Imperial College London


Faculty of MedicineSchool of Public Health

Honoray Lecturer



+44 (0)20 7594 0923ranjeeta.thomas




LG 33AMedical SchoolSt Mary's Campus





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20 results found

Moorhouse L, Schaefer R, Thomas R, Nyamukapa C, Skovdal M, Hallett T, Gregson Set al., Application of the HIV prevention cascade to identify, develop,and evaluate interventions to improve use of prevention methods:Examples from a study in east Zimbabwe, Journal of the International AIDS Society, ISSN: 1758-2652

Introduction: The HIV prevention cascade could be used in developing interventions to strengthen implementation of efficacious HIV prevention methods but its practical utility needs to be demonstrated. We propose a standardised approach to using the cascade to guide identification and evaluation of interventions and demonstrate its feasibility through a project to develop interventions to improve use of HIV prevention methods by adolescent girls and young women (AGYW) and potential male partners in east Zimbabwe.Discussion: We propose a six-step approach to using a published generic HIV prevention cascade formulation to develop interventions to increase motivation to use, access to and effective use of an HIV prevention method. The six steps are: (1) measure the HIV prevention cascade for the chosen population and method; (2) identify gaps in the cascade; (3) identify explanatory factors (barriers) contributing to observed gaps; (4) review literature to identify relevant theoretical frameworks and interventions; (5) tailor interventions to the local context; and (6) implement and evaluate the interventions using the cascade steps and explanatory factors as outcome indicators in the evaluation design. In the Zimbabwe example, steps 1-5 aided development of four interventions to overcome barriers to effective use of PrEP in AGYW (15-24 years) and VMMC in male partners (15-29). For young men, prevention cascade analyses identified gaps in motivation and access (due to transport costs/lost income) as barriers to VMMC uptake, so an intervention was designed including financial incentives and an education session. For AGYW, gaps in motivation (particularly lack of risk perception) and access were identified as barriers to PrEP uptake: an interactive counselling game was developed addressing these barriers. A text messaging intervention was developed to improve adherence to PrEP among AGYW, addressing reasons underlying lack of effective PrEP use through improving the capa


Li Donni P, Thomas R, 2019, Latent class models for multiple ordered categorical health data: Testing violation of the local independence assumption, Empirical Economics, ISSN: 0377-7332

Latent class models are now widely applied in health economics to analyse heterogeneity in multiple outcomes generated by subgroups of individuals who vary in unobservable characteristics, such as genetic information or latent traits. These models rely on the underlying assumption that associations between observed outcomes are due to their relationship to underlying subgroups, captured in these models by conditioning on a set of latent classes. This implies that outcomes are locally independent within a class. Local independence assumption, however, is sometimes violated in practical applications when there is uncaptured unobserved heterogeneity resulting in residual associations between classes. While several approaches have been proposed in the case of binary and continuous outcomes, little attention has been directed to the case of multiple ordered categorical outcome variables often used in health economics. In this paper, we develop an approach to test for the violation of the local independence assumption in the case of multiple ordered categorical outcomes. The approach provides a detailed decomposition of identified residual association by allowing it to vary across latent classes and between levels of the ordered categorical outcomes within a class. We show how this level of decomposition is important in the case of ordered categorical outcomes. We illustrate our approach in the context of health insurance and healthcare utilization in the US Medigap market.


Thomas R, Friebel R, Barker K, Mwenge L, Kanema S, Vanqa N, Harper A, Bell-Mandla N, Smith P, Floyd S, Bock P, Ayles H, Fidler S, Hayes R, Hauck Ket al., 2019, Work and home productivity of people living with HIV in Zambia and South Africa, AIDS, ISSN: 0269-9370

Objective: To compare number of days lost to illness or accessing healthcare for HIV-positive and HIV-negative individuals working in the informal and formal sectors in South Africa and Zambia.Design: As part of the HPTN 071 (PopART) study, data on adults aged 18–44 years were gathered between in cross-sectional surveys of random general population samples in 21 communities in Zambia and South Africa. Data on the number of productive days lost in the last 3 months, laboratory-confirmed HIV status, labour force status, age, ethnicity, education, and recreational drug use was collected.Methods: Differences in productive days lost between HIV-negative and HIV-positive individuals (“excess productive days lost”) were estimated with negative binomial models, and results disaggregated for HIV-positive individuals after various durations on Anti-retroviral treatment (ART).Results: From samples of 19,330 respondents in Zambia and 18,004 respondents in South Africa, HIV-positive individuals lost more productive days to illness than HIV-negative individuals in both countries. HIV-positive individuals in Zambia lost 0.74 excess productive days (95%CI: 0.48–1.01; p < 0.001) to illness over a three-month period. HIV-positive in South Africa lost 0.13 excess days (95%CI: 0.04–0.23; p = 0.007). In Zambia, those on ART for less than one year lost most days, and those not on ART lost fewest days. In South Africa, results disaggregated by treatment duration were not statistically significant.Conclusions: There is a loss of work and home productivity associated with HIV, but it is lower than existing estimates for HIV-positive formal sector workers. The findings support policy makers in building an accurate investment case for HIV interventions.


