Table 1
Social marketing benchmark criteria.
| SCORECARD ELEMENT # | CRITERIA | DEFINITION |
|---|---|---|
| 1 | Behavioral focus | The study aims to change behavior |
| 2 | Segmentation | The intervention addressed a specific population group and provided a rationale for the targeting/selection strategy |
| 3 | Formative research | Research on the priority population was conducted prior to the definition of the intervention |
| 4 | Exchange | The intervention creates motivational exchanges that are attractive to the priority population |
| 5 | Competition | There is consideration of competing behaviors that the priority population may be inclined to adopt |
| 6 | Marketing mix | Use of at least one of the 4Ps derived from marketing strategy |
| 7 | Community-involvement | Community plays a role in the design, implementation, and evaluation of the program |
| 8 | Integration | The intervention is positioned within broader policy-program efforts that address the specific public health issue, and the design takes into consideration stakeholders’ activities |
Figure 1
Study selection PRISMA diagram.
Table 2
Summary of behavior change (study effectiveness) findings by study.
| STUDY | BEHAVIOR | BEHAVIOR CHANGE (STUDY EFFECTIVENESS) |
|---|---|---|
| An et al. (107) | Healthy food purchase among participants in one insurance program | 2/3 of the difference in healthy food purchase between participants and non-participants was attributable to the program. Consumption of foods high in salt decreased by more than 20% |
| Anderson et al. (68) | Reduction in sodium intake through emphasis on spices and herbs | Mean 24-h urinary sodium excretion was significantly lower in the intervention group |
| Beer-Borst (39) | Reduction in sodium intake through workplace meal purchase intervention | The overall mean change in daily salt intake was –0.6 g (from 8.7 to 8.1 g, or 6.9%). Though the mean daily salt intake of women (7 g) was unaltered, the mean intake of men declined by –1.2 g (from 10.4 to 9.2 g). Baseline salt intake, sex, and waist-to-height ratio were significant predictors of salt reduction. The analysis also highlighted key determinants of low adoption and reach and effective program implementation in catering operations. |
| Bernabe-Ortiz et al. (105) | Promotion of a low sodium salt substitute by replacement with 25%KCl/75%NaCl at community and individual level (vendors, businesses, kitchens, bakeries, restaurants, and homes) | Of 2376 participants, an average reduction of 1.29 mmHg [95% confidence interval (95% CI) (–2.17, –0.41)] in systolic and 0.76 mmHg [95% CI (–1.39, –0.13)] in diastolic blood pressure. Participants without hypertension at baseline, in the time- and cluster-adjusted model – 51% [95% CI (29%, 66%)] reduced risk of developing hypertension compared with the control group. In 24-h urine samples: no difference in NA levels, mean difference 0.01; 95% CI (0.25, –0.23); K levels higher, mean difference 0.63; 95% CI (0.78, 0.47). |
| Bin Sunaid (40) | Reduction in sodium intake through government regulation, a marketing campaign, and educational materials in strategic locations such as restaurants and workplaces | Government compliance was moderate. Only 2% of manufacturers adopted front-of-pack nutrition labels. Data collected on 363 establishments revealed that 27% did not display caloric content, 25% had incomplete displays of caloric content, and 19% featured incorrect calculations. Of the 297 products assessed, 85% were compliant with the advised sodium limit of 1%; however, 25%–50% of pastries prepared with meat, hamburgers, and all processed meats were non-compliant with the government sodium recommendations. |
| Bouterakos (38) | Provision of salt-reduced meals in schools, and digital education of children to limit salt in the home | A total of 28 interviews were completed with 13 children, 11 parents, 3 principals, and 1 teacher. Children and adults self-reported dietary change and reduction of sodium intake. Participating children also showed improvements in self-reported salt-related knowledge and self-efficacy, and fewer children reported placing a salt shaker on the table. |
| Brown et al. (69) | Reduction in sodium intake | Church members in the intervention group showed a greater increase in fruit and vegetable intake than the control group [0.25 cups per day (95% confidence interval: 0.08, 0.42), P = 0.002], a greater decrease in sodium intake [–123.17 mg/day (–194.76, –51.59), P = 0.04], but no difference in moderate- or greater-intensity physical activity [–27 metabolic-equivalent minutes per week (–526, 471), P = 0.56]. |
| Cateriano (28) | Understanding salt-related behaviors and salt use during cooking by observation through a journey-mapping process | In three stages of food shopping and cooking, 13 salt touchpoints were observed, with the highest number occurring during food preparation. No shopping lists were made, and though artificial ingredients containing salt were included in purchases, a variety of natural seasonings and spices were also purchased to enhance flavor. All participants tasted the food during preparation and flavored it with natural spices and herbs as well as salt. None of the participants put a salt shaker on the table at the time of serving the meal. Therefore, natural ingredients in cooking can be an opportunity to replace salt in the diet. |
