               **
**1         1000000111260837511521 1                                    1050  12         106921124112411189                    **
**     ****101                                                                              2                                      **
**     ****201        19211059110611197**
**	****	****	****......****	**
**	****	****	****......**
**	****	****	****......**

## Sample:-  Original Log (cont.)

**	****	****	****......****	**
**	****	****	****......**
** ****12901       11232521101 05267213103033921811931011103  01030000000321120000392702210611511200403 1344  1316               **
**   ****13001  622501001006034                                                                                                    **
**TODAYSPG=1 CONSTAT1=5 CONSTAT2=88 CONSTAT3=88 CONSTAT4=88 SEX1MTHD=1 POST_WT=2545.7569 vjvar=2 WGT1000=2.5457569 _ERROR_=1   **
**_N_=20**
- NOTE: 10847 records were read from the infile 'd:\nchs\respnd95.dat'.
-       The minimum record length was 13064.
-       The maximum record length was 13064.
- NOTE: The data set WORK.ONE has 10847 observations and 9 variables.
- NOTE: DATA statement used:
-       real time           39.88 seconds
-       cpu time            12.10 seconds
- 15   proc freq;
- 16   tables CONSTAT1 vjvar;
- 17   run;
- NOTE: There were 10847 observations read from the data set WORK.ONE.
- NOTE: PROCEDURE FREQ used:
-       real time           0.49 seconds
-       cpu time            0.04 seconds

## Sample:- Cleaned Log

- 1    options nocenter;
- 2    Data one;
- 3    Infile 'd:\nchs\respnd95.dat' lrecl=13064;
- 4    Input
- 5    TODAYSPG 6847-6847
- 6    CONSTAT1 11934-11935
- 7    CONSTAT2 11936-11937
- 8    CONSTAT3 11938-11939
- 9    CONSTAT4 11940-11941
- 10   SEX1MTHD 11945-11946
- 11   POST_WT  12350-12359;
- 12   if constat1 = 'ab' then vjvar=1; else vjvar = 2;
- 13   WGT1000=POST_WT/1000;
- 14   title 'NSFG cycle 1995';
- NOTE: Character values have been converted to numeric values at the places given by: (Line):(Column).
-       12:15
- NOTE: The infile 'd:\nchs\respnd95.dat' is:
-       File Name=d:\nchs\respnd95.dat,
-       RECFM=V,LRECL=13064
**NOTE: Invalid numeric data, 'ab' , at line 12 column 15.                                                                     **

## Sample:- Cleaned Log (cont.)

**NOTE: 10847 records were read from the infile 'd:\nchs\respnd95.dat'.                                                        **
**      ****The minimum record length was 13064.                                                                                   **
-       The maximum record length was 13064.
- NOTE: The data set WORK.ONE has 10847 observations and 9 variables.
- NOTE: DATA statement used:
-       real time           39.88 seconds
-       cpu time            12.10 seconds
- 15   proc freq;
- 16   tables CONSTAT1 vjvar;
- 17   run;
- NOTE: There were 10847 observations read from the data set WORK.ONE.
- NOTE: PROCEDURE FREQ used:
-       real time           0.49 seconds
-       cpu time            0.04 seconds

## Forbidden Commands

- Commands that pose unacceptable disclosure risks					OR
- Disallowed to protect integrity/internal environment of ANDRE
- Add		editor 	 report		 iml
- Print		 first.		 Pctn			nofreq
- Obs		 last.		 Pctsum		 nocum
- Firstobs	 nocol	 tabulate		 editor
- Browse	 summary	 list			 put

## Commands Modification

- Modify user’s program to enforce  restrictions on options allowed with certain SAS procedures to prevent objectionable info appearing in the output
- 	***PROC MEANS  n mean std****;*

## Output Suppression

- Wiping out of extreme values from the output of Proc Univariate
- Suppressing complete output line (Procs Means, corr, Univariate etc) where sample size less than the minimum acceptable value.

