Changes to the protocol
Chapter 6 First follow-up
Introduction
The first follow-up was scheduled at 3 months after the end of the intervention, which was 6 months after the baseline assessment, as the text messages were sent over a 12-week period. The aim was to detect whether or not there were short-term changes in alcohol consumption. This was intended to aid the interpretation of any changes in the frequency of binge drinking at 12 months post intervention, which is the primary outcome measure for the trial. This chapter presents a descriptive analysis of two prespecified secondary outcomes: the proportion of men with≥3 occasions of binge drinking (>8 units of alcohol) and the proportion of men with≥3 occasions of heavy binge drinking (>16 units of alcohol) in the preceding 28 days. It also explores whether or not loss to follow-up could have introduced bias into the observed results.
Results
In total, 737 of the 825 men (89.3%) were followed up. Retention rates were almost identical for the two treatment groups: 89.1% (366/411) for the intervention group and 89.6% (371/414) for the control group. There was a marked, and similar, fall in the two treatment groups of the proportion of men with≥3 occasions of binge drinking: the intervention group fell by 37.4% and the control group fell by 40.5% (Table 15). The proportion of men with≥3 occasions of heavy binge drinking followed a similar pattern, with large falls in both groups. The falls in the proportions of men with binge and heavy binge-drinking sessions are accompanied by falls in the mean number of these drinking sessions. For example, in the intervention group, the mean number of binge-drinking sessions fell from 6.49 to 3.82 (i.e. by 2.67 sessions) and the mean number of heavy binge-drinking sessions fell by 1.65 sessions. As a result of these falls, the mean number of non-drinking days increased by 2.2 days. The same pattern of changes is seen in the control group.
TABLE 15 Comparison of baseline and first follow-up drinking habits by treatment arm
Alcohol consumption in the previous 28 days
Group Intervention Control Baseline (N=366) 3-month follow-up (N=366) Baseline (N=371) 3-month follow-up (N=371) Percentage of men with≥3 occasions of binge drinking
(>8 units of alcohol)
82.2 44.8 85.2 44.7
Percentage of men with≥3 occasions of heavy binge drinking (>16 units of alcohol)a
46.2 22.1 48.3 20.2
Mean number of binge-drinking sessions (>8 units of alcohol) (SD)
6.49 (5.3) 3.82 (5.4) 6.57 (5.2) 3.85 (5.4) Mean number of heavy binge-drinking sessions
(>16 units of alcohol) (SD)
3.58 (5.1) 1.93 (4.4) 3.55 (4.6) 1.74 (4.2)
Mean number of alcohol-free days (SD) 19.9 (5.9) 22.1 (6.0) 19.9 (5.8) 21.8 (6.3) Mean consumption in previous 28 days (units) (SD) 131.6 (132.0) 77.6 (113.3) 133.0 (134.3) 78.7 (115.7) Proportion of total units consumed during binge-drinking
sessions (>8 units of alcohol) (%)
92.3 61.8 92.5 64.2
The mean consumption of alcohol in the previous 28 days also fell substantially and by similar amounts in the two groups: 54.0 units in the intervention group and 54.3 units in the control group (seeTable 15). The fall in mean consumption occurred through falls in the frequency of binge drinking and reductions in the amount consumed in binge-drinking sessions. Individuals differed in the way in which their consumption changed (Table 16). Thus, two-thirds of the 192 men who drank>150 units of alcohol at baseline reduced their consumption at follow-up, and 60 of these men reduced to≤50 units of alcohol. Among the men who drank between 50 and 100 units, a few (n=38), increased their consumption, but most (n=164), reduced their consumption. Overall, at every category of baseline alcohol consumption, most men had reduced their consumption at follow-up. Approximately 10% of the men in each category reduced their consumption to zero.
Loss to follow-up
The drinking patterns at baseline among those lost to follow-up was explored to identify whether or not bias could have been introduced.Table 17shows that those lost to follow-up in the two groups had very similar drinking patterns at baseline and none of the differences approached statistical significance.
Although there are small differences between the treatment groups, these sometimes favour one group and sometimes favour the other.
The men who were not followed up differed slightly in their drinking patterns from those who were followed up (Table 18). Those not followed up were more likely to have≥3 binge, and heavy binge, drinking sessions. Their mean alcohol consumption was also higher. However, although the direction of effect is consistent, all of these differences were small and none was statistically significant.
The men who were not followed up differed markedly from those followed up in terms of their
demographic characteristics (Table 19). Thus, a substantially larger proportion of those lost to follow-up were single, were unemployed or had lower educational attainment. They were also, on average, younger and were much more likely to have been recruited by TSS. All of these differences were statistically significant.
Discussion
This chapter has presented the results of the interim follow-up. Only two secondary outcome measures were prespecified in the protocol to be assessed at this follow-up. As such, it would be inappropriate to draw conclusions about effectiveness at this stage. However, these analyses found that, at the interim follow-up, the differences between treatment groups on all measures of alcohol consumption (amounts consumed and frequency of binge drinking) were small. Conventional alcohol brief interventions in primary care show a difference in the frequency of binge drinking of 11% and a difference in mean consumption of 10%.5In contrast, the differences seen in this interim analysis are much smaller.
