Public contributors' preferences for the organization of remote public involvement meetings in health and social care: A discrete choice experiment study.

INTRODUCTION: Covid-19 expanded the use of remote working to engage with public contributors in health and social care research. These changes have the potential to limit the ability to participate in patient and public involvement and engagement (PPIE) for some public contributors. It is therefore important to understand public contributors' preferences, so that remote working can be organized in an optimal way to encourage rather than discourage participation. METHODS: We use an economic preference elicitation tool, a discrete choice experiment (DCE), via an online survey, to estimate public contributors' preferences for and trade-offs between different features of remote meetings. The features were informed by previous research to include aspects of remote meetings that were relevant to public contributors and amenable to change by PPIE organizers. RESULTS: We found that public contributors are more likely to participate in a PPIE project involving remote meetings if they are given feedback about participation; allowed to switch their camera off during meetings and step away if/when needed; were under 2.5 h long; organized during working hours, and are chaired by a moderator who can ensure that everyone contributes. Different combinations of these features can cause estimated project participation to range from 23% to 94%. When planning PPIE and engaging public contributors, we suggest that resources are focused on training moderators and ensuring public contributors receive meeting feedback. DISCUSSION AND CONCLUSION: Project resources should be allocated to maximize project participation. We provide recommendations for those who work in public involvement and organize meetings on how resources, such as time and financial support, should be allocated. These are based on the preferences of existing public contributors who have been involved in health and social care research. PATIENT OR PUBLIC CONTRIBUTION: We had a public contributor (Naheed Tahir) as a funded coapplicant on the UKRI ESRC application and involved members of the North West Coast Applied Research Collaboration (NWC ARC) Public Advisor Forum at every stage of the project. The survey design was informed from three focus groups held with NWC ARC public contributors. The survey was further edited and improved based on the results of six one-to-one meetings with public contributors.

Teleworking and housing demand.

The COVID-19 pandemic accelerated the trend towards teleworking. Many predicted that this would shift housing demand to the suburbs and homes with the potential for high quality office space. We examine these predictions using a survey of the working age population who live in the private housing sector. The majority in the sector are happy with their current home, but new teleworkers who plan to continue to do so - accounting for one fifth of the population - are characterised by a higher intention to move. Consistent with predictions, these teleworkers value a high quality home office more than others and are prepared to live further away from the centre to find it.

Is relational continuity of care as important to people as policy makers think? Preferences for continuity of care in primary care.

BACKGROUND: In 2005, the Portuguese government launched a Primary Care reform that aimed to reinforce continuity of care. After a promising start, the reform is still incomplete and continuity has been compromised by the lack of General Practice doctors. OBJECTIVE: This study evaluates public preferences for relational continuity of care alongside other attributes of Primary Care services in Portugal. METHODS: We use a discrete choice experiment (DCE) to evaluate preferences and estimate the population's willingness to pay (WTP) for Primary Care attributes. We use a sequential, mixed-methods approach to develop a D-efficient fractional factorial design for the DCE. Five attributes were included in the DCE and there were 32 DCE choice sets. The data collection was conducted in 2014 and the final sample had 517 respondents. A random parameters multinomial logit was used to analyse the data. RESULTS: We find that respondents value relational continuity of care, but that the current focus of the Portuguese NHS on relational continuity at the expense of other attributes is too simplistic. CONCLUSIONS: Relational continuity should be part of a broader policy that emphasizes person-centred care and considers the preferences of patients for Primary Care attributes.

Evaluating the Trade-Offs Men with Localized Prostate Cancer Make between the Risks and Benefits of Treatments: The COMPARE Study.

PURPOSE: The COMPARE (COMparing treatment options for ProstAte cancer) study aimed to evaluate and quantify the trade-offs patients make between different aspects of active surveillance and definitive therapy. MATERIALS AND METHODS: A discrete choice experiment tool was used to elicit patient preferences for different treatment characteristics in 34 urology departments. Patients with localized prostate cancer completed the discrete choice experiment within 1 week of being diagnosed and before they made treatment decisions. The discrete choice experiment was pretested (5) and piloted (106) with patients. Patients chose their preferred treatment profile based on the 6 characteristics of treatment type (active surveillance, focal therapy, radical therapy), return to normal activities, erectile function, urinary function, not needing more cancer treatment and 10 to 15-year cancer specific survival. Different tools were designed for patients with low-intermediate (468) and high risk (166) disease. An error components conditional logit model was used to estimate preferences and trade-offs between treatment characteristics. RESULTS: Patients with low-intermediate risk disease were willing to trade 6.99% absolute decrease in survival to have active surveillance over definitive therapy. They were willing to trade 0.75%, 0.46% and 0.19% absolute decrease in survival for a 1-month reduction in time to return to normal activities and 1% absolute improvements in urinary and sexual function, respectively. Patients with high risk disease were willing to trade 3.10%, 1.04% and 0.41% absolute decrease in survival for a 1-month reduction in time to return to normal activities and 1% absolute improvements in urinary and sexual function, respectively. CONCLUSIONS: Patients with low-intermediate risk prostate cancer preferred active surveillance to definitive therapy. Patients of all risk levels were willing to trade cancer specific survival for improved quality of life.

