1. Cyhoeddwyd

   Public funding of drugs for orphan diseases

   Hughes, D. & Hughes, D. A., 1 Tach 2005.

   Allbwn ymchwil: Cyfraniad at gynhadledd › Papur

2. Cyhoeddwyd

   Public funding of drugs for orphan diseases

   Hughes, D. & Hughes, D. A., 1 Ion 2006.

   Allbwn ymchwil: Cyfraniad at gynhadledd › Papur

3. Cyhoeddwyd

   Public funding of drugs for orphan diseases

   Hughes, D. & Hughes, D. A., 1 Gorff 2005.

   Allbwn ymchwil: Cyfraniad at gynhadledd › Papur

4. Cyhoeddwyd

   Public health interventions to promote mental well-being in people aged 65 and over: systematic review of effectiveness and cost-effectiveness.

   Hughes, D., Windle, G., Hughes, D. A., Linck, P., Morgan, R., Burholt, V., Edwards, R. T., Reeves, C., Yeo, S. T., Woods, R. T. & Russell, I. T., 1 Ion 2007, 2007 gol. Unknown.

   Allbwn ymchwil: Llyfr/Adroddiad › Adroddiad Comisiwn

5. Cyhoeddwyd

   Public health interventions to promote well-being in people aged 65 and over: systematic review of effectiveness and cost-effectiveness.

   Hughes, D., Linck, P. G., Windle, G., Hughes, D. A., Linck, P., Russell, I. T., Morgan, R., Woods, R. T., Burholt, V., Edwards, R. T., Reeves, C. & Yeo, S. T., 1 Ion 2008, 2008 gol. Unknown.

   Allbwn ymchwil: Llyfr/Adroddiad › Adroddiad Comisiwn

6. Cyhoeddwyd

   Public health interventions to promote well-being in people aged 65 and over: systematic review of effectiveness and cost-effectiveness: Evidence Tables.

   Hughes, D., Linck, P. G., Windle, G., Linck, P., Morgan, R., Hughes, D. A., Burholt, V., Reeves, C., Yeo, S. T., Woods, R. T., Edwards, R. T. & Russell, I. T., 1 Ion 2008, 2008 gol. Unknown.

   Allbwn ymchwil: Llyfr/Adroddiad › Adroddiad Comisiwn

7. Cyhoeddwyd

   Public meetings of the NICE appraisals committee

   Hughes, D. & Hughes, D. A., 1 Rhag 2007.

   Allbwn ymchwil: Cyfraniad at gynhadledd › Papur

8. Cyhoeddwyd

   Pump-Downloaded Insulin Usage For The First 12 Months In A Cohort of Children Newly-Diagnosed With Type 1 Diabetes (T1D)

   Ridyard, C., Blair, J. & Hughes, D., Tach 2017, Yn: Value in Health. 20, 9, t. A481 - A482

   Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

9. Cyhoeddwyd

   Quantitative evidence synthesis methods for the assessment of the effectiveness of treatment sequences for clinical and economic decision-making: a review and taxonomy of simplifying assumptions

   Lewis, R., Hughes, D., Sutton, AJ. & Wilkinson, C., Ion 2021, Yn: PharmacoEconomics. 39, 1, t. 25-61 37 t.

   Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

10. Cyhoeddwyd

    Quantitative risk-benefit analysis

    Hughes, D. & Hughes, D. A., 1 Mai 2007.

    Allbwn ymchwil: Cyfraniad at gynhadledd › Papur

11. Cyhoeddwyd

    RES00019. Wales COVID-19 Evidence Centre. A rapid evidence summary indicating the evidence of the inverse care law in social care in Wales and has this been exacerbated by the COVID-19 pandemic?

    Spencer, L., Hendry, A., Makanjuola, A., Hughes, D., Wilkinson, C., Pisavadia, K., Davies, J., Fitzsimmons, D. & Edwards, R. T., Chwef 2022, Welsh Government. 33 t.

    Allbwn ymchwil: Llyfr/Adroddiad › Adoddiad Arall

12. Cyhoeddwyd

    RES00038. Wales COVID-19 Evidence Centre. A rapid evidence summary of the cost impact of Long COVID on employment and caring responsibilities

    Spencer, L., Hendry, A., Davies, J., Pisavadia, K., Hughes, D. & Edwards, R. T., Mai 2022, Welsh Government. 18 t.