## Proc Means Suppression

- The MEANS Procedure
- Variable    Label                                          N            Mean         Std Dev
- --------------------------------------------------------------------------------------------
- EXPEND_R    Current expend/pupil in public schl/1000    5424       5.0830820       1.3958710
-                                          ***** Values Suppressed *****
- RPUB87      exp. for contr. serv. and supplies 1997$    5424     23472052.60     18806802.86
- RPUB92      exp. for contr. serv. and supplies 1997$    5424     34800922.98     30481634.59
- PRGPRO      Coordinated Pregnancy Prevention Program    1708       0.0679157       0.2516749
- HIVED       HIV/AIDS Education                          1708       3.5146370       0.8044378
-                                          ***** Values Suppressed *****
- PRGPRO87    Coordinated Pregnancy Prevention Program    5424       0.0540192       0.2260764
- HIVED87     HIV/AIDS Education                          5424       3.4968658       0.8008324
- WT_PER15    % Wt females aged 15-19/total 15-19         5424       0.7279681       0.1265796
- BK_PER15    % Bk females aged 15-19/total 15-19         5424       0.1409869       0.0932332
- HS_PER15    % Hs females aged 15-19/total 15-19         5424       0.0962413       0.1055191
- TEENMMC2    Teenmom by cohort (1,2,3r)                  1201       1.7119067       0.7715351
- C18_2_1S    R in C2 (vs 1) at 18-19 endpt (1,2)         1770       1.5248588       0.4995228
- TM2_1S18    R tnmm in Coh 2 (vs 1)-age 18 @ ext          358       1.4804469       0.5003168
- AGE_12      Date R = 12 in century months               6450     979.5613953      69.3124265
- STRTST      IA5 Date R started living in current sta    3870         1132.55     753.2066507
- BDAYCENM    R date of birth                             6450     835.5613953      69.3124265
- RAVPAY95    real av. an. pay 95 dollars                 5424        26933.93         2826.80
- PERCAFDC    percent of households receiving AFDC        5424       0.0422254       0.0127307
- SALARY      teacher salaries real 96-97$$$              5424        35338.66         5729.11
- --------------------------------------------------------------------------------------------

## Proc Univariate OutputUnsuppressed

-   The SAS System                                   9
-                                                        14:09 Sunday, October 24, 1999
-                                 Univariate Procedure
- Variable=AVHRATET
-                  Moments                                 Quantiles(Def=5)
-  N              2283  Sum Wgts       2283     100% Max  -0.25314       99%  -1.62008
-  Mean       -4.66219  Sum        -10643.8      75% Q3   -3.56179       95%  -2.37588
-  Std Dev    1.892017  Variance    3.57973      50% Med  -4.50491       90%  -2.79152
-  Skewness   -2.11919  Kurtosis   6.892929      25% Q1   -5.30374       10%  -6.07639
-  USS        57792.36  CSS        8168.944       0% Min  -13.5463        5%  -7.19645
-  CV         -40.5821  Std Mean   0.039598                               1%  -12.7402
-  T:Mean=0   -117.738  Pr>|T|       0.0001     Range     13.29321
-  Num ^= 0       2283  Num > 0           0     Q3-Q1     1.741949
-  M(Sign)     -1141.5  Pr>=|M|      0.0001     Mode      -13.5463
-  Sgn Rank   -1303593  Pr>=|S|      0.0001
**                                      ****Extremes**
-                          **Lowest    Obs     Highest    Obs                             **
**                       ****-13.5463(    1547) -0.90519(     649)                          **
**                       ****-13.5397(    1836) -0.81756(    1094)                          **
**                       ****-13.4637(    2084) -0.76928(    1739)                          **
**                       ****-13.4413(    1127)  -0.5907(      21)                          **
**                       ****-13.4402(    1088) -0.25314(     400)                          **

