Methods for Specifying the Target Difference in a Randomised Controlled Trial: The Difference ELicitation in TriAls (DELTA) Systematic Review

English version České info

Background:
Randomised controlled trials (RCTs) are widely accepted as the preferred study design for evaluating healthcare interventions. When the sample size is determined, a (target) difference is typically specified that the RCT is designed to detect. This provides reassurance that the study will be informative, i.e., should such a difference exist, it is likely to be detected with the required statistical precision. The aim of this review was to identify potential methods for specifying the target difference in an RCT sample size calculation.

Methods and Findings:
A comprehensive systematic review of medical and non-medical literature was carried out for methods that could be used to specify the target difference for an RCT sample size calculation. The databases searched were MEDLINE, MEDLINE In-Process, EMBASE, the Cochrane Central Register of Controlled Trials, the Cochrane Methodology Register, PsycINFO, Science Citation Index, EconLit, the Education Resources Information Center (ERIC), and Scopus (for in-press publications); the search period was from 1966 or the earliest date covered, to between November 2010 and January 2011. Additionally, textbooks addressing the methodology of clinical trials and International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) tripartite guidelines for clinical trials were also consulted. A narrative synthesis of methods was produced. Studies that described a method that could be used for specifying an important and/or realistic difference were included. The search identified 11,485 potentially relevant articles from the databases searched. Of these, 1,434 were selected for full-text assessment, and a further nine were identified from other sources. Fifteen clinical trial textbooks and the ICH tripartite guidelines were also reviewed. In total, 777 studies were included, and within them, seven methods were identified—anchor, distribution, health economic, opinion-seeking, pilot study, review of the evidence base, and standardised effect size.

Conclusions:
A variety of methods are available that researchers can use for specifying the target difference in an RCT sample size calculation. Appropriate methods may vary depending on the aim (e.g., specifying an important difference versus a realistic difference), context (e.g., research question and availability of data), and underlying framework adopted (e.g., Bayesian versus conventional statistical approach). Guidance on the use of each method is given. No single method provides a perfect solution for all contexts.

Please see later in the article for the Editors' Summary

Vyšlo v časopise: Methods for Specifying the Target Difference in a Randomised Controlled Trial: The Difference ELicitation in TriAls (DELTA) Systematic Review. PLoS Med 11(5): e32767. doi:10.1371/journal.pmed.1001645
Kategorie: Research Article
prolekare.web.journal.doi_sk: https://doi.org/10.1371/journal.pmed.1001645

Souhrn

Zdroje

1. AltmanDG, SchulzKF, MoherD, EggerM, DavidoffF, et al. (2001) The revised CONSORT statement for reporting randomized trials: explanation and elaboration. Ann Intern Med 134: 663–694.

2. CopayAG, SubachBR, GlassmanSD, PollyJ, SchulerTC (2007) Understanding the minimum clinically important difference: a review of concepts and methods. Spine J 7: 541–546.

3. LenthRV (2001) Some practical guidelines for effective sample size determination. Am Stat 55: 187–193.

4. LenthRV (2001) “A first course in the design of experiments: a linear models approach” by Weber & Skillins: book review. Am Stat 55: 370.

5. WellsG, BeatonD, SheaB, BoersM, SimonL, et al. (2001) Minimal clinically important differences: review of methods. J Rheumatol 28: 406–412.

6. AletahaD, FunovitsJ, WardMM, SmolenJS, KvienTK (2009) Perception of improvement in patients with rheumatoid arthritis varies with disease activity levels at baseline. Arthritis Rheum 61: 313–320.

7. BarberBL, SantanelloNC, EpsteinRS (1996) Impact of the global on patient perceivable change in an asthma specific QOL questionnaire. Qual Life Res 5: 117–122.

8. BastyrEJIII, PriceKL, BrilV (2005) MBBQ Study Group (2005) Development and validity testing of the neuropathy total symptom score-6: questionnaire for the study of sensory symptoms of diabetic peripheral neuropathy. Clin Ther 27: 1278–1294.