| Cappuccio et al. (108) | Reduction in salt intake through community-based health-promotion intervention. The intervention included a health education program carried out by community health workers, with daily sessions for the first week and once weekly afterwards | There was no significant change in urinary sodium between groups, while the intervention group showed lower systolic and diastolic blood pressure |
| Chen et al. (94) | Reduction in salt intake | Participants in the intervention group (salt restriction spoon and health education) significantly decreased their salt consumption compared to the control group. Before the intervention, 26.1% of intervention group participants reported often or daily use of a salt-restriction-spoon, and 13.3% reported using it correctly. After the intervention, 67.3% of intervention group participants reported often or daily use of the spoon, and 37.3% reported correct use. This significantly higher use rate and correct use resulted in a daily salt reduction of 1.42 g, and a 24HUNa reduction of 34.84 mmol. |
| Chu et al. (135) | Reduction in sodium intake, measurement of effectiveness of a national population-level program | Health education activity attendance was 61.5% for general villagers and 92.3% for people with high risk of cardiovascular disease. The 18-month (n = 1903) 24-h mean urinary sodium excretion in the intervention arm was reduced by 5.5% (–14 mmol/day, 95% confidence interval –26 to –1; P = 0.03), while potassium excretion increased by 16% (+7 mmol/day, +4 to +10; P < 0.001), and the sodium to potassium ratio declined by 15% (–0.9, –1.2 to –0.5; P < 0.001). |
| Cornelio et al. (37) | Reduction in salt use during cooking through intervention aimed at improving self-efficacy and promoting behavior change | At 3-month follow-up, the intervention group improved significantly more than the control group regarding salt addition measures (P-values between 0.05 and 0.001) and psychosocial variables (all P-values ≤0.001). The reduction in 24-h urinary sodium excretion was not significant. |
| Cotter et al. (89) | A comparison of the effect of salt reduction education (THEOR) and a combination of education and practical gardening and cooking lessons (PRACT). | The group subjected to salt reduction education and practical activities saw a significant reduction in salt intake. At baseline, 139 students (76 girls and 63 boys) were eligible for the study, and showed an average 24-h UNa of 132 ± 43 mmol/24 h (mean salt intake of 7.8 ± 2.5 g/day) and a BP of 118/62 (13/9) mmHg. At the end of the study, BP decreased by 8.2/6.5 mmHg versus baseline in the control group (n = 31), by 3.8/0.6 mmHg in THEOR group (n = 43) and by 3.5/0.7 mmHg in the PRACT group (n = 53). Salt intake was reduced by 0.4 ± 2.4 g/day among the control group, by 0.6 ± 3.2 g/day in the THEOR group and by 1.1 ± 2.5 g/day in the PRACT group. Variation in salt intake was dependent on the group (χ, 9.982, P = 0.041). Salt intake was only significantly reduced in the PRACT group (1.1 g/day), and the percentage of children in this group who reduced salt intake by at least 1 g/day from baseline was significantly higher (50.9%) than in the other groups, (THEOR, 48.8% and CTR, 32.2%). |
| Cummings et al. (70) | Integration in sodium reduction strategies in food procurement and vending food venues | Three government departments adopted the new nutrition standards and requirements (including sodium limits and best practices such as the use of signage, pricing incentives and menu labeling), potentially affecting 100,000 meals sold daily in government venues. |
| Daivadanam (103) | Change in household dietary habits including reduction in sodium intake through procurement of fruits and vegetables (FV), substitution of fried foods with steamed or fruit snacks, changing the color of the food on the plate by increasing vegetables, increasing the display/accessibility of FV in homes a and decreasing the display of jams/pickles/fried snacks, buying local FV, and reallocating budgets to purchase more FV | Monthly household consumption of salt was reduced by 45% in the intervention arm compared to the control arm |
| Do et al. (100) | Reduction in salt intake intervention based on the COMBI framework. Activities included: mass media communication, communication in schools, community-level program and home visits. | Mean urinary sodium excretion fell significantly in the communities where the program was implemented. Mean sodium excretion in spot urine sampling fell significantly from 8.48 g/day at baseline to 8.05 g/day at follow-up (P = 0.001) |
| Eyles (87) | Improve cardiovascular health through lower salt food purchases mediated by the use of an app | A significant reduction in mean household purchases of salt (~0.7 g of salt per person per day) was noted during the 4-week intervention phase. |