Hauck K, Morton A, Chalkidou K, Chi Y-L, Culyer A, Levin C, Meacock R, Over M, Thomas R, Vassall A, Verguet S, Smith Pet al., 2019, How can we evaluate the cost-effectiveness of health system strengthening? A typology and illustrations, Social Science and Medicine, Vol: 220, Pages: 141-149, ISSN: 0277-9536

Health interventions often depend on a complex system of human and capital infrastructure that is shared with other interventions, in the form of service delivery platforms, such as healthcare facilities, hospitals, or community services. Most forms of health system strengthening seek to improve the efficiency or effectiveness of such delivery platforms. This paper presents a typology of ways in which health system strengthening can improve the economic efficiency of health services. Three types of health system strengthening are identified and modelled: (1) investment in the efficiency of an existing shared platform that generates positive benefits across a range of existing interventions; (2) relaxing a capacity constraint of an existing shared platform that inhibits the optimization of existing interventions; (3) providing an entirely new shared platform that supports a number of existing or new interventions. Theoretical models are illustrated with examples, and illustrate the importance of considering the portfolio of interventions using a platform, and not just piecemeal individual analysis of those interventions. They show how it is possible to extend principles of conventional cost-effectiveness analysis to identify an optimal balance between investing in health system strengthening and expenditure on specific interventions. The models developed in this paper provide a conceptual framework for evaluating the cost-effectiveness of investments in strengthening healthcare systems and, more broadly, shed light on the role that platforms play in promoting the cost-effectiveness of different interventions.


Schaefer R, Thomas R, Nyamukapa C, Maswera R, Kadzura N, Gregson Set al., 2018, Accuracy of HIV risk perception in east Zimbabwe 2003-2013, AIDS and Behavior, ISSN: 1090-7165

Risk perception for HIV infection is an important determinant for engaging in HIV prevention behaviour. We investigate the degree to which HIV risk perception is accurate, i.e. corresponds to actual HIV infection risks, in a general-population open-cohort study in Zimbabwe (2003–2013) including 7201 individuals over 31,326 person-years. Risk perception for future infection (no/yes) at the beginning of periods between two surveys was associated with increased risk of HIV infection (Cox regression hazard ratio = 1.38 [1.07–1.79], adjusting for socio-demographic characteristics, sexual behaviour, and partner behaviour). The association was stronger among older people (25+ years). This suggests that HIV risk perception can be accurate but the higher HIV incidence (1.27 per 100 person-years) illustrates that individuals may face barriers to HIV prevention behaviour even when they perceive their risks. Gaps in risk perception are underlined by the high incidence among those not perceiving a risk (0.96%), low risk perception even among those reporting potentially risky sexual behaviour, and, particularly, lack of accuracy of risk perception among young people. Innovative interventions are needed to improve accuracy of risk perception but barriers to HIV prevention behaviours need to be addressed too, which may relate to the partner, community, or structural factors.


Thomas R, Burger R, Hauck K, 2018, Richer, wiser and in better health? The socioeconomic gradient inhypertension prevalence, unawareness and control in South Africa, Social Science and Medicine, Vol: 217, Pages: 18-30, ISSN: 0277-9536

The socioeconomic gradient in chronic conditions is clear in the poorest and wealthiest of countries, but extant evidence on this relationship in low- and middle-income countries is inconclusive. We use data gathered between 2008-2012 from a nationally representative sample of over 10,000 South African adults, and objective health measures to analyse the differential effects of education, income and other factors on the prevalence of hypertension, individuals' awareness and control of hypertensive status. Prevalence of hypertension is high at 38% amongwomen and 34% among men. 59% of hypertensive individuals are unaware of their status. We and prevalence and unawareness of hypertension are a public health concern across all incomegroups in South Africa. Higher income is however associated with effective control amongst men. Completing secondary education is associated with 7 mmHg lower blood pressure only in a small sub-group of women but is associated with 22 percentage point higher likelihoodof effective hypertension control amongst women. We conclude that poorer and less educated individuals are particularly at high risk of cardiovascular disease in South Africa.