TABLE 16 Comparison of consumption (over 28 days) at baseline and first follow-up
Baseline: participants’consumption in previous 28 days (units)
First follow-up: participants’consumption in previous 28 days (units) Total (units) 0 ≤50 >50–100 >100–150 >150 ≤50 19 85 18 7 5 134 >50–100 25 139 67 23 15 269 >100–150 12 61 38 16 15 142 >150 17 43 42 29 61 192 Total 73 328 165 75 96 737 FIRST FOLLOW-UP
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TABLE 17 Baseline drinking patterns of men who were not followed up, by treatment group Factor Group Total (N=88), mean (SD) p-value Intervention (N=45) Control (N=43) Percentage of men with≥3 occasions of binge drinking
(>8 units of alcohol)
91.1 88.4 89.8 0.672a
Percentage of men with≥3 occasions of binge drinking (>16 units of alcohol)
48.9 51.2 50.0 0.831a
Mean consumption in previous 28 days (units) (SD) 145.0 (138.6) 150.8 (122.0) 147.8 (130.0) 0.835b Proportion of total units that are consumed during
binge-drinking sessions (>8 units of alcohol), % (SD)
93.1 (14.4) 93.2 (18.0) 93.1 (16.2) 0.977b
Mean number of binge-drinking sessions (>8 units of alcohol) (SD)
6.71 (5.1) 7.28 (5.3) 6.99 (5.2) 0.611b Mean number of heavy binge-drinking sessions (>16 units
of alcohol) (SD)
3.33 (4.4) 3.98 (4.9) 3.65 (4.6) 0.517b
Mean number of alcohol-free days (SD) 19.64 (5.9) 19.40 (5.8) 19.52 (5.8) 0.843b Frequency of being unable to remember what happened the night before because of drinking,n(%)
Never 25 (55.6) 26 (60.5) 51 (58.0) 0.283a
Less than monthly 15 (33.3) 9 (20.9) 24 (27.3)
Monthly 4 (8.9) 8 (18.6) 12 (13.6)
Weekly or more 1 (2.2) 0 (0.0) 1 (1.1)
a Chi-squared test. b t-test.
TABLE 18 Baseline alcohol consumption of men who were and were not followed up at 3 months post intervention
Factor
Followed up
p-value No (N=88) Yes (N=737)
Percentage of men with≥3 occasions of binge drinking (>8 units of alcohol) 89.8 83.7 0.139a Percentage of men with≥3 occasions of binge drinking (>16 units of alcohol) 50.0 47.2 0.621a Mean consumption in previous 28 days (units) (SD) 147.8 (130.0) 132.3 (133.1) 0.301b Proportion of total units consumed during binge-drinking sessions
(>8 units of alcohol), % (SD)
93.1 (16.2) 92.4 (15.8) 0.702b Mean number of binge-drinking sessions (>8 units of alcohol) (SD) 6.99 (5.2) 6.53 (5.2) 0.439b Mean number of heavy binge-drinking sessions (>16 units of alcohol) (SD) 3.65 (4.6) 3.56 (8.4) 0.878b Mean number of alcohol-free days (SD) 19.52 (5.8) 19.92 (5.9) 0.546b Frequency of being unable to remember what happened the night before because of drinking,n(%)
Never 51 (58.0) 451 (61.2) 0.175a
Less than monthly 24 (27.3) 211 (28.6)
Monthly 12 (13.6) 54 (7.3)
Weekly or more 1 (1.1) 21 (2.8)
a Chi-squared test. b t-test
The most striking finding from these analyses was the large fall in all measures of alcohol consumption seen in both groups. Large falls are often seen in the control groups of trials of alcohol brief interventions.135,161 Possible explanations for these falls will not be explored here. Instead, a thorough review of possible explanations for the findings from the interim and final follow-up analyses will be presented inChapter 8. The retention rate was high at 3 months post intervention. This could be a consequence of the use of several evidence-based techniques such as financial incentives, maintaining regular contact, and multiple methods of and attempts at contact. It is notable that during the process of getting in touch only two men requested not to be contacted again, suggesting that the multiple attempts caused little or no inconvenience to the participants.
The possibility of bias due to loss to follow-up in the interim analyses is low. Loss to follow-up in this study was low in comparison with that found in conventional brief interventions in which outcomes were measured 6 months after baseline.5Retention rates were high and almost identical in the two treatment arms. Furthermore, those lost to follow-up in the two treatment arms were almost identical in their levels of baseline alcohol consumption. Finally, those who completed this follow-up had broadly similar levels of alcohol consumption at baseline to those who were not followed up. These findings suggest that loss-to-follow-up bias is unlikely to be an explanation for the similarity in groups at the interim follow-up.
The men who were lost to follow-up were markedly different in terms of demographic characteristics from those retained in the study. This suggests that mechanisms other than heavy alcohol consumption may be responsible for the loss of these men. One possibility is that two related factors, life stresses and low income, explain the loss to follow-up.
TABLE 19 Demographic characteristics of men who were and were not followed up at 3 months post intervention
Characteristic
Followed up,n(%)
p-value No (N=88) Yes (N=737)
Age (years), mean (SD) 32.3 (5.1) 34.9 (5.4) <0.001a Recruitment method
General practice registers 24 (27.3) 403 (54.7) <0.001b
TSS 64 (72.7) 334 (45.3)
Marital statusc
Married/lives with a partner 32 (36.4) 416 (56.5) <0.001b
Single 56 (63.6) 320 (43.5) SIMD decile 1–2 (most deprived) 59 (67.0) 577 (78.3) 0.018b ≥3 29 (33.0) 160 (21.7) Employment status Employed 29 (33.0) 499 (67.7) <0.001b Unemployed 59 (67.0) 238 (32.3)
Highest educational attainment
High school 57 (64.8) 453 (61.5) 0.027b
Vocational qualification/further training 30 (34.1) 214 (29.0)
University degree 1 (1.1) 70 (9.5)
a t-test.
b Chi-squared test.
c Marital status was not recorded for one man. FIRST FOLLOW-UP
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