    Allbwn ymchwil: Llyfr/Adroddiad › Adoddiad Arall

13. Cyhoeddwyd

    Rare Disease Terminology and Definitions—A Systematic Global Review: Report of the ISPOR Rare Disease Special Interest Group

    Hughes, D., Richter, T., Nestler-Parr, S., Babela, R., Khan, Z. M., Tesoro, T., Molsen, E. & Hughes, D. A., 18 Awst 2015, Yn: Value in Health. 18, 6, t. 906-914

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

14. Cyhoeddwyd

    Rare disease prevention and treatment: The need for a level playing field

    Hughes, D. & Plumpton, C., Chwef 2018, Yn: Pharmacogenomics. 19, 3, t. 243-247

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

15. Cyhoeddwyd

    Rationing of drugs for rare diseases

    Hughes, D. & Hughes, D. A., 1 Ebr 2006.

    Allbwn ymchwil: Cyfraniad at gynhadledd › Papur

16. Cyhoeddwyd

    Rationing of drugs for rare diseases.

    Hughes, D. & Hughes, D. A., 1 Ion 2006, Yn: Pharmacoeconomics. 24, 4, t. 315-316

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

17. Cyhoeddwyd

    Reimbursement Decisions of the All Wales Medicines Strategy Group

    Hughes, D., Linley, W. G. & Hughes, D. A., 1 Medi 2012, Yn: PharmoEconomics. 30, 9, t. 779-794

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

18. Cyhoeddwyd

    Renal transplant patients’ preference for the supply and delivery of immunosuppressants in Wales: A discrete choice experiment

    Hagemi, A., Plumpton, C. & Hughes, D., 2 Hyd 2017, Yn: BMC Nephrology. 18, 305.

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

19. Cyhoeddwyd

    Resource-Use Measurement Based on Patient Recall: Issues and Challenges for Economic Evaluation

    Thorn, J. C., Coast, J., Cohen, D., Hollingworth, W., Knapp, M., Noble, S. M., Ridyard, C. H., Wordsworth, S. & Hughes, D., 1 Meh 2013, Yn: Applied Health Economics and Health Policy. 11, 3, t. 155-161

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

20. Cyhoeddwyd

    Review of resource-use measures in UK economic evaluations

    Ridyard, C. & Hughes, D., 2015, PSSRU Unit Costs of Health and Social Care 2015 . Curtis, L. & Burns, A. (gol.). University of Kent, Canterbury, t. 22-31 10 t.

    Allbwn ymchwil: Pennod mewn Llyfr/Adroddiad/Trafodion Cynhadledd › Pennod › adolygiad gan gymheiriaid

21. Cyhoeddwyd

    Review of the Use of Resource Use Instruments Based on Patient Recall in Relation to Other Methods of Cost Estimation

    Ridyard, C. & Hughes, D., Tach 2013.

    Allbwn ymchwil: Cyfraniad at gynhadledd › Papur › adolygiad gan gymheiriaid

22. Cyhoeddwyd

    Review of the use of resource use instruments based on patient recall in relation to other methods of resource use estimation

    Ridyard, C. & Hughes, D., Tach 2013.

    Allbwn ymchwil: Cyfraniad at gynhadledd › Papur › adolygiad gan gymheiriaid

23. Cyhoeddwyd

    Screening log data can be used to inform protocol modifications, increasing patient recrutiment to a challanging clinical trial

    Blair, J., Awoyale, L., Thornborough, K., Peak, M., Didi, M., Bedson, E., Hughes, D., Ridyard, C., Tat, T. & Gregory, J., Tach 2013.

    Allbwn ymchwil: Cyfraniad at gynhadledd › Papur › adolygiad gan gymheiriaid

24. Cyhoeddwyd

    Seizure First Aid Training For people with Epilepsy (SAFE) frequently attending emergency departments and their significant others: results of a UK multi-centre randomised controlled pilot trial

    Noble, A. J., Snape, D., Nevitt, S., Holmes, E., Morgan, M., Smith, C. T., Hughes, D., Buchanan, M., McVicar, J., MacCallum, E., Goodacre, S., Rinsdale, L. & Marson, A. G., 16 Ebr 2020, Yn: BMJ Open. 10, 4, e035516.

