The study, published in PLOS Mental Health by Gallen Mlenge, Odass Bilame, and Lutengano Mwinuka, draws on the fifth wave of the Tanzania National Panel Survey, conducted in 2020 and 2021. The panel survey is a household-based instrument designed to be representative of the national population, which makes it a rare and valuable window into health behaviour in a low-income setting where routine administrative data on care-seeking is often incomplete. From the survey, the researchers analysed a sample of 11,891 individuals aged 15 years and above who had non-missing outcome data, making it one of the largest attempts to characterise healthcare utilisation patterns in the Tanzanian population.

One of the central methodological challenges the authors faced is familiar to anyone working on mental health in low- and middle-income countries: population surveys rarely include clinical diagnostic instruments. Instead, the team used a proxy measure. Mental health need was identified through the Washington Group Short Set item on difficulty remembering or concentrating, applied at the severe threshold. This item is a recognised proxy associated with common mental disorders, and while it cannot substitute for a clinical interview, it provides a consistent, internationally comparable indicator that can be embedded in large multipurpose surveys. Using this definition, 54 individuals in the sample were classified as having proxy-identified mental health need, corresponding to a weighted prevalence of 0.45 percent of the adult population.

The outcome measure was deliberately broad. The researchers counted any visit to a formal provider in the four weeks preceding the interview, regardless of the reason for the visit. This captures the overall propensity to engage with the formal health system rather than care-seeking for a specific condition. Overall, weighted formal healthcare utilisation stood at just 19.2 percent, meaning that fewer than one in five Tanzanians aged 15 and above had contacted a formal provider in the previous month. In a country where the burden of disease includes both communicable and increasingly non-communicable conditions, that figure underscores how much of the population remains outside the reach of routine formal care.

To explain who used care and who did not, the authors turned to the Andersen Behavioural Model, a long-standing framework in health services research that organises determinants of utilisation into predisposing characteristics, enabling resources, and need factors. They estimated survey-weighted logistic regressions producing adjusted odds ratios and predicted probabilities. The results revealed a system that sorts people by demography and geography rather than by need. Female sex, older age, specifically 55 years and above, and residence in the Southern Highlands zone were each independently associated with higher utilisation, suggesting that both biological and structural factors shape contact with the health system.

The most striking finding, however, concerned household wealth. Utilisation rose in a strong dose-response gradient across wealth quintiles: the richer the household, the more likely its members were to have visited a formal provider. Individuals in the richest quintile had 2.71 times higher adjusted odds of utilisation compared with those in the poorest quintile. In other words, the ability to pay, and the enabling resources that come with it, such as transport, proximity to facilities, and the capacity to absorb the indirect costs of seeking care, appear to be among the dominant gatekeepers to formal healthcare in Tanzania. This gradient is a direct challenge to the principle of equitable access that underpins universal health coverage ambitions.

Against this backdrop, the finding on mental health need is quietly devastating. Proxy-identified mental health need was not significantly associated with formal healthcare utilisation. The adjusted odds ratio was 1.27, with a 95 percent confidence interval spanning 0.53 to 3.04 and a p-value of 0.588. While the point estimate leans in the direction of slightly higher utilisation among those with identified need, the interval is wide and crosses unity, meaning the data cannot distinguish the effect from no effect at all. People whose survey responses signalled severe difficulty remembering or concentrating were, statistically, no more likely to have seen a formal provider in the previous month than anyone else.

The authors were careful about the limits of that subgroup. Only 54 individuals carried the proxy-identified need flag, and missing outcome data affected 505 individuals in a pattern classified as Missing Not At Random, meaning that whether someone’s outcome was missing was related to the outcome itself. To probe how fragile the subgroup estimates might be, the team conducted an extreme bounds sensitivity analysis. The result was a stark illustration of statistical uncertainty: true utilisation in the subgroup could plausibly range from 2.0 percent to 92.7 percent. The authors therefore describe their findings for the mental health need subgroup as exploratory, a candid caveat that is rare and welcome in this literature.

That honesty matters, because the temptation in global mental health research is often to overread thin data. Here, the study does two things at once. It establishes with reasonable confidence the broad structural determinants of care-seeking in Tanzania, since the full sample of nearly 12,000 people provides substantial statistical power for the wealth, sex, age, and zone effects. At the same time, it demonstrates precisely why mental health need remains nearly invisible in household survey data: the affected group is small, the proxy is coarse, and the missingness is informative. The study is as much a methodological lesson as a substantive one, showing what national panels can and cannot reveal about the health-seeking behaviour of people with mental health conditions.