## Proc Univariate OutputSuppressed

- The SAS System                                   9
-                                                        14:09 Sunday, October 24, 1999
-                                 Univariate Procedure
- Variable=AVHRATET
-                  Moments                                 Quantiles(Def=5)
-  N              2283  Sum Wgts       2283     100% Max  -0.25314       99%  -1.62008
-  Mean       -4.66219  Sum        -10643.8      75% Q3   -3.56179       95%  -2.37588
-  Std Dev    1.892017  Variance    3.57973      50% Med  -4.50491       90%  -2.79152
-  Skewness   -2.11919  Kurtosis   6.892929      25% Q1   -5.30374       10%  -6.07639
-  USS        57792.36  CSS        8168.944       0% Min  -13.5463        5%  -7.19645
-  CV         -40.5821  Std Mean   0.039598                               1%  -12.7402
-  T:Mean=0   -117.738  Pr>|T|       0.0001     Range     13.29321
-  Num ^= 0       2283  Num > 0           0     Q3-Q1     1.741949
-  M(Sign)     -1141.5  Pr>=|M|      0.0001     Mode      -13.5463
-  Sgn Rank   -1303593  Pr>=|S|      0.0001

## Proc Univariate OutputSuppressed (sample size = 1)

-                                 **Univariate Procedure                                  **
**Variable=FREQ          (sum) freq                                                     **
**                 ****Moments                                 Quantiles(Def=5) **
**            **
** ****	****	****	****Serious Disclosure limitation Violations**
**	****	****	****Values too low to release**
**	****	****	****Output of Proc Univariate withheld**

## Proc Freq Suppression (one way Tables)

- Suppress at least two consecutive rows to prevent derivation of suppressed values from cumulative totals.
- Disallow single row output.

## 1-Way Freq Tablesuppressed

- 			Cumulative  	    Cumulative
-   LOGRNTOPAT    Frequency     Percent     Frequency      Percent
- -----------------------------------------------------------------
**0.2277839309       ?????       ?????         ?????        ?????**
**0.2277839309       ?????       ?????         ?????        ?????**
- 0.2305236586           5        0.08          6429        97.99
-  0.231111721           5        0.08          6434        98.06
-  **0.232058915       ?????       ?????         ?????        ?????**
** ****0.232058915       ?????       ?????         ?????        ?????**
**0.2436220827       ?????       ?????         ?????        ?????**
**0.2436220827       ?????       ?????         ?????        ?????**
- 0.2498117984           6        0.09          6456        98.40
- 0.2504106777           6        0.09          6462        98.49
- 0.2513144283          18        0.27          6480        98.77
- 0.2595111955           6        0.09          6486        98.86
**0.2670627852       ?????       ?????         ?????        ?????**
**0.2670627852       ?????       ?????         ?????        ?????**
- 0.2736958305           5        0.08          6500        99.07
- 0.2814124594           5        0.08          6505        99.15
- 0.3022808719           6        0.09          6511        99.24
- 0.3364722366          10        0.15          6521        99.39

## 1-Way Freq Tablesuppressed (cont.)

- 			Cumulative  	    Cumulative
-   LOGRNTOPAT    Frequency     Percent     Frequency      Percent
- -----------------------------------------------------------------
**0.3403258059       ?????       ?????         ?????        ?????**
**0.3403258059       ?????       ?????         ?????        ?????**
- 0.3715635564           6        0.09          6537        99.63
**0.3856624808       ?????       ?????         ?????        ?????**
**0.3856624808       ?????       ?????         ?????        ?????**
- 0.6931471806           6        0.09          6550        99.83
**1.2527629685       ?????       ?????         ?????        ?????**
**1.2527629685       ?????       ?????         ?????        ?????**
**1.2527629685       ?????       ?????         ?????        ?????**

## Proc Freq Suppression (Two way Tables)

- Rows and columns totals preserved
- Cells with values less than the acceptable minimum are suppressed
- Additional suppressions to ensure that no row and no column has single suppression.
- Logical stitching of horizontal and vertical splits.

