Handling Missing Values in Interrupted Time Series Analysis of Longitudinal Individual-Level Data

Changes in sodium levels in Australian packaged foods between 2014 and 2019: an interrupted time series analysis of the impact of the Victorian Salt Reduction Partnership's media advocacy strategy

BACKGROUND

The Victorian Salt Reduction Partnership (VSRP) implemented a media advocacy strategy (intervention) to stimulate food manufacturers to reduce sodium levels across targeted Australian packaged foods between 2017 and 2019. This study assessed changes in sodium levels of targeted and non-targeted packaged foods during the intervention (2017 to 2019) compared to before the intervention (2014 to 2016) in Australia.

METHODS

Annually collected branded-food composition data from 2014 to 2019 were used. Interrupted time series analyses was conducted to compare the trend in sodium levels in packaged foods during the intervention (2017-2019) to the trend in the pre-intervention period (2014-2016). The difference between these trends was derived to estimate the effect of the intervention.

RESULTS

A total of 90,807 products were included in the analysis, of which 14,743 were targeted by the intervention. The difference in before and during intervention trends between targeted and non-targeted food categories was 2.59 mg/100 g (95% CI: -13.88 to 19.06). There was a difference in the pre-intervention slope (2014, 2015, 2016) and intervention slope (2017, 2018, 2019) for four of 17 targeted food categories. There was a decrease in sodium levels (mg/100 g) in one food category: frozen ready meals (-13.47; 95% CI: -25.40 to -1.53), and an increase in three categories: flat bread (20.46; 95% CI: 9.11 to 31.81), plain dry biscuits (24.53; 95% CI: 5.87 to 43.19), and bacon (44.54; 95% CI: 6.36 to 82.72). For the other 13 targeted categories, the difference in slopes crossed the line of null effect.

CONCLUSIONS

The VSRP's media advocacy strategy did not result in a meaningful reduction in sodium levels of targeted packaged food products during the intervention years compared to trends in sodium levels before the intervention. Our study suggests media advocacy activities highlighting the differences in sodium levels in packaged food products and industry meetings alone are not sufficient to lower average sodium levels in packaged foods in the absence of government leadership and measurable sodium targets.

Hypertension care during the COVID-19 pandemic in an integrated health care system

Retention in hypertension care, medication adherence, and blood pressure (BP) may have been affected by the COVID-19 pandemic. In a retrospective cohort study of 64 766 individuals with treated hypertension from an integrated health care system, we compared hypertension care during the year pre-COVID-19 (March 2019-February 2020) and the first year of COVID-19 (March 2020-February 2021). Retention in hypertension care was defined as receiving clinical BP measurements during COVID-19. Medication adherence was measured using prescription refills. Clinical care was assessed by in-person and virtual visits and changes in systolic and diastolic BP. The cohort had a mean age of 67.8 (12.2) years, 51.2% were women, and 73.5% were White. In 60 757 individuals with BP measurements pre-COVID-19, 16618 (27.4%) had no BP measurements during COVID-19. Medication adherence declined from 86.0% to 80.8% (p < .001). In-person primary care visits decreased from 2.7 (2.7) to 1.4 (1.9) per year, while virtual contacts increased from 9.5 (12.2) to 11.2 (14.2) per year (both p < .001). Among individuals with BP measurements, mean (SD) systolic BP was 126.5 mm Hg (11.8) pre-COVID-19 and 127.3 mm Hg (12.6) during COVID-19 (p = .14). Mean diastolic BP was 73.5 mm Hg (8.5) pre-COVID-19 and 73.5 mm Hg (8.7) during COVID-19 (p = .77). Even in this integrated health care system, many individuals did not receive clinical BP monitoring during COVID-19. Most individuals who remained in care maintained pre-COVID BP. Targeted outreach may be necessary to restore care continuity and hypertension control at the population level.

Law, Economics, and Privacy: Implications of Government Policies on Website and Third-Party Information Sharing

Widespread abuse of internet users' privacy online has prompted user advocacy groups to implore governments to intervene and protect consumer rights. To study such interventions' effects, we examine data-protection policies that policy makers and governments can enforce on websites, including consent-based user information sharing and subsidizing competing websites. Interestingly, we find that even though a consent-based policy may improve user surplus, it has the unintended consequence of increasing the number of third-parties and, thus, sharing of user information. We also determine that both consent-based and website subsidization policies may reduce competition by driving websites out of the market—to the detriment of user surplus and social welfare. Moreover, consent-based policies are not beneficial to websites, but are beneficial for third-parties. Policy makers should consider the different policy mechanisms at their disposal. Website subsidization is similar to a scalpel, enabling them to sculpt around and impact specific target markets. Consent-based policies are more comparable to a sledgehammer that uniformly affects all market segments. For circumstances where it is difficult for the government to enact a law for the entire market, website subsidization policies may be appealing alternatives, as they may yield higher user surplus than consent-based policies.

Elevated Anxious and Depressed Mood Relates to Future Executive Dysfunction in Older Adults: A Longitudinal Network Analysis of Psychopathology and Cognitive Functioning

Vulnerability models posit that executive-functioning (EF) problems centrally affect future common (vs. rare) psychopathology symptoms. Conversely, scar theory postulates that depression/anxiety (vs. other psychopathology) symptoms centrally influence reduced EF. However, most studies so far have been cross-sectional. We used cross-lagged panel network analysis to determine temporal and component-to-component relations on this topic. Community older adults participated across four time points. Cognitive tests and the caregiver-rated Neuropsychiatric Inventory assessed nine psychopathology and eight cognitive-functioning nodes. Nodes with the highest bridge expected influence cross-sectionally were agitation and episodic memory. Episodic memory had the strongest inverse relation with age. Agitation had the strongest negative association with global cognition. EF nodes tended to be centrally affected by prior depressed and anxious moods rather than influential on any future nodes. Heightened anxious and depressed mood (vs. other nodes) centrally predicted future decreased EF-related (vs. non-EF-related) nodes in older adults, supporting scar (vs. vulnerability) theory.

Current Practices in Missing Data Handling for Interrupted Time Series Studies Performed on Individual-Level Data: A Scoping Review in Health Research

Objective

Missing data can produce biased estimates in interrupted time series (ITS) analyses. We reviewed recent ITS investigations on health topics for determining 1) the data management strategies and statistical analysis performed, 2) how often missing data were considered and, if so, how they were evaluated, reported and handled.

Study Design and Setting

This was a scoping review following standard recommendations from the PRISMA Extension for Scoping Reviews. We included a random sample of all ITS studies that assessed any intervention relevant to health care (eg, policies or programmes) with individual-level data, published in 2019, with abstracts indexed on MEDLINE.

Results

From 732 studies identified, we finally reviewed 60. Reporting of missing data was rare. Data aggregation, statistical tools for modelling population-level data and complete case analyses were preferred, but these can lead to bias when data are missing at random. Seasonality and other time-dependent confounders were rarely accounted for and, when they were, missing data implications were typically ignored. Very few studies reflected on the consequences of missing data.

Conclusion

Handling and reporting of missing data in recent ITS studies performed for health research have many shortcomings compared with best practice.