9. BeninatoM, Gill-BodyKM, SallesS, StarkPC, Black-SchafferRM, et al. (2006) Determination of the minimal clinically important difference in the FIM instrument in patients with stroke. Arch Phys Med Rehabil 87: 32–39.

10. BrantR, SutherlandL, HilsdenR (1999) Examining the minimum important difference. Stat Med 18: 2593–2603.

11. DeRogatisLR, GraziottinA, BitzerJ, SchmittS, KoochakiPE, et al. (2009) Clinically relevant changes in sexual desire, satisfying sexual activity and personal distress as measured by the profile of female sexual function, sexual activity log, and personal distress scale in postmenopausal women with hypoactive sexual desire disorder. J Sex Med 6: 175–183.

12. DeyoRA, InuiTS (1984) Toward clinical applications of health status measures: sensitivity of scales to clinically important changes. Health Serv Res 19: 275–289.

13. EberleE, OttillingerB (1999) Clinically relevant change and clinically relevant difference in knee osteoarthritis. Osteoarthritis Cartilage 7: 502–503.

14. FritzJM, HebertJ, KoppenhaverS, ParentE (2009) Beyond minimally important change: defining a successful outcome of physical therapy for patients with low back pain. Spine 34: 2803–2809.

15. GlassmanSD, CopayAG, BervenSH, PollyDW, SubachBR, et al. (2008) Defining substantial clinical benefit following lumbar spine arthrodesis. J Bone Joint Surg Am 90: 1839–1847.

16. JaeschkeR, SingerJ, GuyattGH (1989) Measurement of health status. Ascertaining the minimal clinically important difference. Control Clin Trials 10: 407–415.

17. KawataAK, RevickiDA, ThakkarR, JiangP, KrauseS, et al. (2009) Flushing ASsessment Tool (FAST): psychometric properties of a new measure assessing flushing symptoms and clinical impact of niacin therapy. Clin Drug Investig 29: 215–229.

18. KhannaD, TsengCH, FurstDE, ClementsPJ, ElashoffR, et al. (2009) Minimally important differences in the Mahler's Transition Dyspnoea Index in a large randomized controlled trial—results from the Scleroderma Lung Study. Rheumatology (Oxford) 48: 1537–1540.

19. KragtJJ, NielsenIM, van der LindenFA, UitdehaagBM, PolmanCH (2006) How similar are commonly combined criteria for EDSS progression in multiple sclerosis? Mult Scler 12: 782–786.

20. KvammeMK, KristiansenIS, LieE, KvienTK (2010) Identification of cutpoints for acceptable health status and important improvement in patient-reported outcomes, in rheumatoid arthritis, psoriatic arthritis, and ankylosing spondylitis. J Rheumatol 37: 26–31.

21. MannionAF, PorchetF, KleinstückFS, LattigF, JeszenszkyD, et al. (2009) The quality of spine surgery from the patient's perspective: part 2. Minimal clinically important difference for improvement and deterioration as measured with the Core Outcome Measures Index. Eur Spine J 18 (Suppl 3)374–379.

22. MetzSM, WyrwichKW, BabuAN, KroenkeK, TierneyWM, et al. (2006) A comparison of traditional and Rasch cut points for assessing clinically important change in health-related quality of life among patients with asthma. Qual Life Res 15: 1639–1649.

23. PepinV, LavioletteL, BrouillardC, SewellL, SinghSJ, et al. (2011) Significance of changes in endurance shuttle walking performance. Thorax 66: 115–120.

24. PivaSR, GilAB, MooreCG, FitzgeraldGK (2009) Responsiveness of the activities of daily living scale of the knee outcome survey and numeric pain rating scale in patients with patellofemoral pain. J Rehabil Med 41: 129–135.

25. PopeJE, KhannaD, NorrieD, OuimetJM (2009) The minimally important difference for the health assessment questionnaire in rheumatoid arthritis clinical practice is smaller than in randomized controlled trials. J Rheumatol 36: 254–259.

