Sarah McKenzie

Do effects of price discounts and nutrition education on food purchases vary by ethnicity, income and education? Results from a randomised, controlled trial

Background Reducing health inequalities requires interventions that work as well, if not better, among disadvantaged populations. The aim of this study was to determine if the effects of price discounts and tailored nutrition education on supermarket food purchases (percentage energy from saturated fat and healthy foods purchased) vary by ethnicity, household income and education. Method A 2×2 factorial trial of 1104 New Zealand shoppers randomised to receive a 12.5% discount on healthier foods and/or tailored nutrition education (or no intervention) for 6 months. Results There was no overall association of price discounts or nutrition education with percentage energy from saturated fat, or nutrition education with healthy food purchasing. There was an association of price discounts with healthy food purchasing (0.79 kg/week increase; 95% CI 0.43 to 1.16) that varied by ethnicity (p=0.04): European/other 1.02 kg/week (n=755; 95% CI 0.60 to 1.43); Pacific 1.20 kg/week (n=101; 95% CI 0.06 to 2.34); Māori −0.15 kg/week (n=248; 95% CI −1.10 to 0.80). This association of price discounts with healthy food purchasing did not vary by household income or education. Conclusions While a statistically significant variation by ethnicity in the effect of price discounts on food purchasing was found, the authors caution against a causal interpretation due to likely biases (eg, attrition) that differentially affected Māori and Pacific people. The study highlights the challenges in generating valid evidence by social groups for public health interventions. The null findings for tailored nutritional education across all social groups suggest that structural interventions (such as price) may be more effective.

Misclassification of the mediator matters when estimating indirect effects

Background Confounding of mediator–outcome associations resulting in collider biases causes systematic error when estimating direct and indirect effects. However, until recently little attention has been given to the impact of misclassification bias. Objective To quantify the impact of non-differential and independent misclassification of a dichotomous exposure and a dichotomous mediator on three target parameters: the total effect of exposure on outcome; the direct effect (by conditioning on the mediator); and the indirect effect (identified by the percentage reduction in the excess OR on adjusting for the mediator). Methods Simulations were conducted for varying strength of associations between exposure, mediator and outcome, varying ratios of exposed to unexposed and mediator present to mediator absent, and varying sensitivity and specificity of exposure and mediator classification. Results ORs before (total effect) and after adjustment (direct effect) for the mediator are both biased towards the null by non-differential misclassification of the exposure, but the percentage reduction in the excess OR is little affected by misclassification of exposure. Conversely, misclassification of the mediator rapidly biases the percentage reduction of the excess OR (indirect effect) downwards. Conclusions If the research objective is to quantify the proportion of the total association that is due to mediation (ie, indirect effect), then minimising non-differential misclassification bias of the mediator is more important than that for the exposure. Misclassification bias is an important source of error when estimating direct and indirect effects.

Differential loss of participants does not necessarily cause selection bias

Background: Most research is affected by differential participation, where individuals who do not participate have different characteristics to those who do. This is often assumed to induce selection bias. However, selection bias only occurs if the exposure‐outcome association differs for participants compared to non‐participants. We empirically demonstrate that selection bias does not necessarily occur when participation varies in a study.

Effects of childhood socioeconomic position on subjective health and health behaviours in adulthood: how much is mediated by adult socioeconomic position?

BackgroundAdult socioeconomic position (SEP) is one of the most frequently hypothesised indirect pathways between childhood SEP and adult health. However, few studies that explore the indirect associations between childhood SEP and adult health systematically investigate the mediating role of multiple individual measures of adult SEP for different health outcomes. We examine the potential mediating role of individual measures of adult SEP in the associations of childhood SEP with self-rated health, self-reported mental health, current smoking status and binge drinking in adulthood.MethodsData came from 10,010 adults aged 25-64 years at Wave 3 of the Survey of Family, Income and Employment in New Zealand. The associations between childhood SEP (assessed using retrospective information on parental occupation) and self-rated health, self-reported psychological distress, current smoking status and binge drinking were determined using logistic regression. Models were adjusted individually for the mediating effects of education, household income, labour market activity and area deprivation.ResultsRespondents from a lower childhood SEP had a greater odds of being a current smoker (OR 1.70 95% CI 1.42-2.03), reporting poorer health (OR 1.82 95% CI 1.39-2.38) or higher psychological distress (OR 1.60 95% CI 1.20-2.14) compared to those from a higher childhood SEP. Two-thirds to three quarters of the association of childhood SEP with current smoking (78%), and psychological distress (66%) and over half the association with poor self-rated health (55%) was explained by educational attainment. Other adult socioeconomic measures had much smaller mediating effects.ConclusionsThis study suggests that the association between childhood SEP and self-rated health, psychological distress and current smoking in adulthood is largely explained through an indirect socioeconomic pathway involving education. However, household income, area deprivation and labour market activity are still likely to be important as they are intermediaries in turn, in the socioeconomic pathway between education and health.

Chronic exposure to schistosome eggs reduces serum cholesterol but has no effect on atherosclerotic lesion development

Previous studies have shown that people infected with schistosomiasis have lower levels of serum cholesterol than uninfected controls. To better understand the impact of this parasitic infection on serum cholesterol levels and on atherosclerotic lesion development induced by hypercholesterolemia, apolipoprotein E (ApoE)‐deficient mice were chronically exposed to the eggs of Schistosoma mansoni over a period of 16 weeks. Total serum cholesterol and low‐density lipoprotein (LDL) were reduced in egg‐exposed ApoE‐deficient mice fed a diet high in cholesterol compared to unexposed controls. However, exposure to eggs had no effect on atherosclerotic lesion size or progression in ApoE‐deficient mice. Macrophages isolated from egg‐exposed mice had an enhanced ability to take up LDL but not acetylated LDL (acLDL). This study suggests that schistosome eggs alone may alter serum lipid profiles through enhancing LDL uptake by macrophages, but these changes do not ultimately affect atherosclerotic lesion development.

