Specifically, these areas included home life (DIFHOME), friendships (DIFFRIEND), and leisure (DIFLEISURE). Other questions collected information about whether the difficulties upset or distressed the child (DIFUPSET) and burdened the child's family (DIFBURDEN).

As the Appendix on SDQ in the 2001 and 2003-2004 Codebook of the NHIS public use files explains:

• emotional symptoms;

• conduct problems;

• hyperactive behavior;

• peer relationships;

• prosocial behavior.

DIFLEARN was an element in the second part of the SDQ, which the same source describes as follows:

More information on the SDQ-EX is available at www.sdqinfo.org. This source describes the second section of the SDQ-EX, which includes DIFLEARN, as the "Impact Supplement."

In the 2001 and 2003-2004 NHIS, if parents said (in EMODIFF) that the child had minor, definite, or severe difficulties with emotions, concentration, behavior, or getting along with others, they were asked how long the difficulties had been present (DIFMOS). In those three years, interviewers asked follow-up questions about the impact of the difficulties was one month or longer. The follow-up questions about the impact of the difficulties on the child's life were the basis of the following variables:

• Difficulties upset or distress child (DIFUPSET)

• Child's difficulties interfere with home life (DIFHOME)

• Child's difficulties interfere with friendships (DIFFRIEND)

• Child's difficulties interfere with classroom learning (DIFLEARN)

• Child's difficulties interfere with leisure activities (DIFLEISURE)

DIFUPSET was based on the question, "Do the difficulties upset or distress your child?" The remaining four variables were based on the query, "Do the difficulties interfere with your child's everyday life in the following areas: Home life? Friendships? Classroom learning? Leisure activities?"

If parents responded "no" to the opening question about whether the child had difficulties with emotions, concentration, behavior, or getting along with others (EMODIFF), none of these five questions were asked. In such cases, when parents "are not asked to complete the questions on resultant distress or impairment," the Scoring Guide states, "the impact score is automatically scored zero." The same is true when, in DIFMOS, parents reported that difficulty in these areas lasted less than 1 month (and thereby avoided these follow-up questions on "resultant distress or impairment"). To simplify the calculation of the impact score for such persons, IPUMS NHIS staff recoded those who answered "no" to EMODIFF and those who answered "less than 1 month" to DIFMOS to the code "No difficulty or no difficulty for greater than or equal to 1 month" (a code of 00).

Contrary to 2001, 2003, and 2004, beginning in 2019, interviewers asked the follow-up questions about the impact of the difficulties on the child’s life (DIFUPSET, DIFHOME, DIFFRIEND, DIFLEARN, and DIFLEISURE), no matter how long the difficulties had been present, as reported in DIFMOS.

To increase congruency with the 2001, 2003, and 2004 samples, IPUMS NHIS staff recoded those who answered "no difficulty" to EMODIFF to the code 00, "No difficulty or no difficulty for greater than or equal to 1 month" in 2019 forward. When using the impact variables to calculate an impact score, this approach is compatible with guidelines from the SDQ Scoring Guide, which state that when respondents answer "no" to EMODIFF, they are not asked the follow-up questions on distress or impairment and the impact score is automatically set to zero.

IPUMS NHIS offers the impact score as the variable DIFSCORE. Prior to 2019, IPUMS NHIS staff constructed DIFSCORE by following the process listed below. Beginning in 2019, NHIS began offering the impact score as a variable constructed by following the guidelines in the SDQ Scoring Guide. DIFSCORE sums the scores received across DIFUPSET, DIFHOME, DIFFRIEND, DIFLEARN, and DIFLEISURE to indicate the impact of the difficulties on the child’s life. Users should note that, due to the changes in universe for the five impact variables, those persons in universe for an impact score also change over time. In 2001, 2003, and 2004, only those who answered that their difficulties lasted greater than or equal to 1 month in DIFMOS could be asked the impact questions and therefore have an impact score calculated. In 2019 forward, all persons who indicated they had difficulties in EMODIFF were asked the five impact questions. Therefore, someone who indicated their difficulties lasted less than 1 month could have a non-zero impact score in 2019 but would have a score of 0 in the earlier years.

The SDQ Scoring Guide provides guidance on how responses for these five variables "can be summed to generate an impact score that ranges from 0 to 10 for the parent-completed version." Under these guidelines, the responses "not at all" and "a little" are given a score of 0; a response of "a medium amount" is given a score of 1; and a response of "a great deal" is given a score of 2. For each of these variables, a score of 0 implies the least impact from the child's difficulty, and a score of 2 implies the greatest impact from the child's difficulty. If the scores for these five variables are summed, the total ranges from 0 to 10, with 0 implying the least impact from the child's difficulties and 10 implying the greatest impact from the child's difficulties.

Users may choose to manually calculate an impact score instead of using DIFSCORE. The five variables that can be summed to create a total impact score receive codes in IPUMS NHIS that facilitate this scoring process. Responses that should receive a score of 0 in the scoring process--namely, "not at all" or "a little"--receive a code of 0 in the first digit. In addition, sample children with no reported difficulties (in EMODIFF) or with difficulties lasting "less than one month" (code 1 in DIFMOS) for 2001, 2003, and 2004 also receive a code of 0 in the first digit in these five variables. (The three different categories, "No difficulty or no difficulty for greater than or equal to 1 month," "not at all," and "a little" can still be distinguished from each other by the respective values of 0, 1, and 2 in the second digit.) The response "a medium amount," which should receive a score of 1, receives a code of 1 in the first digit (and a code of 0 in the second digit). The response "a great deal," which should receive a score of 2, receives a code of 2 in the first digit (and a code of 0 in the second digit). Cases which should be excluded from this summing of scores--that is, not in universe cases consisting of persons other than sample children age 4-17, and cases with a response of "unknown"--all receive a code of 9 in the first digit (with the second digit distinguishing between those not in the variable universe and unknowns).

Put succinctly, to calculate an "impact score" for the child's difficulties, researchers should 1) exclude cases beginning with a code of 9; 2) group together other categories that share a common first digit; 3) sum the scores across the five variables, using only the first digit of the codes for each variable. The result will range from 0 to 10.

According to the SDQ Scoring Guide, the impact score can be used as a continuous variable, but it is sometimes convenient to classify it into broader categories for easier interpretation of results. Under the original three-band categorization, total impact scores can be identified as normal, borderline, or abnormal: a total impact score of 2 or more is abnormal; a score of 1 is borderline; and a score of 0 is normal. Under the newer four-band categorization, total impact scores can be identified as close to average, slightly raised, high, or very high: a total impact score of 0 is close to average; a score of 1 is slightly raised; a score of 2 is high; and a score of 3 or higher is very high.