Morton A, Arulselvan A, Thomas RA, 2018, Allocation Rules for Global Donors., Journal of Health Economics, Vol: 58, Pages: 67-75, ISSN: 0167-6296

In recent years, donors such as the Bill and Melinda Gates Foundation have made an enormous contribution to the reduction of the global burden of disease. It has been argued that such donors should prioritise interventions based on their cost-effectiveness, that is to say, the ratio of costs to benefits. Against this, we argue that the donor should fund not the most cost-effective interventions, but rather interventions which are just cost-ineffective for the country, thus encouraging the country to contribute its own domestic resources to the fight against disease. We demonstrate that our proposed algorithm can be justified within the context of a model of the problem as a leader-follower game, in which a donor chooses to subsidise interventions which are implemented by a country. We argue that the decision rule we propose provides a basis for the allocation of aid money which is efficient, fair and sustainable.


Thomas RA, Burger R, Harper A, Kanema S, Mwenge L, Vanqa N, Bell-Mandla N, Smith P, Floyd S, Bock P, Ayles H, Beyers N, Donnell D, Fidler S, Hayes R, Hauck Ket al., 2017, Differences in health-related quality of life between HIV-positive and HIV-negative people in Zambia and South Africa: a cross-sectional baseline survey of the HPTN 071 (PopART) trial, The Lancet Global Health, Vol: 5, Pages: e1133-e1141, ISSN: 2214-109X

BackgroundThe life expectancy of HIV-positive individuals receiving antiretroviral therapy (ART) is approaching that of HIV-negative people. However, little is known about how these populations compare in terms of health-related quality of life (HRQoL). We aimed to compare HRQoL between HIV-positive and HIV-negative people in Zambia and South Africa.MethodsAs part of the HPTN 071 (PopART) study, data from adults aged 18–44 years were gathered between Nov 28, 2013, and March 31, 2015, in large cross-sectional surveys of random samples of the general population in 21 communities in Zambia and South Africa. HRQoL data were collected with a standardised generic measure of health across five domains. We used β-distributed multivariable models to analyse differences in HRQoL scores between HIV-negative and HIV-positive individuals who were unaware of their status; aware, but not in HIV care; in HIV care, but who had not initiated ART; on ART for less than 5 years; and on ART for 5 years or more. We included controls for sociodemographic variables, herpes simplex virus type-2 status, and recreational drug use.FindingsWe obtained data for 19 750 respondents in Zambia and 18 941 respondents in South Africa. Laboratory-confirmed HIV status was available for 19 330 respondents in Zambia and 18 004 respondents in South Africa; 4128 (21%) of these 19 330 respondents in Zambia and 4012 (22%) of 18 004 respondents in South Africa had laboratory-confirmed HIV. We obtained complete HRQoL information for 19 637 respondents in Zambia and 18 429 respondents in South Africa. HRQoL scores did not differ significantly between individuals who had initiated ART more than 5 years previously and HIV-negative individuals, neither in Zambia (change in mean score −0·002, 95% CI −0·01 to 0·001; p=0·219) nor in South Africa (0·000, −0·002 to 0·003; p=0·939). However, scores did differ between HIV-positive individu


Cundale K, Thomas R, Malaya JK, Havens D, Mortimer K, Conteh Let al., 2017, A health intervention or a kitchen appliance? Household costs and benefits of a cleaner burning biomass-fuelled cookstove in Malawi, SOCIAL SCIENCE & MEDICINE, Vol: 183, Pages: 1-10, ISSN: 0277-9536

Pneumonia is the leading cause of mortality for children under five years in sub-Saharan Africa. Household air pollution has been found to increase risk of pneumonia, especially due to exposure from dirty burning biomass fuels. It has been suggested that advanced stoves, which burn fuel more efficiently and reduce smoke emissions, may help to reduce household air pollution in poor, rural settings.This qualitative study aims to provide an insight into the household costs and perceived benefits from use of the stove in Malawi. It was conducted alongside The Cooking and Pneumonia Study (CAPS), the largest village cluster-level randomised controlled trial of an advanced combustion cookstove intervention to prevent pneumonia in children under five to date. In 2015, using 100 semi-structured interviews this study assessed household time use and perceptions of the stove from both control and intervention participants taking part in the CAPS trial in Chilumba. Household direct and indirect costs associated with the intervention were calculated.Users overwhelming liked using the stove. The main reported benefits were reduced cooking times and reduced fuel consumption. In most interviews, the health benefits were not initially identified as advantages of the stove, although when prompted, respondents stated that reduced smoke emissions contributed to a reduction in respiratory symptoms. The cost of the stove was much higher than most respondents said they would be willing to pay.The stoves were not primarily seen as health products. Perceptions of limited impact on health was subsequently supported by the CAPS trial data which showed no significant effect on pneumonia. While the findings are encouraging from the perspective of acceptability, without innovative financing mechanisms, general uptake and sustained use of the stove may not be possible in this setting. The findings also raise the question of whether the stoves should be marketed and championed as ‘health inte


