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Table 1 Variables considered for inclusion in the model

From: Factors associated with the effectiveness and reach of NHS stop smoking services for pregnant women in England

Independent variable Description, source & justification Dependent variable tested against
The mean index of multiple deprivation (IMD) Continuous variable. SSSP level IMD was used. IMD score ranged from 9 to 43, with higher score indicating greater deprivation. Taken from UK Data Service Census Support. [22] Measures of deprivation were inversely associated with pregnant smokers’ cessation in a recent large RCT. [34] SSS for non-pregnant smokers have successfully attracted smokers from lower socio economic groups. [31] Reach, [31] Effectiveness [34]
Survey data
 Whether or not mandatory midwifery training in local hospitals included smoking cessation Binary variable. SSSP in which midwifes received smoking cessation training versus those who did not. It was hypothesised that training could influence propensity for midwives to refer women to SSSP and initial midwife contacts may be more effective at promoting smoking cessation. Reach, Effectiveness
 Whether or not identification of smokers used CO monitoring and an opt-out referral pathway Binary variable. SSSP in which the opt-out referral pathway was used versus those that did not. This kind of referral pathway has been shown to increase SSSP referrals (and hence Reach) [35] and has been associated with better service outcomes in an observational study. [36] Reach, [35] Effectiveness [36]
 Whether or not the Commissioning for Quality and Innovation (CQUIN) framework [37] was in place for referrals to the SSSP Binary variable. SSSP in which either the CQUIN was in place for recording smoking status, referrals, providing brief advice or any other, versus not being so. We hypothesised that having such a local policy in place which encouraged identification of smokers could result in greater Reach. Reach
 Whether the SSSP used social networking sites to engage women Binary variable. SSSP in which specialist cessation service offered was advertised using any social networks. We hypothesised that services which pro-actively attempted to engage with women in this way may have greater Reach. Reach
 Whether SSSP staff initially contacted referred pregnant smokers by phone Binary variable. SSSP that initially contacted women via phone as opposed to letter, SMS, email, face-to-face contact, home visit or if pregnant women contacted the service. We hypothesised that the manner of initial contact could have consequences for Reach. Reach
 Whether the majority of one-to-one support offered by the SSSP was at home or in the clinic Binary variable. SSSP that offered more behavioural support at home as opposed that offered in the clinic. We hypothesised that offering support at home might influence Reach; there is evidence that for non-pregnant smokers, location of support provision can influence the Effectiveness of support delivered. [38] Reach, Effectiveness [38]
 Whether the SSSP centre offered couple or family support Binary variable. SSSP that provided behavioural support in the form of couple or family support versus those that did not. We hypothesised that offering partner support might increase the likelihood of women attending SSSP (Reach); partner support is a key variable influencing pregnant women’s success in cessation attempts. [39] Reach, Effectiveness [39]
 Whether there were any financial incentives offered by the SSSP Binary variable. SSSP that provided an incentive scheme for pregnant women versus those that did not. We hypothesised that the availability of incentives might affect women’s propensity to engage with services; a recent trial has shown these to be effective in the SSSP context. [40] Reach, Effectiveness [40]
 Whether self-referral patients accounted for one of the top three referral methods to the SSSP Binary variable. SSSP in which self-referral was at least the third most popular referral method, versus those in which it was not. We hypothesised that flexibility in accepting referrals might affect Reach. Reach
 Whether the SSSP offered ‘dual therapy’ nicotine replacement therapy (NRT) (i.e. longer and shorter acting preparations used together) Binary variable. SSSP that offered dual therapy NRT with or without behavioural support versus SSSP that did not. Although there is no evidence that standard dose NRT works we hypothesised that higher doses from use of ‘dual therapy’ might be effective. Effectiveness
Census data
 In the absence of a strong evidence base, all of the following variables were considered to have the potential to affect either Effectiveness or Reach
 The proportion of women in the area covered by the SSSP not of white or mixed ethnicity Continuous variable. National census data aggregated at the SSSP level. [21] We hypothesised women who did not identify as white or mixed ethnicity might be less likely to smoke and may be less likely to seek help to quit smoking. Effectiveness, Reach
 The proportion of people aged ≥16 years in the area covered by the SSSP with no qualifications Continuous variable. National census data aggregated at the SSSP level. [21] We hypothesised that the level of education is inversely associated with the odds of cessation, and may also be associated with awareness of harms and thus, making a quit attempt. Effectiveness, Reach
 The proportion of people in the area covered by the SSSP with dependent children Continuous variable. National census data aggregated at the SSSP level. [21] We hypothesised that having dependent children may decrease the odds of being able to attend clinic visits. Effectiveness, Reach
 The proportion of people in the area covered by the SSSP in managerial or professional occupations Continuous variable. National census data aggregated at the SSSP level. [21] We hypothesised women who are in managerial or professional occupations may have higher levels of education, and be less likely to smoke. They may view themselves as less likely to need help and not attend SSSP. Effectiveness, Reach
 The proportion of people in the area covered by the SSSP aged <18 years Continuous variable. National census data aggregated at the SSSP level. [21] We hypothesised being of younger age may affect women’s likelihood of quitting smoking. Effectiveness, Reach