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

25. Cyhoeddwyd

    Service users' preferences and feasibility – which alternative care pathway for adult ambulance users achieves the optimal balance? Workshops for the COLLABORATE project

    Noble, A. J., Morris, B., Dixon, P., Mathieson, A., Ridsdale, L., Morgan, M., Dickson, J., Goodacre, S., Jackson, M., Hughes, D., Marson, A. & Holmes, E., Ebr 2024, Yn: Seizure: European Journal of Epilepsy. 118, t. 17-27

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

26. Cyhoeddwyd

    Silver-impregnated, antibiotic-impregnated or non-impregnated ventriculoperitoneal shunts to prevent shunt infection: the BASICS three-arm RCT

    Mallucci, C. L., Jenkinson, M., Conroy, E. J., Hartley, J. C., Brown, M., Moitt, T., Dalton, J., Kearns, T., Griffiths, M. J., Culeddu, G., Solomon, T., Hughes, D. & Gamble, C., 2 Ebr 2020, Yn: Health Technology Assessment. 24, 17, 114 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

27. Cyhoeddwyd

    Societal perspective on access to publicly subsidised medicines: A cross sectional survey of 3080 adults in Australia

    Chim, L., Salkeld, G., Kelly, P., Lipworth, W., Hughes, D. & Stockler, M., 1 Maw 2017, Yn: PLoS ONE.

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

28. Cyhoeddwyd

    Societal preferences for funding orphan drugs in the United Kingdom: An application of person trade off and discrete choice experiment methods

    Bourke, S. M., Plumpton, C. & Hughes, D., 9 Mai 2018, Yn: Value in Health. 21, 5, t. 538-546

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

29. Cyhoeddwyd

    Societal views on NICE, cancer drugs fund and value-based pricing criteria for prioritising medicines: a cross-sectional survey of 4118 adults in Great Britain

    Hughes, D., Linley, W. G. & Hughes, D. A., 1 Awst 2013, Yn: Health Economics. 22, 8, t. 948-964

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

30. Cyhoeddwyd

    Statistical Methods for Adjusting Estimates of Treatment Effectiveness for Patient Non-adherence in the Context of Time-to-Event Outcomes and Health Technology Assessment: A Systematic Review of Methodological Papers

    Alshreef, A., Latimer, N., Tappenden, P., Wong, R., Hughes, D., Fotheringham, J. & Dixon, S., Tach 2019, Yn: Medical Decision Making. 39, 8, t. 910-925 16 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

31. Cyhoeddwyd

    Statistical comments are unfounded.

    Hughes, D., Hughes, D. A., Cowell, W., Koncz, T. & Cramer, J., 1 Maw 2008, Yn: Value in Health. 11, 2, t. 346

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

32. Cyhoeddwyd

    Study protocol for a pragmatic randomised controlled trial comparing the effectiveness and cost effectiveness of levetiracetam and zonisamide versus standard treatments for epilepsy: a comparison of Standard And New Antiepileptic Drugs (SANAD-II)

    Balabanova, S., Taylor, C., Sills, G., Burnside, G., Plumpton, C., Smith, P., Appleton, R., Leach, J. P., Johnson, M., Baker, G. A., Pirmohamed, M., Hughes, D., Williamson, P., Tudor-Smith, C. & Marson, A. G., 26 Awst 2020, Yn: BMJ Open. 10, 8, e040635.

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

33. Cyhoeddwyd

    Study protocol for a randomised controlled trial of insulin delivery by continuous subcutaneous infusion compared to multiple daily injections

    Blair, J., Gregory, J., Hughes, D., Ridyard, C., Gamble, C., McKay, A., Didi, M., Thornborough, K., Bedson, E., Awoyale, L., Cwiklinski, E. & Peak, M., 16 Ebr 2015, Yn: Trials. 16, 163.

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

34. Cyhoeddwyd

    Subcutaneous Injection of Adalimumab Trial compared with Control (SCIATiC): a randomised controlled trial of adalimumab injection compared with placebo for patients receiving physiotherapy treatment for sciatica

    Williams, N. H., Jenkins, A., Goulden, N., Hoare, Z., Hughes, D. A., Wood, E., Foster, N. E., Walsh, D. A., Carnes, D., Sparkes, V., Hay, E. M., Isaacs, J., Konstantinou, K., Morrissey, D., Karppinen, J., Genevay, S. & Wilkinson, C., 31 Hyd 2017, Yn: Health Technology Assessment. 21, 60, t. 1-180 180 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

