Using the Core Wave Files

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

Structure of the Core Wave Files

Beginning with the 1990 Panel, the core wave files have been issued in person-month format, with one record per person for each month of the 4-month reference period the person is in the sample.⁵ A person who was in the sample for all 4 months of the wave has four records. A person who was in the sample for 1 month has only one record. Records for persons interviewed by proxy are included in the files, as are records for persons for whom the data are imputed. The files also contain records for all children residing with original panel members.

As Table 10-1 illustrates, person number 0101 (101) was in the sample all 4 months, person number 0102 (102) was also in the sample all 4 months, person number 0201 (201) was in the sample for 2 months, and person number 0202 (202) was in the sample for 1 month. Users may find it helpful to review Figure 2-1 (pp. 2-10-2-14 of the SIPP Users' Guide), which illustrates movement into and out of the sample.

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Identifying Persons

There are many occasions when a user may need to identify which records belong to which individual in the SIPP data files. This need arises, for example, when:

Merging data from topical module or full panel files to core wave files;
Combining data from two or more core wave files;
Linking husbands and wives;
Linking parents and children; and
Identifying which person received government transfer income on behalf of the family.

To uniquely identify a person in the core wave files, analysts should employ the three variables shown in Table 10-2. Users should note that in the 1996 Panel, the entry address ID is no longer needed for unique identification. Its continued use will not create any problems; it is simply redundant information. That is a change from earlier panels in which the entry address ID was key to uniquely identifying persons.

Table 10-1. Person-Month File Structure for the Core Wave Files

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1996 Panel Sample Unit ID (SSUID)	Current Address ID (SHHADID)	Person Number (EPPPNUM)	Rotation Group (SROTATION)	Reference Month (SREFMON)	Calendar Month (RHCALMN)
123451000123	011	0101	2	1	2
123451000123	011	0101	2	2	3
123451000123	011	0101	2	3	4
123451000123	011	0101	2	4	5
123451000123	011	0102	2	1	2
123451000123	011	0102	2	2	3
123451000123	011	0102	2	3	4
123451000123	011	0102	2	4	5
123451000123	021	0201	2	1	2
123451000123	021	0201	2	2	3
123451000123	022	0202	2	4	5
Prior to the 1996 Panel
Sample Unit ID (SUID)	Current Address ID (ADDID)	Person Number (PNUM)	Rotation Group (ROT)	Reference Month (REFMTH)	Calendar Month (MONTH)
123451000	11	101	2	1	2
123451000	11	101	2	2	3
123451000	11	101	2	3	4
123451000	11	101	2	4	5
123451000	11	102	2	1	2
123451000	11	102	2	2	3
123451000	11	102	2	3	4
123451000	11	102	2	4	5
123451000	21	201	2	1	2
123451000	21	201	2	2	3
123451000	22	202	2	4	5

Table 10-2. Variables Used to Uniquely Identify a Person in the Core Wave Files

Variable Name	Description
SSUID (SUID)	Sample unit ID
EENTAID (ENTRY)	Entry address ID (Not required for identification in the 1996 Panel)
EPPPNUM (PNUM)	Person number

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The variables in Table 10-2 have the following characteristics:

SSUID (SUID) uniquely identifies each initially sampled dwelling unit.⁶ Every person in a core wave file was either a member of one of those units (an original sample member) or lives with someone who was a member of an initially sampled dwelling unit. A person’s connection to that unit is an attribute of that person and does not change over time.⁷ This means that as people move from address to address, their SSUID (SUID) stays the same. As new people join the homes of original sample members, they receive the SSUID (SUID) of the original sample members.
EENTAID (ENTRY) identifies the address where the person lived at the time she or he was first interviewed. It does not change even if the person moves.⁸ Prior to the 1996 Panel, it was used in conjunction with the person number and sample unit ID to uniquely identify persons within the sampling unit. It is not needed to uniquely identify persons in the 1996 panel. Values for this variable are unique only within sample units. The entry address ID has two components. The first part of the ID number (two digits in the 1992 and 1996 Panels, and one digit in all others) identifies the wave in which SIPP interviews were first conducted at the address. The second part of the number (one digit in all panels) sequentially numbers addresses within a sample unit [SSUID (SUID)] that enter the sample in the same wave. See Chapter 9 for a more complete discussion.
Prior to the 1996 Panel, PNUM uniquely identified a person within the sample unit and entry address ID. In the 1996 Panel, EPPPNUM uniquely identifies a person within the sample unit. EPPPNUM (PNUM) does not change even if the person moves.⁹ The first part of EPPPNUM (PNUM) (two digits in the 1992 and 1996 Panels, one digit in all others) indicates the wave in which the person was first interviewed.¹⁰ The remaining two digits are sequentially assigned within the household. Thus, original sample members are assigned person numbers ranging from 100 to 199. Individuals who enter the SIPP sample in Wave 2 are assigned a person number ranging from 200 to 299. Those who enter in Wave 10 are assigned person numbers ranging from 1001 to 1099.

Table 10-3 in the illustrates how the combination of SSUID (SUID), EENTAID (ENTRY), and EPPPNUM (PNUM) uniquely identifies people and provides information about when they first entered the SIPP sample. In this example, there are eight individuals: five are original sample members, one person joined the SIPP sample in Wave 3, one joined in Wave 4, and another joined in Wave 7. Note that the person who joined the sample in Wave 3 (pre-1996 Panel) was assigned a person number of 301, but an entry address ID of 21 (not 31). That is because the first part of the entry address ID indicates the wave in which that address was first occupied by any SIPP sample member, which is not necessarily the wave in which a given member entered the sample.

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Table 10-3. How to Uniquely Identify a Person in the Core Wave Files

1996 Panel
Sample Unit ID (SSUID)	Entry Address ID (EENTAID)	Person Number (EPPPNUM)	Notes
123456789123	011	0101	Original sample member
123456789123	011	0102	Original sample member
123456789123	022	0301	Enters SIPP sample in Wave 3
123456789123	011	0401	Enters SIPP sample in Wave 4
123456789123	071	0701	Enters SIPP sample in Wave 7
321456789123	011	0101	Original sample member
321456789123	011	0102	Original sample member
321456789123	011	0103	Original sample member
Prior to the 1996 Panel
Sample Unit ID (SUID)	Entry Address ID (ENTRY)	Person Number (PNUM)	Notes
123456789	11	101	Original sample member
123456789	11	102	Original sample member
123456789	21	301	Enters SIPP sample in Wave 3
123456789	11	401	Enters SIPP sample in Wave 4
123456789	71	701	Enters SIPP sample in Wave 7
321456789	11	101	Original sample member
321456789	11	102	Original sample member
321456789	11	103	Original sample member

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__________
⁵ Prior to the 1990 Panel, core wave files had one record per person. Each record contained four occurrences of each monthly variable. For more information, see earlier editions of the SIPP Users’ Guide.
⁶ The SSUID (SUID) is a random recode of three other variables in the Census Bureau’s internal (not public use) files: the respondent’s sampling area (PSU), the cluster of housing units within that area (called the "segment"), and a sequentially assigned serial number. Those variables are omitted from the public use files to protect the confidentiality of the respondents.
⁷ There is one rare exception to this rule for Panels prior to 1996, which is described in the section entitled "Identifying Movers" later in this chapter.
⁸ See footnote 6.
⁹ See footnote 6.
¹⁰ For Wave 10 of the 1992 Panel and for the 1996 Panel, the first two digits of PNUM instead of the first digit identify the wave in which the person entered sample.

SIPP Public Use Files

Using the Core Wave Files

Using Topical Module Files

Using the Full Panel Longitudinal Research Files

Linking Core Wave, Topical Module and Full Panel Files

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Page Last Modified: May 9, 2006

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