26. PotterLP, MathiasSD, RautM, KianifardF, TavakkolA (2006) The OnyCOE-t questionnaire: responsiveness and clinical meaningfulness of a patient-reported outcomes questionnaire for toenail onychomycosis. Health Qual Life Outcome 4: 50.

27. PouchotJ, KheraniRB, BrantR, LacailleD, LehmanAJ, et al. (2008) Determination of the minimal clinically important difference for seven fatigue measures in rheumatoid arthritis. J Clin Epidemiol 61: 705–713.

28. RedelmeierDA, GuyattGH, GoldsteinRS (1996) Assessing the minimal important difference in symptoms: a comparison of two techniques. J Clin Epidemiol 49: 1215–1219.

29. RingashJ, BezjakA, O'SullivanB, RedelmeierDA (2004) Interpreting differences in quality of life: the FACT-H&N in laryngeal cancer patients. Qual Life Res 13: 725–733.

30. RingashJ, O'SullivanB, BezjakA, RedelmeierDA (2007) Interpreting clinically significant changes in patient-reported outcomes. Cancer 110: 196–202.

31. SantanelloNC, ZhangJ, SeidenbergB, ReissTF, BarberBL (1999) What are minimal important changes for asthma measures in a clinical trial? Eur Respir J 14: 23–27.

32. SekhonS, PopeJ (2010) Canadian Scleroderma Research Group, Baron M (2010) The minimally important difference in clinical practice for patient-centered outcomes including health assessment questionnaire, fatigue, pain, sleep, global visual analog scale, and SF-36 in scleroderma. J Rheumatol 37: 591–598.

33. SpiegelB, BolusR, HarrisLA, LucakS, NaliboffB, et al. (2009) Measuring irritable bowel syndrome patient-reported outcomes with an abdominal pain numeric rating scale. Aliment Pharmacol Ther 30: 1159–1170.

34. SunerIJ, KokameGT, YuE, WardJ, DolanC, et al. (2009) Responsiveness of NEI VFQ-25 to changes in visual acuity in neovascular AMD: validation studies from two phase 3 clinical trials. Invest Ophthalmol Vis Sci 50: 3629–3635.

35. TafazalSI, SellPJ (2006) Outcome scores in spinal surgery quantified: excellent, good, fair and poor in terms of patient-completed tools. Eur Spine J 15: 1653–1660.

36. TashjianRZ, DeloachJ, GreenA, PorucznikCA, PowellAP (2010) Minimal clinically important differences in ASES and simple shoulder test scores after nonoperative treatment of rotator cuff disease. J Bone Joint Surg Am 92: 296–303.

37. ten KloosterPM, Drossaers-BakkerKW, TaalE, van de LaarMA (2006) Patient-perceived satisfactory improvement (PPSI): interpreting meaningful change in pain from the patient's perspective. Pain 121: 151–157.

38. AbramsP, KelleherC, HuelsJ, Quebe-FehlingE, OmarMA, et al. (2008) Clinical relevance of health-related quality of life outcomes with darifenacin. BJU Int 102: 208–213.

39. AsenlofP, DenisonE, LindbergP (2006) Idiographic outcome analyses of the clinical significance of two interventions for patients with musculoskeletal pain. Behav Res Ther 44: 947–965.

40. BowersoxNW, SaundersSM, WojcikJV (2009) An evaluation of the utility of statistical versus clinical significance in determining improvement in alcohol and other drug (AOD) treatment in correctional settings. Alcohol Treat Q 27: 113–129.

41. BridgesTS, FarrarJD (1997) The influence of worm age, duration of exposure and endpoint selection on bioassay sensitivity for Neanthes arenaceodentata (Annelida: Polychaeta). Environ Toxicol Chem 16: 1650–1658.

42. DuruG, FantinoB (2008) The clinical relevance of changes in the Montgomery-Asberg Depression Rating Scale using the minimum clinically important difference approach. Curr Med Res Opin 24: 1329–1335.