35. Cyhoeddwyd

    Superiority and cost-effectiveness of monthly extended-release buprenorphine versus daily standard of care medication: a pragmatic, parallel-group, open-label, multicentre, randomised, controlled, phase 3 trial

    Marsden, J., Kelleher, M., Gilvarry, E., Mitcheson, L., Bisla, J., Cape, A., Cowden, F., Day, E., Dewhurst, J., Evans, R., Hardy, W., Hearn, A., Kelly, J., Lowry, N., McCusker, M., Murphy, C., Murray, R., Myton, T., Quarshie, S., Vanderwaal, R., Wareham, A., Hughes, D. & Hoare, Z., Rhag 2023, Yn: eClinicalMedicine. 66, 23 t., 102331.

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

36. Cyhoeddwyd

    Supply-side cost-effectiveness thresholds: questions for evidence-based policy

    Sampson, C., Zamora, B., Watson, S., Cairns, J., Chalkidou, K., Cubi-Molla, P., Devlin, N., García-Lorenzo, B., Hughes, D., Leech, A. & Towse, A., Medi 2022, Yn: Applied Health Economics and Health Policy. 20, 5, t. 651-667

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

37. Cyhoeddwyd

    Supporting People With Type 2 Diabetes in the Effective Use of Their Medicine Through Mobile Health Technology Integrated With Clinical Care to Reduce Cardiovascular Risk: Protocol for an Effectiveness and Cost-effectiveness Randomized Controlled Trial

    Farmer, A. J., Jones, L., Newhouse, N., Kenning, C., Williams, N., Chi, Y., Bartlett, K., Plumpton, C., McSharry, J., Cholerton, R., Holmes, E., Robinson, S., Allen, J., Gudgin, B., Velardo, C., Rutter, H., Horne, R., Tarassenko, L., Williams, V., Locock, L., Rea, R., Yu, L-M., Hughes, D., Bower, P. & French, D. P., 21 Chwef 2022, Yn: JMIR Research Protocols. 11, 2, e32918.

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

38. Cyhoeddwyd

    Supporting people with type 2 diabetes in effective use of their medicine through mobile health technology integrated with clinical care (SuMMiT-D Feasibility): a randomised feasibility trial protocol

    Farmer, A. J., Allen, J., Bartlett, K., Bower, P., Chi, Y., French, D. P., Gudgin, B., Holmes, E., Horne, R., Hughes, D., Kenning, C., Locock, L., McSharry, J., Miles, L., Newhouse, N., Rea, R., Riga, J., Tarassenko, L., Velardo, C., Williams, N., Williams, V. & Yu, L-M., 29 Rhag 2019, Yn: BMJ Open. 9, 12, e033504.

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

39. E-gyhoeddi cyn argraffu

    Supporting people with type 2 diabetes in effective use of their medicine through mobile health technology integrated with clinical care (SuMMiT-D pilot): results of a feasibility randomised trial

    SuMMiT-D Collaborative Group , 25 Ion 2024, (E-gyhoeddi cyn argraffu) Yn: Pilot and Feasibility Studies. 10, 1, 15.

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

40. Cyhoeddwyd

    Surgical microdiscectomy versus transforaminal epidural steroid injection in patients with sciatica secondary to herniated lumbar disc (NERVES): a phase 3, multicentre, open-label, randomised controlled trial and economic evaluation

    Wilby, M. J., Best, A., Wood, E., Burnside, G., Bedson, E., Short, H., Wheatley, D., Hill-McManus, D., Sharma, M., Clark, S., Baranidharan, G., Price, C., Mannion, R., Hutchinson, P. J., Hughes, D., Marson, A. G. & Williamson, P., 1 Mai 2021, Yn: The Lancet Rheumatology. 3, 5, t. e347-e356

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

41. Cyhoeddwyd

    Systematic Review: Outcomes and adverse events from randomised trials in Crohn's disease

    Catt, H., Hughes, D., Kirkham, J. K. & Bodger, K., Ebr 2019, Yn: Alimentary Pharmacology and Therapeutics. 49, 8, t. 978-996 19 t.

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

42. Cyhoeddwyd

    Systematic review of follow-up of cancer in primary care verses secondary care: findings for breast and lung cancer

    Hughes, D., Lewis, R., Neal, R. D., France, B., Williams, N. H., Wilkinson, C., Russell, I. T., Russell, D., Hughes, D. A., Stuart, N. S. & Weller, D., 1 Maw 2007.

