According to the Extended Twin Family Design (ETFD), multiple persons in the family are surveyed. Each type of person in the family has a specific letter and a code that are displayed in the variable names of proxy-questions and the variable ptyp. The characters are specified in Table 2.
Code | Person | ptyp |
|---|---|---|
t | twin 1 | 1 |
u | twin 2 | 2 |
s | surveyed sibling - full, half or step; for details see variable fpr0107 | 200 |
p | partner of twin 1 | 110 |
q | partner of twin 2 | 120 |
m | mother of the twins - biological, adoptive, or foster; for details see variable fpr0107 | 300 |
n | partner of the twins’ father / ‘stepmother’ | 600 |
f | father of the twins - biological, adoptive, or foster; for details see variable fpr0107 | 400 |
g | partner of the twins’ mother / ‘stepfather’ | 500 |
Table 2. Person codes. Please note: Additionally, non-participating siblings (ptyp 201 – 2xx) and other household-members (ptyp 700 – 7xx, 800) are coded in the variable ‘ptyp’.
By using the variable ptyp, the data can be restricted to a certain sample of person types that are of interest for the analysis. The variable fpr0107 describes the relation to the twins in more detail, e.g. it differentiates full siblings, half siblings and stepsiblings, etc.
Please note: The person type of twins in ptyp is always identical to the person type in the first data collection and always corresponds with the last three digits of the person ID pid. If the information on the relation to the twins was corrected in one of the most recent surveys, the variable fpr0107 in the master data set is adjusted accordingly. Thus, the information differs between ptyp and fpr0107 in very rare cases. For instance, if one twin was declared as the ‘first-born twin’ in the first data collection, but this was corrected to ‘second-born twin’ in a more recent data collection, the twin is longitudinal-consistently treated as the first-born twin in ptyp, but files as second-born twin in fpr0107. Thus the birth order of the twins is documented in fpr0107, not in ptyp. Please keep this in mind when using the variables for sample selection or analyses.