SIPP Public Use Files

When text copy applies to both 1996 and pre-1996 panel files, pre-1996 variable names appear in parentheses following 1996 variable names.

Section I of the SIPP Users' Guide is written primarily for researchers who need information to guide their use of data from the Survey of Income and Program Participation (SIPP). It describes the design and content of SIPP and the processing of SIPP data by the Census Bureau. It also discusses weighting, sampling error, and nonsampling error.

Section II of the SIPP Users' Guide addresses the mechanics of using the SIPP public use files. The chapters in this section are written for the analyst needing guidance on how to accomplish a variety of common tasks. This section contains minimal discussion of underlying concepts (such as the relationship between waves, rotation groups, and reference months), which are examined in Section I of the SIPP Users' Guide.

There are five chapters in Section II of the SIPP Users' Guide: Chapter 9 provides a general introduction to the public use files; one chapter is devoted to each of the three types of SIPP data files, and a final chapter discusses merging multiple SIPP data files. After reading the current chapter, the user working with just one type of SIPP data file may wish to turn to the chapter on that type of file. For the 1996 Panel, most variable names changed from those of previous panels. To aid users working with files from panels prior to 1996, the chapters in Section II present both the pre- and post- 1996 Panel variable names when the text applies to both 1996 and pre-1996 panel files (when the 1996 Panel names are available). In the main body of the text, the pre-1996 Panel names are presented in parentheses following those from the 1996 Panel. For example, the sample unit ID variable name in the core wave files, which is "SSUID" in the 1996 Panel, was SUID in previous panels. The variable name is written in Chapter 9 of the SIPP Users' Guide as SSUID (SUID). In tables, a variety of methods are used to present both sets of names.

The balance of this chapter provides an overview of the chapters that follow. Those chapters offer more detailed discussions, complete with specific examples and samples of programming code. This introduction highlights points that are common to all SIPP data files. It also highlights important differences.

Types of SIPP Data Files

There are three types of public use files containing SIPP data: core wave files, topical module files, and full panel longitudinal research files (referred to as either longitudinal files or full panel files):

Core wave files are currently issued in person-month format. These files contain up to four records for each primary sample member and each person who lived with a primary sample member at any time during the 4-month reference period covered by the wave. Each of the records contains data from one of the four reference months covered by the wave.¹
Topical module files for the 1996 Panel contain one record for each person who was a sample responding (or Type Z nonresponding) member of a SIPP household during the fourth month of the reference period for the wave. Topical module files from earlier panels contain one record for each primary sample member and each person who lived with a primary sample member at the time of the interview for the wave in which the topical module was administered.
Full panel longitudinal research files contain one record for each primary sample member and for each person who ever lived with a primary sample member at any time during the SIPP panel—a period of up to 4 years.

Understanding the ID Variables in SIPP

Because different files contain different information, the capacity to identify people across those files is important. SIPP is a longitudinal survey designed to allow researchers to track people over time; other critical functions include identifying individuals over time and identifying when a person is present in the sample. Finally, because the relationships among people change over time, identification of those relationships at any specific time is important. The key to these tasks lies in understanding how SIPP ID variables are used to identify persons, families, and households.¹

The most basic ID variables in SIPP have different variable names in the different types of public use files issued by the Census Bureau. Table 9-1 displays those variables and shows the names they are given in the different files.

Sample Unit IDs

When initial Wave 1 interviews are conducted, each physical dwelling unit is assigned a unique (random) sample unit ID.² The sample unit ID assigned to a person never changes: in all subsequent interviews, the Wave 1 primary sample persons carry their sample unit IDs with them. This means that if they move to different addresses, they keep the same sample unit IDs. If new people join those original sample members at their original addresses, they become secondary sample members by virtue of their association with the primary sample person with whom they are living. Secondary sample persons are all assigned the sample unit ID of the primary sample member with whom they are living. At the conclusion of the panel, all people who have ever lived with a member of a given original sample unit share the same sample unit ID. That sample unit ID is their common link to the original sample unit.

Table 9-1. SIPP Variable Names, by File Type

File Type	Sample Unit ID	Current Address ID	Entry Address ID	Person Number
Panels Prior to the 1996 Panel
Core Wave Person-Month Files	SUID	ADDID	ENTRY	PNUM
Topical Module Files	ID	ADDID	ENTRY	PNUM
Full Panel (and Partial-Panel) Longitudinal Research Files	PP-ID	HH-ADDID	PP-ENTRY	PP-PNUM
1996 Panel
Core Wave Person-Month Files	SSUID	SHHADID	EENTAID (No longer needed to identify persons)	EPPPNUM
Topical Module Files	SSUID	SHHADID	EENTAID (No longer needed to identify persons)	EPPPNUM
Full Panel (and Partial-Panel) Longitudinal Research Files	File not yet available. Current plans call for using the same ID variable names in all files from the 1996 Panel.

Current Address IDs

The current address ID identifies each housing unit occupied by one or more original sample members in any given month.³ Current address IDs are assigned within sample units (they are unique only when combined with the sample unit ID variable), and they have two parts. The first part (one digit for all but the 1992 and 1996 Panels, two digits for the 1992 and 1996 Panels) identifies the wave in which one or more original sample members were first scheduled to be interviewed at the address. The second part of the ID is one digit, and it is used to sequentially number addresses for households that split into two or more households as a result of a move to a different location by original sample persons. All Wave 1 households have a current address ID of 11. Any new addresses that are occupied in Wave 2 are numbered 21, 22, and so on; new addresses occupied during the Wave 3 reference period are numbered 31, 32, 33, and so on. The current address ID is a monthly variable, the value of which changes in the month in which an individual moves to a new address.

Entry Address IDs

The entry address ID is the current address ID that a sample member occupied when he or she first entered the SIPP sample. It is used in conjunction with the person number to uniquely identify persons within the sample unit and does not change even if the person moves.

Person Numbers

All primary and secondary sample members are assigned a person number when they first enter the SIPP panel. Those numbers are assigned sequentially, within each wave and within each household (current address). The first part of the person number (two digits for the 1992 and 1996 Panels, one digit for all others) indicates the wave in which the person originally entered the sample. Thus, primary sample persons have person numbers in the 100 series, beginning with 101; secondary sample members have person numbers beginning with 201 if they enter the sample in Wave 2, 301 if they enter the sample in Wave 3, 401 if they enter the sample in Wave 4, and so on.

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^[1]Other variables are used to identify people who are members of related subfamilies, unrelated subfamilies (also known as secondary families), and transfer program units such as food stamp units.

^[2] The sample unit ID is a random recode of three other variables in the Census Bureau internal files: the respondent’s sampling area, the cluster of housing units within that area (called a segment), and a sequentially assigned serial number. Because the variables in the Census Bureau’s internal files contain detailed information about the location of the dwelling unit, those variables are suppressed in the public use files to protect the confidentiality of survey respondents.

^[3] A house, an apartment or other group of rooms, or a single room is regarded as a housing unit if it is occupied or intended for occupancy as separate living quarters.

SIPP Public Use Files

Using the Core Wave Files

Using Topical Module Files

Using the Full Panel Files

Linking Core Wave, Topical Module and Full Panel Files

Analysis Example
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Page Last Modified: May 9, 2006

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