In-law Classification Procedures for 2000-2007 American Community Survey (ACS) and 2005-2007 Puerto Rican Community Survey (PRCS)

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In the 2000-2007 ACS and the 2005-2007 PRCS questionnaires, the item inquiring about relationships to the household head includes only a single "in-law" category that does not distinguish among parents-in-law, siblings-in-law, and children-in-law. For consistency with other years and greater accuracy in constructing family inter-relationship variables, IPUMS separates this global in-law category into its three separate types.

IPUMS had made these detailed in-law assignments since the release of the earliest ACS sample in 2003. In early 2009, we made several changes to the logic used to make the assignments, and we have applied the newer approach to ALL ACS and PRCS samples.

The new classification scheme uses seven pieces of information:

  • the in-law's age
  • the household head's age
  • the household head's spouse's age
  • the presence in the household of married children of the head
  • the presence in the household of married siblings of the head
  • the in-law's marital status
  • the household head's marital status

Generally speaking, people who are several years younger than the head and/or the head's spouse are classified as children-in-law; people who are relatively close in age to the head and/or the head's spouse are classified as siblings-in-law; and people who are several years older than the head and/or the head's spouse are classified as parents-in-law. These rules are relaxed somewhat when there are married children and/or married siblings of the head in the household, which suggest (respectively) that children-in-law and siblings-in-law are likely to be present. And these rules are overridden by marital status: no never-married person can be a child-in-law; most never-married persons are classified as siblings-in-law; and nobody can be classified as a parent-in-law unless the head of the household has ever been married.

More specifically:

  1. Unless they have never been married, individuals are classified as children-in-law if they meet at least one of the following conditions:
    • are at least 17 years younger than the head when the head's spouse is not present
    • are at least 10 years younger than the head and at least 17 years younger than the head's spouse when the head's spouse is present
    • are at least 6 years younger than the head (and at least 6 years younger than the head's spouse, if present) when there are married children or grandchildren of the head present in the household.
  2. Individuals are classified as siblings-in-law if they were not classified as a child-in-law in the previous step and at least one of the following conditions applies:
    • they have never married
    • the household head has never married
    • they are no more than 16 years younger than the head and no more than 10 years older than the head
    • they are no more than 16 years younger than the head's spouse (if present) and no more than 10 years older than the head's spouse (if present)
    • they are younger than the head's spouse and older than the head when the head's spouse is present
    • there are married siblings present in the household and at least one of the following is true:
      • they are no more than 20 years younger than the head and no more than 17 years older than the head
      • they are no more than 20 years younger than the head's spouse (if present) and no more than 17 years older than the head's spouse (if present)
  3. Individuals are classified as parents-in-law if they were not classified as children-in-law or siblings-in-law in the previous steps and meet at least one of the following conditions:
    • they are at least 11 years older than the head and the head's spouse is not present
    • they are at least 11 years older than the head's spouse
  4. Finally, all siblings-in-law are re-classified as parents-in-law if they are at least 18 years older than the head (where the head's spouse is not present) or are at least 18 years older than the head's spouse (where the head's spouse is not present).
Previous classification scheme

Until early 2009, IPUMS used only the marital status and age variables to make the more detailed in-law assignments. Persons at least 11 years older than the household head were classified as parents-in-law; those at least 17 years younger than the household head were classified as children-in-law; and those no more than 10 years older than the head and no more than 16 years younger than the head were classified as siblings-in-law. Additionally, all never-married persons were classified as siblings-in-law.

This classification scheme was usually accurate, but occasionally yielded implausible household structures. Here are some representative examples from the 2000 5% PUMS, which contains detailed information on in-laws. In all of them, applying the old classification scheme results in errors:

Example and person number Spouse location Age Sex Marital Status Actual Relationship Relationship Under Old Classification Scheme
Example 1  
1 -- 79 F Divorced Head/Householder Head/Householder
2 3 51 F Married Child Child
3 2 71 M Married Child-in-law Sibling-in-law
Example 2  
1 2 57 M Married Head/Householder Head/Householder
2 1 36 F Married Spouse Spouse
3 -- 64 F Divorced Sibling-in-law Sibling-in-law
4 -- 38 M Divorced Sibling-in-law Child-in-law
Example 3  
1 2 57 M Married Head/Householder Head/Householder
2 1 67 F Married Spouse Spouse
3 -- 71 F Widowed Sibling-in-law Parent-in-law
Example 4  
1 -- 27 M Never married Head/Householder Head/Householder
2 -- 26 M Never married Sibling Sibling
3 4 34 F Married Sibling Sibling
4 3 45 M Married Sibling-in-law Parent-in-law
Example 5  
1 2 77 M Married Head/Householder Head/Householder
2 1 68 F Married Spouse Spouse
3 -- 87 F Widowed Parent-in-law Sibling-in-law

In Example 1, the daughter (person 2) of the head (person 1) married a man twenty years older (person 3). The man is therefore a son-in-law of the head despite being only eight years younger than the head. This falls within the age range of a sibling-in-law under the old classification scheme, which fails to recognize that the head's children can marry older spouses, so the son-in-law is misclassified as a brother-in-law.