| Fitzgerald (91) | Improve diet habits including salt reduction in the workplace through cafeteria catering and nutrition education for participants and catering staff in way that is cost effective for management. Interventions included menu modification, increase in fiber, price discounts, strategic positioning of food, and portion size control, individual nutrition consultants, and detailed nutrition information | This complex workplace dietary intervention combining nutrition education and system-level dietary modifications reduced employees’ intake of salt and saturated fat (significant reductions in on-duty intakes of total fat (–14.2 g/day, p ¼ 0.000), saturated fat (–7 g/day, p ¼ 0.000), salt (–1.4 g/day, p ¼ 0.000) and total sugars (–8.9 g/day, p ¼ 0.003), improved employees’ nutrition knowledge and decreased their body mass index in a cost effective way. The system-level and combined interventions had positive net benefits; the savings gained from reduced absenteeism were greater than the costs of the intervention. The system-level intervention had the highest net benefit: $53.56 per employee. |
| Fitzgerald (92) | Improved dietary habits at work, including salt reduction, extending to the employees’ off-duty eating habits through nutrition education (Education), environmental dietary modification (Environment), or both (Combined). | Improvements observed in employees’ dietary intakes at work also extended to their lives outside of work. Significant reductions in on-duty intakes of total fat (–14.2 g/day, p ¼ 0.000), saturated fat (–7 g/day, p ¼ 0.000), salt (–1.4 g/day, p ¼ 0.000) and total sugars (–8.9 g/day, p ¼ 0.003) were observed in the Combined and Environment groups [total fat (–11.4 g/day, p ¼ 0.017) and saturated fat (–8.8 g/day, p ¼ 0.000)]. In the Combined group, significant changes were also observed in off-duty intakes of total fat (–10.0 g/day, p ¼ 0.001), saturated fat (–4.2 g/day, p ¼ 0.001), salt (–0.7 g/day, p ¼ 0.020), and total sugars (–8.1 g/day, p ¼ 0.020). |
| Francis et al. (71) | Dietary habits including salt intake | The intervention group that received two dietitian-led education sessions at home consumed significantly less sodium than controls. |
| Fujiwara et al. (95) | Salt reduction to decrease urine albumin-creatinine ratio among albuminuria patients | Participants in the intervention group (those receiving family and community support to motivate behavior change) showed a significant reduction in albumin-creatinine ratio (ACR) from baseline. The intervention group had a lower ACR compared to the control group, although P = 0.007. |
| Gans et al. (113) | Teaching healthy salt and fat reduction techniques during cooking as part of a cook-off contest for home economics classes embedded in a wider healthy heart initiative | 42 students with elevated blood cholesterol levels were invited to return for follow-up; 40 students (95%) returned. Mean change in blood cholesterol level from baseline to follow-up was 21.7 mg/dL (P < 0.0001). When expressed as a percentage of baseline, this represented a 10.7% average reduction in blood cholesterol (P < 0.0001). |
| Gonzales (86) | Adoption of national salt reduction strategy through the removal of access to sodium in restaurants, food service establishments and vendors | 47 restaurants removed salt shakers, soy sauce, and finadene from their tables and establishments. At least 500 salt-reduction trifolds were distributed to participating restaurants, and 2000 additional pamphlets were made available for replenishing purposes during project monitoring to ensure sustainability. |
| Grimes (84) | Reduction in sodium intake through a consumer awareness campaign, and before and after surveys of parents/caregivers with children nationwide | There were limited changes in self-reported knowledge, attitudes, and behaviors among adults in this study. The strongest evidence of improvement related to the behaviors of children as reported by adults. The percentage of parents/caregivers who agreed that limiting salt in their child’s diet was important increased by 8% (P = 0.001), and this coincided with a 10% reduction in table-placed saltshakers, and a 9% reduction in salt added by children at the table (both P < 0.001). |
| Grunseit (81) | Reducing consumption of unhealthy takeaway foods, including those high in salt, through peer support therapy | Participants self-reported a reduced consumption of takeaway food by participating in four main activities: recasting reduction as saving money, making small changes, engaging in self-care, or goal-setting; adding practical changes to behavior in the way of planning, rule-making, or portion-adjustment; using external instruments such as the food environment and social support; and reconfiguring social events. |
| Ireland et al. (82) | Reduction in sodium intake | Participants receiving dietary education about choosing foods identified by a Tick symbol or Food Standards Australia and New Zealand’s low-salt guideline of 120 mg sodium/100 g food saw a significant reduction in urinary sodium excretion. Reported sodium intake (multiple-pass 24-h recall) significantly decreased only for the Food Standards group. |
| Johnston et al. (72) | Adoption of marketing strategies, taste demonstrations and media campaign by local grocery stores | Not reported |