43. FitzpatrickR, NorquistJM, JenkinsonC (2004) Distribution-based criteria for change in health-related quality of life in Parkinson's disease. J Clin Epidemiol 57: 40–44.

44. GnatR, KuszewskiM, KoczarR, DziewonskaA (2010) Reliability of the passive knee flexion and extension tests in healthy subjects. J Manipulative Physiol Ther 33: 659–665.

45. GrotleM, BroxJI, llestadNK (2006) Reliability, validity and responsiveness of the fear-avoidance beliefs questionnaire: methodological aspects of the Norwegian version. J Rehabil Med 38: 346–353.

46. HansonML, SandersonH, SolomonKR (2003) Variation, replication, and power analysis of Myriophyllum spp. microcosm toxicity data. Environ Toxicol Chem 22: 1318–1329.

47. JacobsonNS, TruaxP (1991) Clinical significance: a statistical approach to defining meaningful change in psychotherapy research. J Consult Clin Psychol 59: 12–19.

48. KendallPC, Marrs-GarciaA, NathSR, SheldrickRC (1999) Normative comparisons for the evaluation of clinical significance. J Consult Clin Psychol 67: 285–299.

49. KrebsEE, BairMJ, DamushTM, TuW, WuJ, et al. (2010) Comparative responsiveness of pain outcome measures among primary care patients with musculoskeletal pain. Med Care 48: 1007–1014.

50. ModiAC, ZellerMH (2008) Validation of a parent-proxy, obesity-specific quality-of-life measure: sizing them up. Obesity 16: 2624–2633.

51. MovsasB, ScottC, Watkins-BrunerD (2006) Pretreatment factors significantly influence quality of life in cancer patients: a Radiation Therapy Oncology Group (RTOG) analysis. Int J Radiat Oncol Biol Phys 65: 830–835.

52. NewnhamEA, HarwoodKE, PageAC (2007) Evaluating the clinical significance of responses by psychiatric inpatients to the mental health subscales of the SF-36. J Affect Disord 98: 91–97.

53. PekarikG, WolffCB (1996) Relationship of satisfaction to symptom change, follow-up adjustment, and clinical significance. Prof Psychol Res Pr 27: 202–208.

54. SarnaL, CooleyME, BrownJK, CherneckyC, ElashoffD, et al. (2008) Symptom severity 1 to 4 months after thoracotomy for lung cancer. Am J Crit Care 17: 455–467.

55. SeggarLB, LambertMJ, HansenNB (2002) Assessing clinical significance: application to the Beck Depression Inventory. Behav Ther 33: 253–269.

56. van der HoevenN (2008) Calculation of the minimum significant difference at the NOEC using a non-parametric test. Ecotoxicol Environ Saf 70: 61–66.

57. BacchettiP, McCullochCE, SegalMR (2008) Simple, defensible sample sizes based on cost efficiency. Biometrics 64: 577–585.

58. BriggsAH, GrayAM (1998) Power and sample size calculations for stochastic cost-effectiveness analysis. Med Decis Making 18: S81–S92.

59. DetskyAS (1990) Using cost-effectiveness analysis to improve the efficiency of allocating funds to clinical trials. Stat Med 9: 173–184.

60. GittinsJC, PezeshkH (2002) A decision theoretic approach to sample size determination in clinical trials. J Biopharm Stat 12: 535–551.

61. KikuchiT, PezeshkH, GittinsJ (2008) A Bayesian cost-benefit approach to the determination of sample size in clinical trials. Stat Med 27: 68–82.

62. O'HaganA, StevensJW (2001) Bayesian assessment of sample size for clinical trials of cost-effectiveness. Med Decis Making 21: 219–230.

63. SamsaGP, MatcharDB (2001) Have randomized controlled trials of neuroprotective drugs been underpowered? An illustration of three statistical principles. Stroke 32: 669–674.

64. TorgersonDJ, RyanM, RatcliffeJ (1995) Economics in sample size determination for clinical trials. QJM 88: 517–521.

65. WillanAR (2008) Optimal sample size determinations from an industry perspective based on the expected value of information. Clin Trials 5: 587–594.

