Table 2

Ratio of self-report (after 6 months) to recorded number and duration of calls; by age, gender, education, type of phone user and level of use

NNumber of callsDuration of calls
Ratio*95% CIRatio*95% CI
Self-report (after 6 months) vs recorded960.650.53 to 0.801.110.86 to 1.42
Excluding ‘potentially unsuccessful calls’ (outgoing, ≤10 s)960.710.59 to 0.871.110.86 to 1.43
Self-report (0 months)† vs recorded960.580.48 to 0.720.900.71 to 1.15
By age (years)
 25–34400.580.49 to 0.751.170.88 to 1.57
 35–44170.540.36 to 0.820.690.56 to 1.66
 45–54210.770.44 to 1.351.450.67 to 3.14
 55–66180.820.46 to 1.480.800.40 to 1.63
p‡=0.12p‡=0.61
By gender
 Male380.740.58 to 0.940.930.69 to 1.26
 Female580.600.45 to 0.801.240.86 to 1.79
p‡=0.32p‡=0.11
By educational level
 Secondary vocational education or lower210.750.43 to 0.771.200.52 to 2.77
 Higher professional or university education630.650.51 to 0.821.120.88 to 1.43
 Postgraduate education120.530.30 to 0.950.900.39 to 2.09
p‡=0.66p‡=0.85
By type of phone user
 Study phone180.830.59 to 1.191.320.72 to 2.39
 Own phone780.620.49 to 0.781.060.80 to 1.41
p‡=0.28p‡=0.24
By level of reported phone use§
 1st tertile320.290.22 to 0.390.550.35 to 0.85
 2nd tertile310.690.53 to 0.900.930.72 to 1.20
 3rd tertile331.351.03 to 1.762.581.71 to 3.89
p‡<0.01p‡<0.01
  • *Geometric mean of ratio self-report to recorded.

  • †Self-report of current mobile phone use at baseline (0 months) before using the app.

  • ‡Adjusted for age, gender, education, type of phone user and level of phone use.

  • §Median number of calls per level: 1st: 3 calls/week; 2nd: 7; 3rd: 21. Median duration of calls per level: 1st: 7 min/week; 2nd: 37.5; 3rd: 105.