| Jordan (76) | Salt reduction through meal procurement, cafeteria, restaurant and catering programs | Sodium content of targeted foods or meals decreased by 261 mg (from 946 mg at baseline to 685 mg at final follow-up) in the 12 food service settings that submitted data. |
| Kim (99) | Salt reduction through use of a mobile health app to encourage behavioral changes in individuals with metabolic disorders | Preference for a low-sodium diet, reading nutritional facts, having breakfast, and performing moderate physical activity significantly increased in the mHealth intervention group (IG) (app users) as compared to the conventional (CG) health center users. At baseline, the practice of reading nutritional facts was significantly lower in IG (15.81%) than in CG (25.73%) (P = 0.0007) after 24 weeks it was significantly higher in for IG (46.10%) as compared to CG (28.64%, P < 0.0001). Within each group, low salt preference and label-reading significantly rose in IG over 24 weeks (P < 0.0001 and P = 0.0006, respectively), with no significant change in CG. |
| Klassen (77) | Awareness of the link between dietary sodium, hypertension and stroke among a hard-to-reach priority population (20- to 40-year-old Black males) through public education campaigns and street intercept surveys | 30% of post-campaign respondents reported familiarity with key campaign content compared to only 17% of pre-campaign respondents; 17% post-campaign respondents provided accurate recall; 41% recalled stroke relationship to salt. Those respondents who remembered the key phrase ‘Mom Says’ in one of the campaigns were 95% more likely to remember the connection between salt and stroke. |
| Land et al. (83) | Reduction in salt intake | Mean salt intake (measured through 24-h urinary excretion) significantly decreased, while knowledge of recommendations about salt reduction and strategies to reduce salt improved following implementation of a multi-faceted community-based program. However, the proportion of people who checked food labels and avoided processed food decreased. Overall, a 10% reduction in salt consumption was observed in the community. |
| Layeghiasl (29) | Reduction of salt intake in 25- to 50-year-olds | A social marketing program featuring educational materials, classes, phone counseling, and brief interventions by health personnel produced a significant reduction in salt intake (3.01 ± 2.38 g/day), and a significant change in knowledge (mean ± standard deviation of change = 2.58 ± 1.3, P = 0.001), attitude (mean ± standard deviation of change = 1.68 ± 4.03, P = 0.001) and practices (mean ± standard deviation of change = 3.37 ± 2.92, P = 0.001) in the intervention group, while this did not change in the control group. |
| Lee Kwan et al. (74) | Customer reach of Baltimore Healthy Carry-outs and purchase of healthier products | Intervention included improvements to menu boards and labeling to promote healthier items, introduction of healthier sides and beverages as well as affordable healthier combo meals. Purchases of healthier foods increased by almost 40% compared to baseline at intervention carry-outs. |
| Livingston et al. (93) | Reduce intake of discretionary foods through personalized (phenotypic and genotypic) nutrition advice | Three levels of intervention produced different results: for L1 (diet and physical activity), L2 (diet and activity+ personalized phenotypic feedback based on nutrient and metabolic biomarkers), and L3 (diet and activity + phenotypic + genotypic feedback based on variants in nutrient-responsive genes). L2 and L3 randomizations resulted in greater reductions in the percentage of energy, total fat, saturated fat, and salt consumed through discretionary foods, with a 0.48 ± 0.17 difference in salt intake between the control group and the intervention group. |
| Long (78) | Salt reduction through community meals program | Across three programs, the mean amount of sodium served per diner from baseline to Year 1 follow-up decreased from 1443 to 864 mg (–40%). The mean amount of sodium served per diner in Year 2 was 920 mg, which was more than the 864 mg observed in Year 1 (+6%) but less than baseline (–36%). At the Year 3 follow-up, the mean amount of sodium served per diner was 944 mg, which was more than Year 2 but less than baseline (–35%) |
| Ma (79) | Promote physical activity and reduce dietary sodium intake | An educational intervention culturally tailored to Filipino Americans produced a non-statistically significant decrease in urine sodium, a blood pressure reduction of 12.6 mmHg, and diastolic pressure decrease of 3.8 mmHg in the intervention group |
| Ma (102) | Reduce salt intake in children through social group association | Salt reduction score (SRB) = Answer to three questions on questionnaire: (1) high-salt snack frequency; (2) high-salt pickle frequency; (3) family salt reduction (y/n). A 1-unit increase in SRB was associated with a 0.31 g/day greater reduction in salt intake during the trial (95% CI 0.06 to 0.57, P = 0.016). The more family members a child had who did not support salt reduction, the lower the SRB. Children with more friends had higher SRB scores (all p < 0.05). Children whose teachers attended the intervention had higher SRB scores (P = 0.043) |