Hauck KD, Thomas R, Smith P, 2017, Beyond Cost Effectiveness: Health Systems Constraints to Delivery of a Health Benefits Package, What's in What's out: Designing Benefits for Universal Health Coverage, Editors: Glassman, Giedion, Smith, Publisher: Center for Global Development, Pages: 201-213


Thomas RA, Chalkidou K, 2016, Cost–effectiveness analysis, Health System Efficiency How to Make Measurement Matter for Policy and Management, Editors: Smith, Cylus, Papanicolas, Publisher: European Observatory on Health Systems and Policies, ISBN: 9789289050418

In this book the authors explore the state of the art on efficiency measurement in health systems and international experts offer insights into the pitfalls and potential associated with various measurement techniques.


Heffernan A, Barber E, Thomas R, Fraser C, Pickles M, Cori Aet al., 2016, Impact and Cost-Effectiveness of Point-Of-Care CD4 Testing on the HIV Epidemic in South Africa., PLOS One, Vol: 11, ISSN: 1932-6203

Rapid diagnostic tools have been shown to improve linkage of patients to care. In the context of infectious diseases, assessing the impact and cost-effectiveness of such tools at the population level, accounting for both direct and indirect effects, is key to informing adoption of these tools. Point-of-care (POC) CD4 testing has been shown to be highly effective in increasing the proportion of HIV positive patients who initiate ART. We assess the impact and cost-effectiveness of introducing POC CD4 testing at the population level in South Africa in a range of care contexts, using a dynamic compartmental model of HIV transmission, calibrated to the South African HIV epidemic. We performed a meta-analysis to quantify the differences between POC and laboratory CD4 testing on the proportion linking to care following CD4 testing. Cumulative infections averted and incremental cost-effectiveness ratios (ICERs) were estimated over one and three years. We estimated that POC CD4 testing introduced in the current South African care context can prevent 1.7% (95% CI: 0.4% - 4.3%) of new HIV infections over 1 year. In that context, POC CD4 testing was cost-effective 99.8% of the time after 1 year with a median estimated ICER of US$4,468/DALY averted. In healthcare contexts with expanded HIV testing and improved retention in care, POC CD4 testing only became cost-effective after 3 years. The results were similar when, in addition, ART was offered irrespective of CD4 count, and CD4 testing was used for clinical assessment. Our findings suggest that even if ART is expanded to all HIV positive individuals and HIV testing efforts are increased in the near future, POC CD4 testing is a cost-effective tool, even within a short time horizon. Our study also illustrates the importance of evaluating the potential impact of such diagnostic technologies at the population level, so that indirect benefits and costs can be incorporated into estimations of cost-effectiveness.


Thomas RA, Morton A, Smith P, 2016, Decision rules for allocation of finances to health systems strengthening, Journal of Health Economics, Vol: 49, Pages: 97-108, ISSN: 0167-6296

A key dilemma in global health is how to allocate funds between disease-specific “vertical projects” on the one hand and “horizontal programmes” which aim to strengthen the entire health system on the other. While economic evaluation provides a way of approaching the prioritisation of vertical projects, it provides less guidance on how to prioritise between horizontal and vertical spending. We approach this problem by formulating a mathematical program which captures the complementary benefits of funding both vertical projects and horizontal programmes. We show that our solution to this math program has an appealing intuitive structure. We illustrate our model by computationally solving two specialised versions of this problem, with illustrations based on the problem of allocating funding for infectious diseases in sub-Saharan Africa. We conclude by reflecting on how such a model may be developed in the future and used to guide empirical data collection and theory development.