How Are Debriefing Questions Used in Health Discrete Choice Experiments? An Online Survey.

OBJECTIVES: Debriefing questions can assess if respondents understand discrete choice experiments (DCEs) and are answering in a way consistent with theories of decision making and utility maximization. Nevertheless, there is limited literature about how often debriefing questions are included or how the results are used in health economics. The aim of this study was to conduct a survey of the frequency, type, and analysis of debriefing questions in health DCEs. METHODS: We conducted an online survey of authors of published health DCEs, asking about their use of debriefing questions, including frequency, type, and analysis. We descriptively analyzed the sample characteristics and responses. Free-text questions were analyzed with qualitative thematic analysis. RESULTS: We received 70 responses (43% response rate), of which 50% reported using debriefing questions. They were most commonly designed to assess difficulty (91%), understanding (49%), and attribute nonattendance (31%) rather than learning effects (3%) or monotonicity (11%). On average, 37% of debriefing questions were analyzed (range, 0% to 69%), and the results were used <50% of the time, usually to exclude respondents or interpret overall results. Researcher experience or confidence with DCEs did not affect their use of debriefing questions. CONCLUSIONS: These results suggest that although half of researchers conducting health DCEs use debriefing questions, many do not analyze, use, or report the responses. Given the additional respondent burden, there is a need for reliable and valid debriefing questions. In the meantime, the inclusion, analysis, and reporting of debriefing questions should be carefully considered before DCE implementation.

Decision heuristic or preference? Attribute non-attendance in discrete choice problems.

This paper investigates if respondents' choice to not consider all characteristics of a multiattribute health service may represent preferences. Over the last decade, an increasing number of studies account for attribute non-attendance (ANA) when using discrete choice experiments to elicit individuals' preferences. Most studies assume such behaviour is a heuristic and therefore uninformative. This assumption may result in misleading welfare estimates if ANA reflects preferences. This is the first paper to assess if ANA is a heuristic or genuine preference without relying on respondents' self-stated motivation and the first study to explore this question within a health context. Based on findings from cognitive psychology, we expect that familiar respondents are less likely to use a decision heuristic to simplify choices than unfamiliar respondents. We employ a latent class model of discrete choice experiment data concerned with National Health Service managers' preferences for support services that assist with performance concerns. We present quantitative and qualitative evidence that in our study ANA mostly represents preferences. We also show that wrong assumptions about ANA result in inadequate welfare measures that can result in suboptimal policy advice. Future research should proceed with caution when assuming that ANA is a heuristic.

Patients' preferences and economic considerations play an important role in treatment decisions: a discrete choice experiment among rheumatologists.

OBJECTIVE: To evaluate to what extent rheumatologists consider economic aspects and patients' preferences when choosing drug treatments in patients with active RA. METHODS: In a discrete choice experiment, rheumatologists were asked to choose between two unlabelled drug treatment options for a hypothetical RA patient with moderate disease activity who failed two synthetic DMARDs. Attributes and levels of drug treatments were selected based on existing literature, rheumatologists' opinion and expert consensus. This resulted in five attributes each described by three levels: efficacy (level of improvement and achieved state on DAS28), safety (probability of a serious adverse event), patients' preference (level of agreement), annual medication costs and cost-effectiveness (incremental cost-effectiveness ratio). An efficient experimental design generated 14 treatment choices and a random parameter logit model estimated the relative importance of attributes. RESULTS: Sixty-three rheumatologists from the Netherlands contributed to the analysis; 44% were female and mean (sd) age was 49 (8) years. Drug efficacy had the strongest relative contribution to the drug choice (44%) followed by medication costs (24%), patients' preference (17%) and cost-effectiveness (14%). Patients' preferences were most relevant when patients disliked a proposed treatment. The risk of serious but uncommon or rare side effects only played a minor role in the treatment choice (1%). CONCLUSION: In addition to drug efficacy, rheumatologists account for economic aspects and for patients' preferences when deciding on drugs. Decisions are more influenced by absolute costs than relative cost-effectiveness and by patients' disliking as opposed to favouring the treatment.