| Nader (73) | Reduction in salt intake through year-long family-focused intervention | Anglo-American families in the study reported a lower sodium intake than Mexican-American families. Overall, the 3-day salt score significantly decreased in both groups. |
| Perlmutter (75) | Acceptability of low sodium entrees in a workplace cafeteria | No significant difference in sales was observed after the introduction of modified entrees, and no significant changes were observed in overall acceptability. When entrees were advertised as lower in fat and sodium, consumers reported higher acceptability. |
| Ponce-Lucero (106) | Identification of population-level salt reduction social marketing campaign audience | The study conducted formative research to inform the development of an intervention |
| Savedra et al. (104) | Sales of lower sodium breads | Introduction of lower sodium breads did not change sales, and bread samples prepared with less sodium were not discernible from regular bread |
| Sakaguchi (98) | Sodium reduction through a one-year work-related healthy lunch and nutrition education program | A significant decrease in urine sodium (a –4.6 g change from 14.2 to 9.6 g; 95% CI: –7.1, –2.1) was observed in the workers who consumed healthy lunches, compared to no significant change in the group that did not consume healthy lunches. The difference between the intervention and control groups was not significant. |
| Sosa (80) | Sodium reduction through a work-related cafeteria and congregate meal programs | All worksites improved on five out of seven sodium practices. At follow-up, when compared to baseline, more worksites reported using recipes (75% vs. 50%), measuring salt while cooking (100% vs. 75%), and reducing salt by offering smaller portion sizes (88% vs. 75%). For congregate meal programs, six out of seven sodium practices stayed the same from baseline to follow-up. |
| Talaei et al. (110) | Adoption of modified (lower sodium, higher in fiber) recipes for bread by bakeries (healthy bread) | Number of bakeries producing HB increased from 1 to 402 (41% of bakeries in intervention area) after 6 years. People who lived in the intervention area consumed significantly more whole grain bread than people in a control city. |
| Trieu (88) | Reduction in salt intake through awareness campaigns, community mobilization, and policy/environmental changes | The outcome evaluation found that while there were significant improvements in knowledge and self-reported behavior (intermediate outcomes), there were no changes in mean salt intake (7.3 g/day in 2013 vs. 7.5 g/day in 2015; P = 0.588) |
| van’t Riet et al. (90) | Reduction in salt intake following messaging promoting a low-salt diet | Overall there was no difference between participants based on self-efficacy level or frame of messaging received (gain vs. loss-framed messaging). For participants in the high self-efficacy condition, loss-framed messages were more effective than gain-framed ones in influencing participants’ intention to reduce salt intake. |
| Vaughn (27) | Improve diet (including reduced salt intake) and increase physical activity through childcare-based intervention | No significant changes were noted in any of the outcome measures except for small improvements in children’s sodium reduction (mean change = 0.52, P = 0.029). |
| Webster (85) | Reduce salt intake nationwide through voluntary food industry salt reduction, strategic health communication, and a hospital meals program | The evaluation showed a 1.4 g/day drop in salt intake from the 11.7 g/day at baseline, however this change was not statistically significant. |
| Wentzel (109) | Reduce population-level discretionary salt intake through a mass media campaign | Most of the indicators of knowledge, attitudes, and behavior change showed a significant move toward considering or initiating reduced salt consumption. Post-intervention, significantly more participants took steps to control salt intake (38% increased to 59.5%, P < 0.0001) by avoiding adding salt during cooking and at the table. |
| Wong (101) | Lifestyle intervention including the reduction of salt intake | Significant improvements in moderate-intensity physical activity (PA), vigorous-intensity PA, and total PA (P < 0.001), increased intake frequency of fruit and vegetables (P = 0.049), a reduction in salt and sugary beverage intake (P ≤ 0.042), and reductions in systolic blood pressure (BP; –3.68 mmHg), diastolic BP (–3.54 mmHg), and percentage body fat (–2.13%; P ≤ 0.020) when compared with the control group. |
| Yang, 2021 (97) | Reduce salt intake through social media campaign | Post-intervention, the salt-related knowledge score was relatively lower, while the salt reduction behavior score and high-salt intake behavior score were relatively higher. The percentage of participants who used salt measuring spoons, asked restaurants to use less salt, read the sodium content of foods, chose foods with low sodium content, and regularly used low-sodium salt increased significantly post-intervention (all P-values <0.05). |
Figure 2
Location of studies 1989–2021.
