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Gu D, Feng Q, Sautter JM and Qiu L

Table 1. Classification of urban exposure under different combinations of variables
Four-type classification Eight-type classification Fourteen-type classification
Measures: Measures: Measures:
1. Rural/urban birth place 1. Rural/urban birth place 1. Rural/urban birth place
2. Rural/urban residential status at 2. Rural/urban residential status at the first 2. Rural/urban residential status at the first interview
the first interview interview
3. Rural/urban primary lifetime occupation (PLO) 3. Rural/urban primary lifetime occupation (PLO)
4. Yes/no moved to another county/city (migration)

Types: Types: Types:
1. Rural-rural, r-PLO 1. No exposure, no migration
(no exposure) 2. No exposure, migrated
1. Rural-rural: rural birth place and
rural status at the first interview
2. Rural-rural, u-PLO 3. Mid-life-only exposure, no migration
(mid-life-only exposure) 4. Mid-life-only exposure, migrated

3. Rural-urban, r-PLO 5. Late-life-only exposure, no migration
(late-life-only exposure) 6. Late-life-only exposure, migrated
2. Rural-urban: rural birth place
and urban status at the first
interview 4. Rural-urban, u-PLO 7. Mid-late-life exposure, no migration
(mid-late-life exposure) 8. Mid-late-life exposure, migrated

5. Urban-rural, r-PLO 9. Early-life exposure, yes/no migration
(early-life-only exposure)
3. Urban-rural: urban birth
place and rural status at the first
interview 6. Urban-rural, u-PLO 10. Early-mid-life exposure, yes/no migration
(early-mid-life exposure)

7. Urban-urban, r-PLO 11. Early- & late-life exposure, no migration
(early- & late-life exposure) 12. Early- & late-life exposure, migrated
4. Urban-urban: urban birth
place and urban status at the first
interview 8. Urban-urban, u-PLO 13. Full exposure, no migration
(full exposure) 14. Full exposure, migrated

no), current marital status (married vs. no), coresidence with children (yes vs. no),
and frequency of participation in six leisure activities. Frequency of participation in
leisure activities includes doing housework, gardening, raising domestic animals or
poultry, reading books/newspapers, watching TV/listening to radio, and any other
personal outdoor activities. Each physical activity was measured on a five-point Likert
scale (from never to almost daily) and the values were summed; following previous
research, we categorized respondents into three groups of participation: low level (never
involved in these activities), high level (involved 1–7 times per week in at least one
activity), and medium level (the remaining respondents) (Zhao, Sautter, Qiu, et al.,
2017).
We also controlled for baseline health. Disability in activities of daily living (ADL)
was measured by six activities: (a) bathing, (b) dressing, (c) indoor transferring, (d)
toileting, (e) eating, and (f) continence (Zeng, Gu and Land, 2007). Each item had
three response categories: “able to do without help,” “need some help,” and “need full
help.” The respondents were considered as ADL disabled (coded as 1) if they reported
needing any help in performing any of the six items; otherwise they were coded as 0.
Disability in IADL was adopted from the Katz scale (Gu, 2008), which included eight

International Journal of Population Studies 2017, Volume 3, Issue 1 7