Table 2

Distribution of migrants by patterns of migration

Groupn (%)Mean (SD)*Median (IQR)*Range (min–max)
By age at first migration585 (100%)14.7 (9)14 (7)
 ≤12 years old when first migrated225 (38.4%)8.2 (3.2)8 (5)
 >12 years old when first migrated360 (61.6%)18.7 (9)16 (4)
By length of residence in urban area (in years)559 (100%)32 (10.5)31 (14)
 Migrant <20 years in urban area§53 (9.5%)15 (4.1)16 (4)
 Migrant 20–29 years in urban area203 (36.3%)25.1 (2.6)25 (4)
 Migrant 30–39 years in urban area169 (30.2%)34.4 (2.9)34 (5)
 Migrant ≥40 years in urban area134 (24%)46.1 (6.3)44 (6)
By lifetime exposure to urban area559 (100%)67.7 (15.1)69.4 (18.3)0–100
 Quartile 1, lowest141 (25.2%)47.8 (11.6)51.8 (14.6)0–59.5
 Quartile 2139 (24.9%)64.8 (2.9)65 (4.9)59.5–69.4
 Quartile 3142 (25.4%)73.7 (2.4)73.5 (4)69.6–77.8
 Quartile 4, highest137 (24.5%)85 (5.7)83.6 (7.7)78–100
  • * Summary statistics, mean (SD) and median (IQR), are provided for this variable in relation to each group. All units for descriptive statistics correspond to absolute number of years or percentages of total age in the case of lifetime exposure to urban area.

  • Sub-classification based on 585/589 (99.3%) observations in the migrant group.

  • Sub-classification based on 559/589 (95%) observations in the migrant group.

  • § In order to ensure sufficient numbers in each strata, the first two groups, ‘<10 years in urban area’ (n=6) and ‘10–19 years in urban area’ (n=47), were merged into a single stratum: ‘<20 years in urban area’.

  • Quartiles were created based on proportion (percentage) of lifetime exposure to urban environment, defined as number of years lived in an urban area divided by age. Sub-classification based on 559/589 (95%) observations in the migrant group.