In Example 2, the head (person 1) married a much younger woman (person 2) who has a brother of a similar age (person 3). Yet because the brother-in-law is nineteen years younger than the head, he is classified instead as a son-in-law. Here the problem is that the old classification scheme is insensitive to the head's spouse's age.

In Example 3, the head (person 1) married an older woman (person 2) who has an older sister (person 3). The head's sister-in-law is fourteen years older than the head, making her a mother-in-law under the old classification scheme. But for this to be the case, the putative mother-in-law would have given birth to the head's spouse at age 4. Again, the head's spouse's age contains vital information not captured in the old classification scheme.

Example 4 is similar to Example 3: a sibling-in-law (person 4) who is 18 years older than the head (person 1) is mistakenly classified as a parent-in-law. However, in this case, the sibling-in-law is the older spouse of the head's older sibling, not the older sibling of the head's older spouse. In fact, the head has never married, so it is logically impossible for him to have a parent-in-law despite the difference in their ages.

Example 5 shows a head (person 1) who married a younger woman (person 2), whose mother (person 3) lives with them. She is therefore the head's mother-in-law despite being only 10 years older than him.

In all of these cases, the age difference between the in-law and the household head is not enough to classify in-laws accurately. Incorporating the age difference between the in-law and the head's spouse corrects Examples 2, 3, and 5. Examining whether married children or siblings of the head are present in the household corrects Examples 1 and 4. And using the marital status of the head also corrects Example 4.

Comparing the current and previous classification schemes

The above examples notwithstanding, the previous classification scheme relying only on age, marital status, and the household head's age was generally accurate.  Applying the old classification scheme to the 2000 5% PUMS (which contains full detail on the in-law categories), 143,027 (6.5 percent) of the in-laws would have been misclassified (see the off-diagonal cells):

  Actual code from 2000 Census  
  Parent-in-law Sibling-in-law Child-in-law Total
Relationship under old classification scheme Parent-in-law 703,458 25,531 0 743,266
Sibling-in-law 20,677 648,380 76,979 747,772
Child-in-law 0 19,840 733,107 752,947
  Total 724,135 693,751 810,086 2,227,972
Note: Weighted data from 2000 5% PUMS, using the 1990 definition of households. These figures exclude 739 individuals (16,013 when weighted) who were reported as the parents-in-law of never-married household heads. Never-married people cannot have parents-in-law, so these "in-laws" are almost certainly step-parents of the head: there was no "step-parent" option in the 2000 census relationship item, and respondents likely chose "parent-in-law" as the next-best response.

Nevertheless, the new classification scheme cuts the number of errors by almost 39 percent compared to the old classification scheme. Only 87,774 (3.9 percent) of in-laws are now misclassified:

  Actual code from 2000 Census  
  Parent-in-law Sibling-in-law Child-in-law Total
Relationship under new classification scheme Parent-in-law 717,315 16,619 166 732,192
Sibling-in-law 6,820 662,729 48,322 719,799
Child-in-law 0 14,403 761,598 776,001
  Total 724,135 693,751 810,086 2,227,972

Additionally, the new classification scheme more accurately approximates the overall distribution of in-laws in the 2000 5% PUMS:

  Actual relationship in 2000 5% PUMS Relationship under new classification scheme Relationship under old classification scheme
Parents-in-law 32.5 % 33.0 % 33.4 %
Siblings-in-law 31.1 % 32.2 % 33.6 %
Children-in-law 36.4 % 34.8 % 33.8 %
Total in-laws 100.0 % 100.0 % 100.0 %

Although the new classification scheme represents a substantial improvement over the old, users who want to use the old classification scheme can do so by running the following programs (Stata, SPSS, SAS). However, they should be aware that this code will change only the RELATE variable, not the family interrelationship variables or other variables based on them. Users who want to replicate previous research with data as it existed under the old in-law classification scheme should visit the IPUMS archive site.

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