Do changes in socioeconomic factors lead to changes in mental health? Findings from three waves of a population based panel study

Background There has been little investigation of changes in socioeconomic measures and mental health (MH)/illness over time within individuals using methods that control for time-invariant unobserved confounders. We investigate whether changes in multiple socioeconomic measures are associated with self-reported MH using fixed effects methods to control for unobserved time-invariant confounding. Methods Data from three waves of a panel study with information on MH, psychological distress, labour force status, household income, area and individual deprivation. Fixed effects regression modelling was used to explore whether changes in socioeconomic exposures were associated with changes in MH. We also compared increases and decreases in exposure with changes in MH using first difference models. Results Respondents who moved into inactive labour force status experienced a 1.34 unit (95% CI −1.85 to −0.82) decline in SF-36 MH score and a 0.50 unit (95% CI 0.34 to 0.67) increase in psychological distress score. An increase in individual deprivation was associated with a 1.47 unit (95% CI −1.67 to −1.28) decline in MH score and a 0.57 unit (95% CI 0.51 to 0.63) increase in psychological distress. Increasing and decreasing levels of individual deprivation were associated with significant changes in both outcomes. Conclusions This paper suggests that moving from employment to inactivity and changes in levels of individual deprivation may be more important for short-term MH outcomes than changes in household income or area deprivation. Providing short-term social and economic support for those experiencing financial/material hardship should be considered in interventions to reduce inequalities in MH.

Does transition into parenthood lead to changes in mental health? Findings from three waves of a population based panel study

Background Longitudinal studies specifically looking at the transition into parenthood and changes in mental health in the general population are scarce. This study aimed to investigate the impact of transition into parenthood on mental health and psychological distress using longitudinal survey data. Methods The analysis used three waves from the longitudinal Survey of Family, Income and Employment. Parenthood was classified as first time parent (first and only child <12 months at interview date), subsequent parent (child <12 months and other children in the family), existing parent (no children <12 months but other existing children in the family) and not a parent. We used fixed effects generalised linear modelling, controlling for all time-invariant and time-varying sources of confounding in a sample of 6670 adults within families. Results After adjusting for confounding from time-varying partner status, area deprivation, labour force status and household income, those who became first time parents reported an increase in mental health (β 1.22, 95% CI −0.06 to 2.50; mean=83.8, SD=14.1) and a decrease in psychological distress (β −0.70 95% CI −1.10 to −0.29; mean=13.4, SD=5.0). Subsequent parents reported a decrease in psychological distress (β −0.60 95% CI −0.95 to −0.24). Conclusions Our findings suggest that a transition into parenthood for the first time leads to changes in mental health and psychological distress. Understanding the relationship between becoming a parent and mental health outcomes is important given that parental mental health is integral to effective parenting.

Income-related health inequalities in working age men and women in Australia and New Zealand

Objective : To examine income‐related inequalities in health in working age men and women in Australia and New Zealand.

Ethical considerations in sensitive suicide research reliant on non-clinical researchers

The impact on researchers of working with sensitive data is often not considered by ethics committees when approving research proposals. We conducted interviews with eight research assistants processing clinical notes on emergency department presentations for deliberate self-harm and suicide attempts during a suicide prevention trial. Common experiences of working with the data included feeling unprepared for the level of detail in the records, being drawn deeply into individual stories, emotional exhaustion from the cumulative exposure to the data over long periods of time while working alone, and experiencing a heightened awareness of the fragility of life and the need for safety. The research assistants also reported on some of the strategies they had developed to cope with the sensitive nature of the data and the demands of the work. The ethical implications for suicide research reliant on non-clinically trained researchers exploring sensitive data are considered. These include the need for research leaders and ethics committees to be aware of the potential adverse mental health impacts for these researchers examining sensitive data and to make appropriate arrangements to minimize the mental health impacts of such work.

Do changes in social and economic factors lead to changes in drinking behavior in young adults? Findings from three waves of a population based panel study

BackgroundSocial and economic measures in early childhood or adolescence appear to be associated with drinking behavior in young adulthood. Yet, there has been little investigation to what extent drinking behavior of young adults changes within young adulthood when they experience changes in social and economic measures in this significant period of their life.MethodsThe impact of changes in living arrangement, education/employment, income, and deprivation on changes in average weekly alcohol units of consumption and frequency of hazardous drinking sessions per month in young adults was investigated. In total, 1,260 respondents of the New Zealand longitudinal Survey of Family, Income and Employment (SoFIE) aged 18-24 years at baseline were included.ResultsYoung adults who moved from a family household into a single household experienced an increase of 2.32 (95% CI 1.02 to 3.63) standard drinks per week, whereas those young adults who became parents experienced a reduction in both average weekly units of alcohol (β = -3.84, 95% CI -5.44 to -2.23) and in the frequency of hazardous drinking sessions per month (β = -1.17, 95% CI -1.76 to -0.57). A one unit increase in individual deprivation in young adulthood was associated with a 0.48 (95% CI 0.10 to 0.86) unit increase in average alcohol consumption and a modest increase in the frequency of hazardous drinking sessions (β = 0.25, 95% CI 0.11 to 0.39).ConclusionsThis analysis suggests that changes in living arrangement and individual deprivation are associated with changes in young adult’s drinking behaviors. Alcohol harm-minimization interventions therefore need to take into account the social and economic context of young people’s lives to be effective.