66. AarabiM, SkinnerJ, PriceCE, JacksonPR (2008) Patients' acceptance of antihypertensive therapy to prevent cardiovascular disease: a comparison between South Asians and Caucasians in the United Kingdom. Eur J Prev Cardiol 15: 59–66.

67. AllisonDB, ElobeidMA, CopeMB, BrockDW, FaithMS, et al. (2010) Sample size in obesity trials: patient perspective versus current practice. Med Decis Making 30: 68–75.

68. BarrettB, BrownD, MundtM, BrownR (2005) Sufficiently important difference: expanding the framework of clinical significance. Med Decis Making 25: 250–261.

69. BarrettB, BrownR, MundtM, DyeL, AltJ, et al. (2005) Using benefit harm tradeoffs to estimate sufficiently important difference: the case of the common cold. Med Decis Making 25: 47–55.

70. BarrettB, HarahanB, BrownD, ZhangZ, BrownR (2007) Sufficiently important difference for common cold: severity reduction. Ann Fam Med 5: 216–223.

71. BellamyN, AnastassiadesTP, BuchananWW, DavisP, LeeP, et al. (1991) Rheumatoid arthritis antirheumatic drug trials. III. Setting the delta for clinical trials of antirheumatic drugs—results of a consensus development (Delphi) exercise. J Rheumatol 18: 1908–1915.

72. BellmLA, CunninghamG, DurnellL, EilersJ, EpsteinJB, et al. (2002) Defining clinically meaningful outcomes in the evaluation of new treatments for oral mucositis: oral mucositis patient provider advisory board. Cancer Invest 20: 793–800.

73. BloomLF, LapierreNM, WilsonKG, CurranD, DeForgeDA, et al. (2006) Concordance in goal setting between patients with multiple sclerosis and their rehabilitation team. Am J Phys Med Rehabil 85: 807–813.

74. BoersM, TugwellP (1993) OMERACT conference questionnaire results. OMERACT Committee. J Rheumatol 20: 552–554.

75. BurgessP, TrauerT, CoombsT, McKayR, PirkisJ (2009) What does ‘clinical significance’ mean in the context of the Health of the Nation Outcome Scales? Australas Psychiatry 17: 141–148.

76. FriedBJ, BoersM, BakerPR (1993) A method for achieving consensus on rheumatoid arthritis outcome measures: the OMERACT conference process. J Rheumatol 20: 548–551.

77. KirkbyHM, WilsonS, CalvertM, DraperH (2011) Using e-mail recruitment and an online questionnaire to establish effect size: a worked example. BMC Med Res Methodol 11: 89.

78. MoscaM, LockshinM, SchneiderM, LiangMH, AlbrechtJ, et al. (2007) Response criteria for cutaneous SLE in clincal trials. Clin Exp Rheumatol 25: 666–671.

79. RiderLG, GianniniEH, Harris-LoveM, JoeG, IsenbergD, et al. (2003) Defining clinical improvement in adult and juvenile myositis. J Rheumatol 30: 603–617.

80. StoneMA, InmanRD, WrightJG, MaetzelA (2004) Validation exercise of the Ankylosing Spondylitis Assessment Study (ASAS) group response criteria in ankylosing spondylitis patients treated with biologics. Arthritis Rheum 51: 316–320.

81. TubachF, RavaudP, BeatonD, BoersM, BombardierC, et al. (2007) Minimal clinically important improvement and patient acceptable symptom state for subjective outcome measures in rheumatic disorders. J Rheumatol 34: 1188–1193.

82. WellsG, AndersonJ, BoersM, FelsonD, HeibergT, et al. (2003) MCID/Low Disease Activity State Workshop: summary, recommendations, and research agenda. J Rheumatol 30: 1115–1118.

83. WongRK, GafniA, WhelanT, FranssenE, FungK (2002) Defining patient-based minimal clinically important effect sizes: a study in palliative radiotherapy for painful unresectable pelvic recurrences from rectal cancer. Int J Radiat Oncol Biol Phys 54: 661–669.