    Allbwn ymchwil: Cyfraniad at gynhadledd › Papur

43. Cyhoeddwyd

    TEOS: A framework for constructing operational definitions of medication adherence based on Timelines – Events – Objectives – Sources

    Dima, A. L., Allemann, S. S., Dunbar-Jacobs, J., Hughes, D., Vrijens, B. & Wilson, I., Meh 2021, Yn: British Journal of Clinical Pharmacology. 87, 6, t. 2521-2533

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

44. Cyhoeddwyd

    Taxonomy for methods of resource use measurement

    DIRUM Team, 23 Ion 2015, Yn: Health Economics. 24, 3, t. 372-378

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Llythyr › adolygiad gan gymheiriaid

45. Cyhoeddwyd

    The British antibiotic and silver-impregnated catheters for ventriculoperitoneal shunts multi-centre randomised controlled trial (the BASICS trial): study protocol

    Hughes, D., Jenkinson, M. D., Gamble, C., Hartley, J. C., Hickey, H., Hughes, D. A., Blundell, M., Griffiths, M. J., Solomon, T. & Malluci, C. L., 3 Ion 2014, Yn: Trials. 15, 14

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

46. Cyhoeddwyd

    The Development of a Consistent Europe-Wide Approach to Investigating the Economic Impact of Myalgic Encephalomyelitis (ME/CFS): A Report from the European Network on ME/CFS (EUROMENE)

    Pheby, D. F. H., Araja, D., Berkis, U., Brenna, E., Cullinan, J., de Korwin, J-D., Gitto, L., Hughes, D., Hunter, R. M., Trépel, D. & Wang-Steverding, X., 7 Ebr 2020, Yn: Healthcare. 8, 2, 88.

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

47. Cyhoeddwyd

    The Population Pharmacokinetics of R and S-Warfarin: Effect of Genetic and Clinical Factors

    Hughes, D., Lane, S., Al-Zubiedi, S., Hatch, E., Matthews, I., Jorgensen, A. L., Deloukas, P., Daly, A. K., Aarons, L., Ogungbenro, K., Kamali, F., Hughes, D. A. & Pirmohamed, M., 1 Ion 2012, Yn: British Journal of Clinical Pharmacology. 73, 1, t. 66-76

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

48. Cyhoeddwyd

    The ROAM/EORTC-1308 trial: Radiation versus Observation following surgical resection of Atypical Meningioma: study protocol for a randomised controlled trial

    Jenkinson, M. D., Javadpour, M., Haylock, B. J., Young, B., Gillard, H., Vinten, J., Bulbeck, H., Das, K., Farrell, M., Looby, S., Hickey, H., Preusser, M., Mallucci, C. L., Hughes, D., Gamble, C. & Weber, D. C., 14 Tach 2015, Yn: Trials. 16

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

49. Cyhoeddwyd

    The SANAD II study of the effectiveness and cost-effectiveness of levetiracetam, zonisamide or lamotrigine for newly diagnosed focal epilepsy: an open-label, non-inferiority, multicentre, phase 4, randomised controlled trial

    Marson, A., Burnside, G., Appleton, R., Smith, D., Leach, J. P., Sills, G., Tudor-Smith, C., Plumpton, C., Hughes, D., Williamson, P., Baker, G. A., Balabanova, S., Taylor, C., Brown, R., Hindley, D., Howell, S., Maguire, M., Mohanraj, R. & Smith, P. E., 10 Ebr 2021, Yn: The Lancet. 397, 10282, t. 1363-1374

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid

50. Cyhoeddwyd

    The SANAD II study of the effectiveness and cost-effectiveness of valproate versus levetiracetam for newly diagnosed generalised and unclassifiable epilepsy: an open-label, non-inferiority, multicentre, phase 4, randomised controlled trial

    Marson, A., Burnside, G., Appleton, R., Leach, J. P., Sills, G., Tudor-Smith, C., Plumpton, C., Hughes, D., Williamson, P., Baker, G. A., Balabanova, S., Taylor, C., Brown, R., Hindley, D., Howell, S., Maguire, M., Mohanraj, R. & Smith, P. E., 10 Ebr 2021, Yn: The Lancet. 397, 10282, t. 1375-1386

    Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid