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. 2020 Jan 24;22(1):e15438. doi: 10.2196/15438

Table 2.

Differences in baseline characteristics between participants that returned and those that dropped out at the 4-month follow-up.

Variable (number of missing values) Total (N=1247) Returned (n=612) Dropped out (n=635) Test statistic P value
Age (15-19-year-olds) (0), mean (SD) 16.32 (1.07) 16.11 (0.99) 16.53 (1.10) Ua=236280.5; t1237.926=–7.090 <.001;
<.001
Gender (0), n (%)


χ21=0.5 .49

Male 586 (46.99) 282 (46.1) 304 (47.9)


Female 661 (53.01) 330 (53.9) 331 (52.1)

Educational level (0), n (%)


χ22=58.8 <.001

Compulsory secondary education 545 (43.70) 313 (51.1) 232 (36.5)


Baccalaureate program 515 (41.30) 252 (41.2) 263 (41.4)


Vocational training 187 (15.00) 47 (7.7) 140 (22.1)

Religion (3), n (%)


χ24=2.9 .57

Catholic 767 (61.65) 385 (62.9) 382 (60.4)


Protestant or Evangelical 26 (2.09) 11 (1.8) 15 (2.4)


Muslim or Islamic 18 (1.45) 9 (1.5) 9 (1.4)


Other 28 (2.25) 10 (1.6) 18 (2.8)


No religion 405 (32.56) 196 (32.1) 209 (32.9)

Ethnicity (3), n (%)


χ21=1.2 .26

Spanish 1178 (94.69) 583 (95.4) 595 (94.0)


Non-Spanish 66 (5.31) 28 (4.6) 38 (6.0)

Apgar test (55), n (%)


χ21=1.2 .28

Functional family 886 (74.33) 446 (75.7) 440 (73.0)


Dysfunctional family 306 (25.67) 143 (24.3) 163 (27.0)

Family affluence (49), n (%)


χ22=0.9 .63

Low 33 (2.76) 16 (2.7) 17 (2.8)


Medium 387 (32.30) 183 (31.0) 204 (33.5)


High 778 (64.94) 391 (66.3) 387 (63.7)

Alcohol use (0)





Binge drinking, n (%) 487 (39.05) 219 (35.8) 268 (42.2) χ21=5.6 .02

Heavy episodic drinking, n (%) 16 (1.28) 8 (1.3) 8 (1.3) χ21=0.005 .95

Weekly consumption, mean (SD) 1.45 (4.30) 1.22 (3.33) 1.68 (5.06) U=206367; t1098.665=–1.929 .01; .054

Any consumption, n (%) 832 (66.72) 404 (66.0) 428 (67.4) χ21=0.4 .55

aMann-Whitney U test.