84. WyrwichKW, NelsonHS, TierneyWM, BabuAN, KroenkeK, et al. (2003) Clinically important differences in health-related quality of life for patients with asthma: an expert consensus panel report. Ann Allergy Asthma Immunol 91: 148–153.

85. WyrwichKW, FihnSD, TierneyWM, KroenkeK, BabuAN, et al. (2003) Clinically important changes in health-related quality of life for patients with chronic obstructive pulmonary disease: an expert consensus panel report. J Gen Intern Med 18: 196–202.

86. WyrwichKW, SpertusJA, KroenkeK, TierneyWM, BabuAN, et al. (2004) Clinically important differences in health status for patients with heart disease: an expert consensus panel report. Am Heart J 147: 615–622.

87. JohnstoneR, DonaghyM, MartinD (2002) A pilot study of a cognitive-behavioural therapy approach to physiotherapy, for acute low back pain patients, who show signs of developing chronic pain. Adv Physiother 4: 182–188.

88. KraemerHC, MintzJ, NodaA, TinklenbergJ, YesavageJA (2006) Caution regarding the use of pilot studies to guide power calculations for study proposals. Arch Gen Psychiatry 63: 484–489.

89. SalterGC, RomanM, BlandMJ, MacPhersonH (2006) Acupuncture for chronic neck pain: a pilot for a randomised controlled trial. BMC Musculoskelet Disord 7: 99.

90. ThabaneL, MaJ, ChuR, ChengJ, IsmailaA, et al. (2010) A tutorial on pilot studies: the what, why and how. BMC Med Res Methodol 10: 1.

91. BlumenauerB (2003) Quality of life in patients with rheumatoid arthritis: which drugs might make a difference? Pharmacoeconomics 21: 927–940.

92. BombardierC, HaydenJ, BeatonDE (2001) Minimal clinically important difference. Low back pain: outcome measures. J Rheumatol 28: 431–438.

93. CampbellJD, GriesKS, WatanabeJH, RaveloA, DmochowskiRR, et al. (2009) Treatment success for overactive bladder with urinary urge incontinence refractory to oral antimuscarinics: a review of published evidence. BMC Urol 9: 18.

94. CranneyA, WelchV, WellsG, AdachiJ, SheaB, et al. (2001) Discrimination of changes in osteoporosis outcomes. J Rheumatol 28: 413–421.

95. FeiseRJ, MenkeJM (2010) Functional Rating Index: literature review. Med Sci Monit 16: RA25–RA36.

96. MullerU, DuetzMS, RoederC, GreenoughCG (2004) Condition-specific outcome measures for low back pain: part I: validation. Eur Spine J 13: 301–313.

97. RevickiDA, FeenyD, HuntTL, ColeBF (2006) Analyzing oncology clinical trial data using the Q-TWiST method: clinical importance and sources for health state preference data. Qual Life Res 15: 411–423.

98. SchünemannHJ, GoldsteinR, MadorMJ, McKimD, StahlE, et al. (2005) A randomised trial to evaluate the self-administered standardised chronic respiratory questionnaire. Eur Respir J 25: 31–40.

99. JohnstonMF, HaysRD, HuiKK (2009) Evidence-based effect size estimation: an illustration using the case of acupuncture for cancer-related fatigue. BMC Complement Altern Med 9: 1.

100. Julious SA (2006) Designing clinical trials with uncertain estimates. London: University of London.

101. SuttonAJ, CooperNJ, JonesDR, LambertPC, ThompsonJR, et al. (2007) Evidence-based sample size calculations based upon updated meta-analysis. Stat Med 26: 2479–2500.

102. ThomasJR, LochbaumMR, LandersDM, HeC (1997) Planning significant and meaningful research in exercise science: estimating sample size. Res Q Exerc Sport 68: 33–43.

