Methodology

To augment existing literature with more diverse methodologies, Exemplars took a holistic approach than prior reviews of anemia reduction among women of reproductive age (WRA) in the Philippines, triangulating across literature reviews, quantitative analyses, and qualitative inquiry.

Literature review

Exemplars performed a systematic search of published peer-reviewed literature to gather information on contextual factors, interventions, policies, strategies, programs, and initiatives that may have affected anemia among WRA in the Philippines over time.

The epidemiology and etiology of anemia are multifactorial and involve a complex interplay of distal, intermediate, and proximal causes.^1,2,3 As part of the larger Exemplars in Anemia Reduction Among WRA project, Exemplars carried out a systematic review of peer-reviewed and gray literature on the determinants and drivers of anemia reduction among WRA in lower- and middle-income countries. Exemplars search identified several review articles, which was then used to create a conceptual framework to guide the analytical approach and assist in identifying and interpreting determinants of anemia among WRA.

Initial indexed literature database searches returned 3,507 records, which were reduced to 1,433 after de-duplication. Applying the screening criteria to titles and abstracts left 113 records, which were then reduced to 22 upon full-text review.

Quantitative analyses

Quantitative methods involved (1) descriptive analyses to provide contextual understanding of the decline of anemia across geographic, socioeconomic, gender, and age segments, and (2) hierarchical multivariable regression and regression-based decomposition analyses to understand the major predictors of the decline in anemia, as well as their relative importance to the Philippines' progress.

Since 2008, three rounds of Demographic and Health Surveys (DHS) have been conducted in the Philippines (2008, 2013, and 2018).^4,5,6 These were the primary quantitative data sets used in this study. The DHS are nationally representative household surveys. During each round, data for a wide range of indicators in the areas of population, health, and nutrition are collected, using a comparable standardized method.⁷ Anemia testing for WRA was included in each of the three rounds of Philippines DHS.

Determinants of anemia among WRA can be grouped in different hierarchical levels in terms of their causal proximity to the impact of interest—specifically, in "distal causes," "intermediate causes," and "proximal causes" (Figure 20). Each of these lies on a causal path toward nutritional outcomes, with more proximal causes functioning as mediators of the distal determinants.

Descriptive analyses

Exemplars created panel data sets from the 2008 and 2018 DHS to assess factors associated with hemoglobin (Hb) increase/anemia prevalence decrease during the study period. Given that Hb levels change throughout pregnancy due to hemodilution and an increase in blood volume, we restricted all multivariable analysis to non-pregnant women only.

The Anemia Exemplars conceptual framework (Figure 20) was used to select possible predictors of Hb and anemia (defined as Hb < 12 g/dL in non-pregnant women).⁸ Univariate statistics were estimated using means and standard deviations for continuous variables and frequencies/proportions for categorical variables, as appropriate. All analyses accounted for survey design and weighting, as appropriate.

Equity analyses were designed to illustrate subnational variations in anemia prevalence among WRA across household wealth, maternal education, area of residence, and geographic region. The slope index of inequality and concentration index were also calculated to measure absolute and relative socioeconomic inequalities, respectively.

Step 1 was a series of bivariate regressions to determine crude associations between indicators in our conceptual framework and Hb/anemia outcome. Step 2 was to use all candidate variables for multivariable model building (i.e., with p value ? .20) irrespective of their direction to move forward for multivariable modeling. Bivariate models estimated the absolute crude associations between the covariable and the outcome, and they highlighted the total (unadjusted) effect of the factor on Hb/anemia.

To examine the association between Hb and various indicators, Exemplars conducted a series of hierarchical models using distal-, intermediate-, and proximal-level variables to generate the final multivariable models. Variables within each level were selected from the general conceptual framework. The final multivariable regression coefficient was adjusted for child age, sex, and region (control variables) and all confounders in preceding levels.

Oaxaca-Blinder decomposition

Exemplars only included the survey years of 2008 and 2018 by design, since the Oaxaca-Blinder decomposition only uses two survey time points in a given analysis and thus "ignores" in-between survey rounds and any intermittent fluctuations in the predictors. Exemplars research operationalized Hb as the linear outcome due to its greater statistical efficiency relative to the dichotomous anemia outcome.

Exemplars undertook the commonly used Oaxaca-Blinder decomposition methods to assess determinants of change in anemia prevalence among WRA in the Philippines over time.⁹ These methods, which are based on individual-level data, have increased statistical power and have been widely used to assess nutrition determinants over time in low- and middle-income settings.^10,11,12,13

Qualitative analysis

The qualitative element of the study was conducted at the national, district, and community levels to investigate a diverse range of stakeholder perspectives. The qualitative study was conducted at the national level, as well as subnational levels in selected provinces and cities on the island of Luzon in the Philippines. At the local level, the province of Nueva Vizcaya and city of Caloocan were identified as high-performing areas, whereas the province of Benguet and city of Makati were identified as low-performing areas.

At the national level, a total of 45 informants were interviewed for the study, selected on the basis of their experience in areas or institutions that were instrumental in the design and implementation of interventions to reduce anemia among WRA in the Philippines. The national interviews involved key government ministries, departments, and agencies; global development partners (World Food Programme, United Nations Children's Fund [UNICEF], international nongovernmental organizations); local nongovernmental organizations; academia; medical organizations; and industry experts.

At the subnational level, interviews were conducted with 11 stakeholders. Subnational stakeholders primarily consisted of municipal and provincial health officials, health care workers with at least five years' experience delivering maternal health and nutrition services in the community, and community members or opinion leaders who influenced the uptake of maternal health and nutrition services among WRA in the community.

At the community level, 32 focus group discussions (FGDs) with five to seven participants from each of the different groups of WRA and community experts across the four study areas (Nueva Vizcaya, Benguet, Caloocan City, and Makati City) were conducted. An equal number of FGDs were conducted between high- and low-performing areas, with the following total coverage across categories: eight FGDs among community experts, eight FGDs among non-pregnant/nonlactating women ages 15 to 30 years, eight FGDs among WRA ages 31 to 49 years, four FGDs for pregnant women, and four FGDs for lactating mothers.

Program, policy, and financing review

To understand the implementation of nutrition-sensitive and nutrition-specific policies, programs, and strategies, Exemplars conducted additional research and corroborated our findings with country experts. A similar multipronged data collection and corroboration exercise was undertaken to track financial data linked to the nutrition policy and program timeline.

Limitations

The main strength of the Exemplars study was the mixed-methods approach, which contextualized the quantitative findings and situated them within a framework that clearly demonstrated how the Philippines was able to achieve a reduction in anemia burden between 2008 and 2018. However, Exemplars analysis had limitations as well. The main data source for our analysis was the Philippines DHS, which are cross-sectional surveys conducted approximately every five years. Therefore, causality could not be inferred. However, Exemplars used data from two survey years to create a panel data set, which enabled assessment of the effect of changes in anemia determinants on anemia among WRA over time. Additionally, Exemplars multivariate statistical analysis also controlled for time-invariant region of residence, which accounted for any trend effects. Additionally, as previously established, the etiology of anemia is complex and multifactorial, including nutrient deficiencies, infection, inflammation, and hemoglobinopathies; quantitative data on these, specifically dietary intake and iron deficiency, were not available. Finally, although qualitative inquiry was used to address some of the gaps in quantitative data, Exemplars only carried out subnational and community-level data collection in two regions and districts, respectively. Therefore, Exemplars findings are not generalizable nationally.