Patients' preferences for anti-osteoporosis drug treatment: a cross-European discrete choice experiment.

Objectives: To estimate the preferences of osteoporotic patients for medication attributes, and analyse data from seven European countries. Methods: A discrete choice experiment was conducted in Belgium, France, Ireland, the Netherlands, Spain, Switzerland and the UK. Patients were asked to choose repeatedly between two hypothetical unlabelled drug treatments (and an opt-out option) that varied with respect to four attributes: efficacy in reducing the risk of fracture, type of potential common side effects, and mode and frequency of administration. In those countries in which patients contribute to the cost of their treatment directly, a fifth attribute was added: out-of-pocket cost. A mixed logit panel model was used to estimate patients' preferences. Results: In total, 1124 patients completed the experiment, with a sample of between 98 and 257 patients per country. In all countries, patients preferred treatment with higher effectiveness, and 6-monthly subcutaneous injection was always preferred over weekly oral tablets. In five countries, patients also preferred a monthly oral tablet and yearly i.v. injections over weekly oral tablets. In the three countries where the out-of-pocket cost was included as an attribute, lower costs significantly contributed to the treatment preference. Between countries, there were statistically significant differences for 13 out of 42 attribute/level interactions. Conclusion: We found statistically significant differences in patients' preferences for anti-osteoporosis medications between countries, especially for the mode of administration. Our findings emphasized that international treatment recommendations should allow for local adaptation, and that understanding individual preferences is important if we want to improve the quality of clinical care for patients with osteoporosis.

Re-Thinking 'The Different Perspectives That can be Used When Eliciting Preferences in Health'.

The 2003 Health Economics paper by Dolan, Olsen, Menzel and Richardson on 'An inquiry into the different perspectives that can be used when eliciting preferences in health' presents a conceptual framework of six perspectives along two dimensions: preferences (personal, social, and socially inclusive personal) and context (ex ante and ex post). The objective of our paper is to re-think this framework. We ask four questions concerning: the patient, or the user of the treatment; the payer of the treatment; the assessor of the value of treatment; and the timing of the illness and the nature of its risk. These questions refine the preference and context dimensions, and lead to the identification of perspectives not classified by the original framework. We propose an extended framework with five preferences (personal, non-use, proxy, social, and socially inclusive personal) and five contexts (one of which is ex post and four ex ante): since two of these cells are empty, this results in 23 possible perspectives. Online Supplementary Information presents 11 of these more formally to clearly distinguish between them and uses monetary and non-monetary (time trade-off) valuation tasks as examples. Copyright © 2017 John Wiley & Sons, Ltd.

Is Best-Worst Scaling Suitable for Health State Valuation? A Comparison with Discrete Choice Experiments.

Health utility indices (HUIs) are widely used in economic evaluation. The best-worst scaling (BWS) method is being used to value dimensions of HUIs. However, little is known about the properties of this method. This paper investigates the validity of the BWS method to develop HUI, comparing it to another ordinal valuation method, the discrete choice experiment (DCE). Using a parametric approach, we find a low level of concordance between the two methods, with evidence of preference reversals. BWS responses are subject to decision biases, with significant effects on individuals' preferences. Non parametric tests indicate that BWS data has lower stability, monotonicity and continuity compared to DCE data, suggesting that the BWS provides lower quality data. As a consequence, for both theoretical and technical reasons, practitioners should be cautious both about using the BWS method to measure health-related preferences, and using HUI based on BWS data. Given existing evidence, it seems that the DCE method is a better method, at least because its limitations (and measurement properties) have been extensively researched. Copyright © 2016 John Wiley & Sons, Ltd.

Discrete Choice Experiment Response Rates: A Meta-analysis.

This paper uses meta-regression analysis to test how aspects of discrete choice experiment (DCE) study design influence survey response rates. DCEs are a survey-based method used to elicit preferences for health and health care and are prone to survey errors of coverage, sampling, non-response and measurement. However, research on DCE response rates is lacking. Our analysis is motivated by a social exchange theory of survey response. We find that DCE response rates are related to the survey's cognitive burden and the relevance to the surveyed population. Copyright © 2016 John Wiley & Sons, Ltd.

What do UK medical students value most in their careers? A discrete choice experiment.

CONTEXT: Many individual- and job-related factors are known to influence medical careers decision making. Previous research has extensively studied medical trainees' (residents') and students' views of the factors that are important. However, how trainees and students trade off these factors at times of important careers-related decision making is under-researched. Information about trade-offs is crucial to the development of effective policies to enhance the recruitment and retention of junior doctors. OBJECTIVES: Our aim was to investigate the strength of UK medical students' preferences for the characteristics of training posts in terms of monetary value. METHODS: We distributed a paper questionnaire that included a discrete choice experiment (DCE) to final-year medical students in six diverse medical schools across the UK. The main outcome measure was the monetary value of training post characteristics, based on willingness to forgo and willingness to accept extra income for a change in each job characteristic calculated from regression coefficients. RESULTS: A total of 810 medical students answered the questionnaire. The presence of good working conditions was by far the most influential characteristic of a training position. Medical students consider that, as newly graduated doctors, they will require compensation of an additional 43.68% above average earnings to move from a post with excellent working conditions to one with poor working conditions. Female students value excellent working conditions more highly than male students, whereas older medical students value them less highly than younger students. CONCLUSIONS: Students on the point of completing medical school and starting postgraduate training value good working conditions significantly more than they value desirable geographical location, unit reputation, familiarity with the unit or opportunities for partners or spouses. This intelligence can be used to address the crisis in workforce staffing that has developed in the UK and opens up fruitful areas for future research across contexts and in terms of examining stated preferences versus actual career-related behaviour.

What do UK doctors in training value in a post? A discrete choice experiment.

CONTEXT: Many individual and job-related factors are known to influence medical careers decision making. Medical trainees' (residents) views of which characteristics of a training post are important to them have been extensively studied but how they trade-off these characteristics is under-researched. Such information is crucial for the development of effective policies to enhance recruitment and retention. Our aim was to investigate the strength of UK foundation doctors' and trainees' preferences for training post characteristics in terms of monetary value. METHODS: We used an online questionnaire study incorporating a discrete choice experiment (DCE), distributed to foundation programme doctors and doctors in training across all specialty groups within three UK regions, in August-October 2013. The main outcome measures were monetary values for training-post characteristics, based on willingness to forgo and willingness to accept extra income for a change in each job characteristic, calculated from regression coefficients. RESULTS: The questionnaire was answered by 1323 trainees. Good working conditions were the most influential characteristics of a training position. Trainee doctors would need to be compensated by an additional 49.8% above the average earnings within their specialty to move from a post with good working conditions to one with poor working conditions. A training post with limited rather than good opportunities for one's spouse or partner would require compensation of 38.4% above the average earnings within their specialty. Trainees would require compensation of 30.8% above the average earnings within their specialty to move from a desirable to a less desirable locality. These preferences varied only to a limited extent according to individual characteristics. DISCUSSION: Trainees place most value on good working conditions, good opportunities for their partners and desirable geographical location when making career-related decisions. This intelligence can be used to develop alternative models of workforce planning or to develop information about job opportunities that address trainees' values.

Stability of Willingness to Pay: Does Time and Treatment Allocation in a Randomized Controlled Trial Influence Willingness to Pay?

BACKGROUND: Willingness-to-pay (WTP) estimates are useful to policy makers only if they are generalizable beyond the moment when they are collected. To understand the "shelf life" of preference estimates, preference stability needs be tested over substantial periods of time. METHODS: We tested the stability of WTP for preventative dental care (scale and polish) using a payment-card contingent valuation question administered to 909 randomized controlled trial participants at 4 time points: baseline (prerandomization) and at annual intervals for 3 years. Trial participants were regular attenders at National Health Service dental practices. Participants were randomly offered different frequencies (intensities) of scale polish (no scale and polish, 1 scale and polish per year, 2 scale and polishes per year). We also examined whether treatment allocation to these different treatment intensities influenced the stability of WTP. Interval regression methods were used to test for changes in WTP over time while controlling for changes in 2 determinants of WTP. Individual-level changes were also examined as well as the WTP function over time. RESULTS: We found that at the aggregate level, mean WTP values were stable over time. The results were similar by trial arm. Individuals allocated to the arm with the highest scale and polish intensity (2 per year) had a slight increase in WTP toward the latter part of the trial. There was considerable variation at the individual level. The WTP function was stable over time. CONCLUSIONS: The payment-card contingent valuation method can produce stable WTP values in health over time. Future research should explore the generalizability of these results in other populations, for less familiar health care services, and using alternative elicitation methods. HIGHLIGHTS: Stated preferences are commonly used to value health care.Willingness-to-pay (WTP) estimates are useful only if they have a "shelf life."Little is known about the stability of WTP for health care.We test the stability of WTP for dental care over 3 y.Our results show that the contingent valuation method can produce stable WTP values.

Preferences of Recent Mums in Remote and Rural Areas for Type of Intrapartum Care: A Discrete Choice Experiment.

BACKGROUND AND OBJECTIVES: Pregnant women living in rural areas considering their preferred place of birth may have to 'trade-off' travel time/distance and other attributes of care (e.g. the full choice of birthplace options is rarely available locally). This study assesses the preferences and trade-offs of recent mothers who live in remote and rural areas of Great Britain. METHODS: An online survey, informed by qualitative research, was administered to women living in rural areas who had given birth in the preceding 3 years. The survey included a discrete choice experiment (DCE) to elicit women's preferences and trade-offs for place of birth. The DCE presented women with a series of eight choice tasks in which place of birth was defined by four attributes: (1) type of facility, (2) familiarity with staff, (3) understanding options and feel relaxed and reassured and (4) the travel time to the place of intrapartum care. DCE data were analysed using an error components logit model to identify preferences. RESULTS: Across 251 survey responses, holding everything else equal, respondents preferred: intrapartum care in locations with more specialist staff and equipment, locations where they understood their options and felt reassured and where travel time was minimal. Women were willing to travel (92-183 min) to a well-staffed and equipped facility if they understood their options and felt relaxed and reassured. Willingness to travel was reduced if the care received at the specialist facility was such that they did not understand their options and felt tense and powerless (41-132 min). CONCLUSION: These insights into the preferences of recent mums from remote and rural areas could inform future planning of rural intrapartum care.

Public preferences and willingness to pay for a net zero NHS: a protocol for a discrete choice experiment in England and Scotland.

INTRODUCTION: Climate change poses a major threat to our health, livelihoods and the planet. In 2020, the UK National Health Service (NHS) committed to reducing its Scope 1, 2 and 3 emissions to reach net zero by 2045. Although a net zero NHS would help to limit the consequences of climate change, little is known about the UK general public's values and preferences for the proposed service changes needed to reach net zero. METHODS: This study will elicit the public's preferences for actions to help achieve net zero NHS in England and Scotland using a discrete choice experiment (DCE). The DCE attributes and levels describe actions that can be taken by the NHS across key areas: buildings and estates, outdoor space, travel and transport, provision of care, goods and services and food and catering. The survey was designed using online think-aloud interviews with 17 members of the public. Two versions of the survey will be administered to a sample of up to 2200 respondents. One will include a payment vehicle as income tax increases. We will estimate the relative importance of each attribute and, for the former survey, the monetary trade-offs which individuals are willing to make between attributes. Where possible, we will match both samples to gauge preference robustness with the inclusion of the monetary payment. We will test whether respondents' preferences differ based on their socioeconomic circumstances and attitudes toward the NHS and climate change. ETHICS AND DISSEMINATION: The University of Aberdeen's School of Medicine, Medical Sciences and Nutrition Ethics Research Board has approved the study (reference: SERB/690090). All participants will provide informed consent. Results will be submitted to peer-reviewed publications and presented at relevant conferences and seminars. A lay summary of the research will be published on the Health Economics Research Unit website.

Patients' Preferences for Cytoreductive Treatments in Newly Diagnosed Metastatic Prostate Cancer: The IP5-MATTER Study.