Figure 3
Marketing mix: product, price, place, and promotion strategies.
Table 3
Social marketing benchmark criteria checklist for included studies.
| STUDY | YEAR | BEHAVIORAL FOCUS | SEGMENTATION | FORMATIVE RESEARCH | EXCHANGE | COMPETITION | MARKETING MIX | COMMUNITY INVOLVEMENT | INTEGRATION |
|---|---|---|---|---|---|---|---|---|---|
| Nader et al. | 1989 | ||||||||
| Gans et al. | 1990 | ||||||||
| Perlmutter et al. | 1997 | ||||||||
| Cappuccio et al. | 2006 | ||||||||
| Francis et al. | 2009 | ||||||||
| Fujiwara et al. | 2010 | ||||||||
| Ireland et al. | 2010 | ||||||||
| van‘t Riet et al. | 2010 | ||||||||
| Chen et al. | 2013 | ||||||||
| Cotter et al. | 2013 | ||||||||
| Lee Kwan et al. | 2013 | ||||||||
| Talaei et al. | 2013 | ||||||||
| Cummings et al. | 2014 | ||||||||
| Johnston et al. | 2014 | ||||||||
| Anderson et al. | 2015 | ||||||||
| Brown et al. | 2015 | ||||||||
| Saavedra et al. | 2015 | ||||||||
| Cornelio et al. | 2016 | ||||||||
| Do et al. | 2016 | ||||||||
| Land et al. | 2016 | ||||||||
| An et al. | 2017 | ||||||||
| Eyles et al. | 2017 | ||||||||
| Wentzel et al. | 2017 | ||||||||
| Daivadanam et al. | 2018 | ||||||||
| Fitzgerald et al. | 2018 | ||||||||
| Trieu et al. | 2018 | ||||||||
| Webster et al. | 2018 | ||||||||
| Beer-Borst et al. | 2019 | ||||||||
| Grunseit et al. | 2019 | ||||||||
| Kim et al. | 2019 | ||||||||
| Ma et al. | 2019 | ||||||||
| Sosa et al. | 2019 | ||||||||
| Gonzales et al. | 2020 | ||||||||
| Ponce-Lucero et al. | 2020 | ||||||||
| Klassen et al. | 2020 | ||||||||
| Bouterakos et al. | 2020 | ||||||||
| Fitzgerald et al. | 2020 | ||||||||
| Grimes et al. | 2020 | ||||||||
| Jordon et al. | 2020 | ||||||||
| Layeghiasl et al. | 2020 | ||||||||
| Bernabe-Ortizet al. | 2020 | ||||||||
| Yang et al. | 2021 | ||||||||
| Bin Sunaidet al. | 2021 | ||||||||
| Livingstone et al. | 2021 | ||||||||
| Cateriano et al. | 2021 | ||||||||
| Sakaguchi et al. | 2021 | ||||||||
| Vaughn et al. | 2021 | ||||||||
| Chu et al. | 2021 | ||||||||
| Longet al. | 2021 | ||||||||
| Ma et al. | 2021 | ||||||||
| Wong et al. | 2021 |
[i] Grey: identified or partially identified; White: missing or not explicitly reported.