The policy implications, nonetheless, point in a clear direction. If wealth is the strongest predictor of who reaches a doctor, then removing financial barriers, through mechanisms such as fee exemptions, insurance expansion, or support for indirect costs, should sit at the centre of efforts to make healthcare utilisation more equitable in Tanzania. And if residents of some geographic zones systematically lag behind, then strengthening service availability in lower-utilisation regions becomes an equally urgent priority. For the mental health community specifically, the study suggests that integrating mental health need into general health system planning will require better measurement, larger samples, and data systems that do not lose the very people whose outcomes are hardest to capture. Until then, the quiet finding that mental health need does not move the needle on care-seeking in Tanzania stands as both a data point and a warning about how much the health system, and the surveys that measure it, still miss.

Subject of Research: Determinants of formal healthcare utilisation among adults with and without proxy-identified mental health need in Tanzania

Article Title: Patterns and determinants of formal healthcare utilisation among individuals with and without proxy-identified mental health need in Tanzania: A cross-sectional analysis of the National Panel Survey

Article References: Mlenge, G., Bilame, O., & Mwinuka, L. (2026). Patterns and determinants of formal healthcare utilisation among individuals with and without proxy-identified mental health need in Tanzania: A cross-sectional analysis of the National Panel Survey. PLOS Mental Health, 3(9), e0000644. https://doi.org/10.1371/journal.pmen.0000644

Image Credits: AI Generated

DOI: 10.1371/journal.pmen.0000644

Keywords: Tanzania, healthcare utilisation, mental health, health equity, household wealth, National Panel Survey, Washington Group Short Set, Andersen Behavioural Model, low- and middle-income countries, cross-sectional analysis, health policy, survey methods

Garston Liang of the University of Technology Sydney, together with Mackenzie Glover and Guy E. Hawkins of the University of Newcastle, compared two widely used methods of preference elicitation: ranking and best–worst scaling, often abbreviated as BWS. In a ranking task, respondents order a full list of items from most to least preferred, a format familiar from hiring panels, consumer surveys, and even Australia’s preferential voting system. In best–worst scaling, by contrast, respondents see only small subsets of items at a time and simply pick the one they favor most and the one they favor least. Across three experiments involving hundreds of participants, the team found that both methods largely agree on the ordering of preferences, but that BWS delivers markedly better test–retest reliability—meaning people’s answers stay more consistent when measured repeatedly, even over intervals as short as a few minutes.

The theoretical stakes of this comparison are considerable. One long-standing view in psychology and behavioral economics assumes that people hold stable internal representations of their preferences, which measurement merely reveals, with any variability attributable to the tool being used. A competing perspective, known as the constructed preferences view, holds that preferences are assembled on the spot, packaged with the conditions of the moment—the available options, the framing of the question, even the mood of the respondent. Under that view, elicited preferences need not be coherent over time at all. Both perspectives agree, however, that the choice of elicitation method matters enormously, which makes the question of whether ranking and BWS actually measure the same thing a critical one for anyone designing surveys.

Each method carries distinct strengths and weaknesses. Ranking is quick, intuitive, and computationally cheap, and it works well when only a handful of options are involved. But its demands grow brutally with set size: ordering a top-ten list requires the equivalent of 45 pairwise comparisons, and marketing researchers routinely confront sets of dozens of competing products. Rankings also force respondents to discriminate between options they may genuinely feel indifferent about, manufacturing distinctions where none exist. BWS sidesteps both problems. Because people are naturally good at identifying what they love and what they loathe, asking for best and worst choices within small subsets keeps cognitive load low regardless of how many items are in play. Over repeated, carefully balanced choice sets, preferences for every item accumulate incrementally, and each choice constrains the possible orderings of items not even shown in that round.

To compare the two methods fairly, the researchers needed a domain where true preferences are unlikely to shift during the experiment. They settled on life values, using a validated set of ten values drawn from Schwartz’s Value Theory—concepts such as benevolence, hedonism, power, security, and self-direction. Fundamental changes in personal values unfold over years, dwarfing the minutes required for a survey, so any inconsistency observed between two measurements could be attributed to the measurement process itself rather than to genuine change in what people believe. The team also manipulated how the values were labeled: some participants saw broad dimension labels like “benevolence,” while others saw example item labels like “helpful, honest, forgiving.” Because both label types target the same underlying concept, switching labels between measurements provided an additional stress test of each method’s stability.