BACKGROUND AND OBJECTIVE: Cytoreductive treatments for patients diagnosed with de novo synchronous metastatic hormone-sensitive prostate cancer (mHSPC) confer incremental survival benefits over systemic therapy, but these may lead to added toxicity and morbidity. Our objective was to determine patients' preferences for, and trade-offs between, additional cytoreductive prostate and metastasis-directed interventions. METHODS: A prospective multicentre discrete choice experiment trial was conducted at 30 hospitals in the UK between December 3, 2020 and January 25, 2023 (NCT04590976). The individuals were eligible for inclusion if they were diagnosed with de novo synchronous mHSPC within 4 mo of commencing androgen deprivation therapy and had performance status 0-2. A discrete choice experiment instrument was developed to elicit patients' preferences for cytoreductive prostate radiotherapy, prostatectomy, prostate ablation, and stereotactic ablative body radiotherapy to metastasis. Patients chose their preferred treatment based on seven attributes. An error-component conditional logit model was used to estimate the preferences for and trade-offs between treatment attributes. KEY FINDINGS AND LIMITATIONS: A total of 352 patients were enrolled, of whom 303 completed the study. The median age was 70 yr (interquartile range [IQR] 64-76) and prostate-specific antigen was 94 ng/ml (IQR 28-370). Metastatic stages were M1a 10.9% (33/303), M1b 79.9% (242/303), and M1c 7.6% (23/303). Patients preferred treatments with longer survival and progression-free periods. Patients were less likely to favour cytoreductive prostatectomy with systemic therapy (Coef. -0.448; [95% confidence interval {CI} -0.60 to -0.29]; p < 0.001), unless combined with metastasis-directed therapy. Cytoreductive prostate radiotherapy or ablation with systemic therapy, number of hospital visits, use of a "day-case" procedure, or addition of stereotactic ablative body radiotherapy did not impact treatment choice. Patients were willing to accept an additional cytoreductive treatment with 10 percentage point increases in the risk of urinary incontinence and fatigue to gain 3.4 mo (95% CI 2.8-4.3) and 2.7 mo (95% CI 2.3-3.1) of overall survival, respectively. CONCLUSIONS AND CLINICAL IMPLICATIONS: Patients are accepting of additional cytoreductive treatments for survival benefit in mHSPC, prioritising preservation of urinary function and avoidance of fatigue. PATIENT SUMMARY: We performed a large study to ascertain how patients diagnosed with advanced (metastatic) prostate cancer at their first diagnosis made decisions regarding additional available treatments for their prostate and cancer deposits (metastases). Treatments would not provide cure but may reduce cancer burden (cytoreduction), prolong life, and extend time without cancer progression. We reported that most patients were willing to accept additional treatments for survival benefits, in particular treatments that preserved urinary function and reduced fatigue.

The Perception of Women in Rural and Remote Scotland About Intrapartum Care: A Qualitative Study.

BACKGROUND: The views of mothers are important in shaping policy and practice regarding options for intrapartum care. Mothers in rural and remote areas face unique challenges accessing services, and these need to be well understood. Therefore, our aim was to understand the compromises that women who live in remote and rural settings, more than 1 h from a maternity unit, face regarding intrapartum care. METHODS: Qualitative semi-structured telephone interviews (n = 14) were undertaken in rural Scotland with 13 women who had young children and one who was pregnant. Interviews were transcribed and thematically analysed by two researchers. RESULTS: Key themes identified were women's perceptions about risk and the safety of different pathways of maternity care and birth locations; the actual and perceived distance between home and the place of birth, and the type of maternity care available at a place of birth. Mothers in rural and remote areas face particular challenges in choosing where to have their babies. In addition to clinical decisions about 'place of birth' agreed with healthcare professionals, they have to mentally juggle the implications of giving birth when at a distance from family support and away from familiar surroundings. It was clear that many women from rural communities have a strong sense of 'place' and that giving birth in a geographical location, community and culture that feels familiar is important to many of them. CONCLUSIONS: Health care staff need to appreciate the impact of non-clinical factors that are important to mothers in remote and rural areas and acknowledge these, even when they cannot be accommodated. Local and national policy also needs to reflect and respond to the practical challenges faced by rurality.

Trace gas detection of molecular hydrogen H(2) by photoacoustic stimulated Raman spectroscopy (PARS).

Photoacoustic stimulated Raman spectroscopy (PARS) has been used for sensitive and selective trace gas detection of molecular hydrogen under ambient conditions. In one experiment, 532 nm output of a seeded pulsed Nd:YAG laser is employed as Raman pump source and a Raman shifter filled with gaseous H(2) to obtain Stokes shifted radiation at 683 nm, suitable to stimulate H(2) Raman detection in a photoacoustic cell. A noise equivalent detection limit of 40 ppm by volume H(2) in 1 atm N(2) is obtained (14 mJ at 532 nm, 18 mJ at 683 nm, 10 Hz repetition rate, 58 s measurement time). Another experiment employs a dye laser for stimulating Raman radiation between 681-684 nm, allowing tuneable PARS. A Gaussian spectral fitting procedure has been applied giving a noise equivalent detection limit of 4.6 ppm by volume H(2) in 1 atm N(2) (35 mJ pulse energy at 532 nm, 45 mJ at 681-684 nm, 10 Hz repetition rate, 256 s measurement time). Spectroscopic detection offers the advantage of high selectivity along with the ability to obtain temperature and dynamic information from the rotational population and a line shape analysis, and also allows the discrimination between ortho- and para-H(2).