103. ZanenP, LammersJW (1995) Sample sizes for comparative inhaled corticosteroid trials with emphasis on showing therapeutic equivalence. Eur J Clin Pharmacol 48: 179–184.

104. AndrewMK, RockwoodK (2008) A five-point change in Modified Mini-Mental State Examination was clinically meaningful in community-dwelling elderly people. J Clin Epidemiol 61: 827–831.

105. ChinnS (2000) A simple method for converting an odds ratio to effect size for use in meta-analysis. Stat Med 19: 3127–3131.

106. Cohen J (1977) Statistical power: analysis of behavioural sciences. New York: Academic Press.

107. FredricksonA, SnyderPJ, CromerJ, ThomasE, LewisM, et al. (2008) The use of effect sizes to characterize the nature of cognitive change in psychopharmacological studies: an example with scopolamine. Hum Psychopharmacol 23: 425–436.

108. GordonJE, PowellC, RockwoodK (1999) Goal attainment scaling as a measure of clinically important change in nursing-home patients. Age Ageing 28: 275–281.

109. Hackshaw AK (2009) A concise guide to clinical trials. Oxford: Wiley-Blackwell.

110. HarrisMA, GrecoP, WysockiT, WhiteNH (2001) Family therapy with adolescents with diabetes: a litmus test for clinically meaningful change. Fam Syst Health 19: 159–168.

111. Higgins JPT, Greene S (2011) Cochrane handbook for systematic reviews of interventions, version 5.1.0. Available: http://www.cochrane-handbook.org/. Accessed 8 Apr 2014.

112. HortonAM (1980) Estimation of clinical significance: a brief note. Psychol Rep 47: 141–142.

113. HowardR, PhillipsP, JohnsonT, O'BrienJ, SheehanB, et al. (2011) Determining the minimum clinically important differences for outcomes in the DOMINO trial. Int J Geriatr Psychiatry 26: 812–817.

114. KlassenAF (2005) Quality of life of children with attention deficit hyperactivity disorder. Expert Rev Pharmacoecon Outcomes Res 5: 95–103.

115. KrakowB, MelendrezD, SisleyB, WarnerTD, KrakowJ, et al. (2006) Nasal dilator strip therapy for chronic sleep-maintenance insomnia and symptoms of sleep-disordered breathing: a randomized controlled trial. Sleep Breath 10: 16–28.

116. WoodsSW, StolarM, SernyakMJ, CharneyDS (2001) Consistency of atypical antipsychotic superiority to placebo in recent clinical trials. Biol Psychiatry 49: 64–70.

117. WyrwichK, HarnamN, RevickiDA, LocklearJC, SvedsäterH, et al. (2009) Assessing health-related quality of life in generalized anxiety disorder using the Quality Of Life Enjoyment and Satisfaction Questionnaire. Int Clin Psychopharmacol 24: 289–295.

118. ArbuckleRA, HumphreyL, VardevaK, ArondekarB, Danten-VialaM, et al. (2009) Psychometric evaluation of the Diabetes Symptom Checklist-Revised (DSC-R)—a measure of symptom distress. Value Health 12: 1168–1175.

119. FunkGF, KarnellLH, SmithRB, ChristensenAJ (2004) Clinical significance of health status assessment measures in head and neck cancer: what do quality-of-life scores mean? Arch Otolaryngol Head Neck Surg 130: 825–829.

120. CocksK, KingMT, VelikovaG, Martyn St-JamesM, FayersPM, et al. (2011) Evidence-based guidelines for determination of sample size and interpretation of the European Organisation for the Research and Treatment of Cancer Quality of Life Questionnaire Core 30. J Clin Oncol 29: 89–96.

121. Machin D, Day S, Greene S, editors (2006) Textbook of clinical trials. Chichester: John Wiley.

122. Cook JA, Hislop J, Altman DA, Briggs AH, Fayers PM, et al.. (2014) Use of methods for specifying the target difference in randomised controlled trial sample size calculations: two surveys of trialists' practice. Clin Trials. E-pub ahead of print. doi:10.1177/1740774514521907