## Proc Freq:  2-way Tables Suppression

-  TABLE OF FAMREL BY FAMSIZER
-                 FAMREL     FAMSIZER
-                 Frequency|
-                 Percent  |
-                 Row Pct  |
-                 **Col Pct  |       2|       3|       4|       5|  Total                 **
**                ****---------+--------+--------+--------+--------+                        **
**                ****3        |     94 |    388 |    792 |    533 |   2206                 **
**                         ****|   3.97 |  16.40 |  33.47 |  22.53 |  93.24                 **
**                         ****|   4.26 |  17.59 |  35.90 |  24.16 |                        **
**                         ****|  98.95 |  96.28 |  96.12 |  94.34 |                        **
**                ****---------+--------+--------+--------+--------+                        **
**                ****4        | ?????? |      9 |     22 |     27 |    104                 **
**                         ****| ?????? |   0.38 |   0.93 |   1.14 |   4.40                 **
**                         ****| ?????? |   8.65 |  21.15 |  25.96 |                        **
**                         ****| ?????? |   2.23 |   2.67 |   4.78 |                        **
**                ****---------+--------+--------+--------+--------+                        **
**                ****6        | ?????? |      6 |     10 |      5 |     56                 **
**                         ****| ?????? |   0.25 |   0.42 |   0.21 |   2.37                 **
**                         ****| ?????? |  10.71 |  17.86 |   8.93 |                        **
**                         ****| ?????? |   1.49 |   1.21 |   0.88 |                        **
**                ****---------+--------+--------+--------+--------+                        **
**                ****Total          95      403      824      565     2366                 **
**                             ****4.02    17.03    34.83    23.88   100.00                 **
**                ****(Continued)                                                           **

## Proc Freq:  2-way Tables Suppression (Cont.)

-  checking frequencies                                4
-                                                           12:01 Thursday, May 6, 1999
-                              TABLE OF FAMREL BY FAMSIZER
-                 FAMREL     FAMSIZER
-                 Frequency|
-                 Percent  |
-                 Row Pct  |
-                 Col Pct  |       6|       7|       8|       9|  Total
-                 ---------+--------+--------+--------+--------+
-    	                **3         |    209 |     98 |     19 |     73 |   2206                 **
**                         ****|   8.83 |   4.14 |   0.80 |   3.09 |  93.24                 **
**                         ****|   9.47 |   4.44 |   0.86 |   3.31 |                        **
**                         ****|  90.48 |  83.05 |  59.38 |  74.49 |                        **
**                ****---------+--------+--------+--------+--------+                        **
**                ****4        |     13 |     10 | ?????? |     12 |    104                 **
**                         ****|   0.55 |   0.42 | ?????? |   0.51 |   4.40                 **
**                         ****|  12.50 |   9.62 | ?????? |  11.54 |                        **
**                         ****|   5.63 |   8.47 | ?????? |  12.24 |                        **
**                ****---------+--------+--------+--------+--------+                        **
**                ****6        |      9 |     10 | ?????? |     13 |     56                 **
**                         ****|   0.38 |   0.42 | ?????? |   0.55 |   2.37                 **
**                         ****|  16.07 |  17.86 | ?????? |  23.21 |                        **
**                         ****|   3.90 |   8.47 | ?????? |  13.27 |                        **
**                ****---------+--------+--------+--------+--------+                        **
**                ****Total         231      118       32       98     2366                 **
**                             ****9.76     4.99     1.35     4.14   100.00                 **

## Contact Information

- For general Questions/Comments
- Email :  _[rdca@cdc.gov](mailto:rdca@cdc.gov)__  __	__ _Phone: (301) 458-4732
- For On-site Info:
- Email :  _[Neb9@cdc.gov](mailto:Neb9@cdc.gov)__  __	__ _Phone: (301) 458-4097
- For Remote Access Info:
- Email :  _[vgambhir@cdc.gov](mailto:vgambhir@cdc.gov)__   _Phone: (301) 458-4226