Gregson S, Fenton R, Nyamukapa C, Robertson L, Mushati P, Thomas R, Eaton Jet al., 2016, Wealth Differentials in the Impact of Conditional and Unconditional Cash Transfers on Education: Findings from a Community-Randomised Controlled Trial in Zimbabwe, Psychology, Health & Medicine, Vol: 21, Pages: 909-917, ISSN: 1354-8506

We investigated (1) how household wealth affected the relationshipbetween conditional cash transfers (CCT) and unconditional cashtransfers (UCT) and school attendance, (2) whether CCT and UCTaffected educational outcomes (repeating a year of school), (3) ifbaseline school attendance and transfer conditions affected howmuch of the transfers participants spent on education and (4) if CCTor UCT reduced child labour in recipient households. Data wereanalysed from a cluster-randomized controlled trial of CCT and UCTin 4043 households from 2009 to 2010. Recipient households received$18 dollars per month plus $4 per child. CCT were conditioned onabove 80% school attendance, a full vaccination record and a birthcertificate. In the poorest quintile, the odds ratio of above 80% schoolattendance at follow-up for those with below 80% school attendanceat baseline was 1.06 (p = .67) for UCT vs. CCT. UCT recipients reportedspending slightly more (46.1% (45.4–46.7)) of the transfer on schoolexpenses than did CCT recipients (44.8% (44.1–45.5)). Amongstthose with baseline school attendance of below 80%, there was nostatistically significant difference between CCT and UCT participantsin the proportion of the transfer spent on school expenses (p = .63).Amongst those with above 80% baseline school attendance, CCTparticipants spent 3.5% less (p = .001) on school expenses than UCTparticipants. UCT participants were no less likely than those in thecontrol group to repeat a grade of school. CCT participants had .69(.60–.79) lower odds vs. control of repeating the previous schoolgrade. Children in CCT recipient households spent an average of .31fewer hours in paid work than those in the control group (p < .001)and children in the UCT arm spent an average of .15 fewer hours inpaid work each week than those in the control arm (p = .06).


Hauck KD, Thomas R, Smith PC, 2016, Departures from cost-effectiveness recommendations: The impact of health system constraints on priority setting, Health Systems & Reform, Vol: 2, Pages: 61-70, ISSN: 2328-8604

The methods and application of cost-effectiveness analysis have reached an advanced stage of development. Many decision makers consider cost-effectiveness analysis to be a valid and feasible approach towards setting health priorities, and it has been extensively applied in evaluating interventions and developing evidence based clinical guidelines. However, the recommendations arising from cost-effectiveness analysis are often not implemented as intended. A fundamental reason for the failure to implement is that CEA assumes a single constraint, in the form of the budget constraint, whilst in reality decision-makers may be faced with numerous other constraints. The objective of this paper is to develop a typology of constraints that may act as barriers to implementation of cost-effectiveness recommendations. Six categories of constraints are considered: the design of the health system; costs of implementing change; system interactions between interventions; uncertainty in estimates of costs and benefits; weak governance; and political constraints. Where possible -and if applicable- for each class of constraint, the paper discusses ways in which these constraints can be taken into account by a decision maker wishing to pursue the principles of cost-effectiveness.


Anand P, Gray A, Liberini F, Roope L, Smith R, Thomas Ret al., 2015, Wellbeing over 50, JOURNAL OF THE ECONOMICS OF AGEING, Vol: 6, Pages: 68-78, ISSN: 2212-828X


Jones AM, Squire L, Thomas RA, 2010, Evaluating innovative health programs, Health Economics, Vol: 19(S1), Pages: 1-4, ISSN: 1057-9230

Identifying innovative interventi ons that meet critical health policy needs in local settings is likely to benefit from local knowledge. The Global Development Network’s (GDN) project ‘Evaluating Innovative Health Program s’ (EIHP) project is built on the ability of local researchers to identify such solutions. It evaluates the impact of 19 programs from across developing and transition countries that focus on the health-related Mill ennium Development Goals (MDGs) of reducing child and maternal mortality, and halting and reversing the trend of communicable diseases such as HIV/AIDS, malaria, and other diseases (United Nations, 2008). Local researchers are often be st placed to identify innovativesolutions to the problem faced in their countries. That said, identifying the impact of these interventions requires rigorous evaluations. The credibility of the findings depends on the quality of the evaluations.The research skills required to carry out these evaluations are not always available in these countries. Building long-term evaluation capacity is a key component of this project and has advantages both in terms of increasing the quality of the evaluations carried out under this project and also in encouraging future evaluations. To promote capacity building, a panel of international experts in impact evaluation was identified to act as mentors. Each research team was paired with a mentor through the duration of the evaluation. The panel of experts was drawn from leading academic institutions. The mentors provided active guidance in the design of the evaluation and the methods used. They facilitated transferof knowledge as well as ensuring evaluations met rigorous methodological standards. African and Asian policymakers from health and related ministries and practitioners from NGOs were involved in the project from its inception. A policymakers/practitioners panel, comprising African and Asian policymakers and practitioners, is a key element of the


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