The experimental design was elegant in its simplicity. In Experiment 1a, 101 participants completed the ranking task twice; in Experiment 1b, 100 participants completed the BWS task twice; and in Experiment 2, 148 participants completed both tasks in randomized order. Participants were recruited through the online platform Prolific, restricted to native English speakers with high approval ratings, and paid at a rate commensurate with £9.00 per hour. The BWS task used a balanced pairwise design in which each of the ten life values appeared exactly six times across eleven subsets of five or six options, with any pair of values co-occurring exactly three times. Agreement between measurement occasions was quantified using Kendall’s Tau, a rank-correlation statistic bounded between −1 and 1, where a value of 1 indicates perfect agreement between two ordered lists.

The headline result was unambiguous. Average individual-level agreement between repeated measurements was substantially higher for BWS than for ranking, with mean Kendall’s Tau values of 0.69 versus 0.47—a difference supported by Bayes factors exceeding 1000, indicating decisive statistical evidence. The pattern of errors in the ranking task revealed exactly why. The most unstable position in the ranked list was rank six, smack in the middle: 81 percent of rank-six assignments changed between measurements. Consistency improved monotonically toward the extremes, with rank one changing for only 54 percent of responses. BWS, by capitalizing on people’s reliable judgments at the extremes, effectively avoids forcing respondents to manufacture precision in the muddled middle—precisely where rankings are weakest.

Importantly, the two methods were not measuring different things. The aggregate preference orderings agreed almost perfectly: benevolence emerged as the most important value and power as the least important in both tasks, and the top five values were ordered identically across methods, with only a single pair of middling values trading positions. The BWS scores, however, carried extra information that rankings cannot provide. Because normalized best–worst scores range continuously from −1 to 1, they quantify the strength of preferences, not just their order. In Experiment 2, the score gaps between first and second place and between ninth and tenth place were roughly 0.40 and 0.38, dwarfing the average gap of about 0.11 between adjacent middle ranks—confirming that middle-ranked options were nearly indistinguishable in preference strength. This added resolution has real-world value: in a prior oncology study cited by the authors, BWS revealed that surgeon training was twice as important to patients as surgeon experience and more than three times as important as hospital reputation.

The label manipulation produced a subtle but instructive finding. When the labels changed between measurement occasions—say, from “benevolence” to “helpful, honest, forgiving”—agreement dropped sharply for both methods, indicating that the two label sets evoke genuinely different interpretations of the same value. Yet the direction and even the relative magnitude of those interpretive shifts were consistent across both elicitation methods: benevolence was preferred as an item label and security as a dimension label, to similar degrees, whether measured by ranking or by BWS. This convergence suggests that the reliability advantage of BWS stems from the method itself rather than from any accidental alignment between the method and the particular stimulus set used.

The practical implications extend well beyond survey methodology. BWS is not free—completion times in the study ran about 8.6 minutes for the BWS task versus 4.6 minutes for ranking, because larger item sets require more choice rounds even though each round stays cognitively light. But the authors argue the added reliability is worth the cost, particularly in applied settings such as health care priority-setting, marketing research, and personality assessment, where item sets of 16 to 57 options make full rankings unwieldy. BWS also naturally captures ties, revealing when respondents genuinely hold two options equal, something a forced ranking can never show. For researchers who have long treated the humble ranked list as the default instrument for measuring what people want, the message of this study is clear: if you care whether your measurements would come out the same way twice, asking people only for their best and their worst may be the most honest question you can ask.

Subject of Research: Comparing the test–retest reliability of best–worst scaling and ranking methods for eliciting personal preferences

Article Title: Time after time, the best–worst scaling method is more reliable than ranking

Article References: Liang, G., Glover, M., & Hawkins, G. E. (2026). Time after time, the best–worst scaling method is more reliable than ranking. Behavior Research Methods, 58(10), Article 284. https://doi.org/10.3758/s13428-026-03167-x

Image Credits: AI Generated

DOI: 10.3758/s13428-026-03167-x

Keywords: best–worst scaling, ranking, preference elicitation, test–retest reliability, survey methods, life values, Schwartz Value Theory, Kendall's Tau, decision making, behavioral economics, psychological measurement, Behavior Research Methods