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12TABLE 2 Description of studies comparing results of randomised and non-randomised studies (cont’d)Conclusionabout bias(fromabstract)ConclusionaboutvariabilityConclusionabout casemixadjustmentSacks, 1982 27 Kunz, 1998, 28 Britton, 1998 25 MacLehose, Benson, 2000 32 Concato, 2000 33 Ioannidis, 2001 34 Lipsey, 1996, 352002 29 2000 26 2001 36Biases in patientselection mayirretrievablyweight theoutcome of HCTsin favour of newtherapiesOn average nonrandomisedstudiestend to result inlarger estimates oftreatment. It is notpossible to predictthe magnitude oreven direction ofpossible selectionbiases andconsequentdistortions oftreatment effectsResults of RCTs andnon-randomisedstudies do notinevitably differ; itmay be possible tominimise anydifferences byensuring thatsubjects included ineach type of studyare comparableQuasi-experimentaland observationalstudy estimates ofeffectiveness maybe valid if importantconfounding factorsare controlled forThere is littleevidence thatestimates oftreatment effects inobservationalstudies are eitherconsistently largeror qualitativelydifferent from thoseobtained inrandomisedcontrolled trialsThe results ofwell-designedobservationalstudies do notsystematicallyoverestimate themagnitude oftreatment ascompared withthose inrandomisedcontrolled trialsNo comment No comment No comment No comment No comment Observationalstudies had lessvariability in pointestimates thanRCTs of the sametopicAdjustment ofoutcomes in HCTsfor prognosticfactors did notappreciably changethe resultsNo commentDespite goodcorrelationbetweenrandomised trialsand nonrandomisedstudies– in particular,prospective studies– discrepanciesbeyond chance dooccur anddifferences inestimatedmagnitude oftreatment effect arevery commonBetween studyvariability is smalleramong RCTs thanprospective nonrandomisedstudies(p = 0.03) and allnon-RCTsNon-randomiseddesigns may yielddifferent observedeffects relative torandomiseddesigns, but thedifference is almostas likely torepresent anupward as adownward bias(from text)(p = 0.07)The effect ofadjustment forbaseline differencesbetween groups innon-randomisedstudies isinconsistentNo comment No comment No comment No comment No commentReview of empirical comparisons of the results of randomised and non-randomised studiesRR, risk ratio.
Health Technology Assessment 2003; Vol. 7: No. 27TABLE 3 Clinical topics investigated in each of the medical reviewsClinical topicSacks, 1982 27Kunz, 1998, 28 2002 29Britton, 1998 25MacLehose, 2000 26Concato, 2000 33Benson, 2000 32Ioannidis, 2001 341 Treatment of cirrhotic patients with oesophageal varicies ✓ ✓ ✓2 Surgical versus medical treatment of coronary artery disease ✓ ✓ ✓ ✓ ✓ ✓3 Anticoagulants for acute myocardial infarction ✓ ✓ ✓ ✓4 5-Fluorouracil adjuvant therapy for colon cancer ✓ ✓ ✓5 BCG adjuvant immunotherapy for malignant melanoma ✓ ✓ ✓6 Diethylstilbestrol for habitual abortion ✓ ✓ ✓7 Antiarrhythmic therapy for atrial fibrillation ✓ ✓ ✓ ✓8 Allogenic leucocyte immunotherapy for recurrent miscarriage ✓ ✓ ✓9 Oil soluble contrast media during hysterosalpingography for infertile couples ✓ ✓ ✓ ✓10 Hormonal therapy in cryptorchidism ✓ ✓ ✓11 TENS for postoperative pain ✓ ✓12 Matching of cancer control groups for six different cancers ✓13 β-Blockers for acute myocardial infarction ✓ ✓ ✓14 Surgical versus medical management of severe throat infections ✓ ✓15 Adenoidectomy for persistent otitis media ✓ ✓16 Chemotherapy, radiotherapy and tamoxifen in women with breast cancer ✓ ✓17 Treatment of benign oesophageal stricture ✓18 Day hospital versus inpatient care for alcoholism ✓19 Chorionic villus sampling versus early amniocentesis for karyotyping ✓ ✓20 Hospice versus conventional care for the terminally ill ✓21 Measles vaccine ✓22 Adjuvant doxorubin for treatment of sarcoma ✓23 Acute non-lymphatic leukaemia following adjuvant treatment for breast cancer ✓ ✓24 Antioxidant vitamins for cardiovascular protection ✓25 CABG vs PTCA for coronary artery disease ✓ ✓26 Calcium antagonists for acute coronary disease ✓ ✓27 Stroke units ✓28 Malaria vaccines ✓29 Breast conservation versus mastectomy for breast cancer ✓30 Tamoxifen versus placebo for breast cancer ✓31 Formula supplementation for infant feeding ✓32 Folic acid supplementation for prevention of neural tube defects ✓33 5-Fluorouracil adjuvant therapy for stomach cancer ✓34 Mammographic screening ✓ ✓ ✓35 BCG vaccine for prevention of tuberculosis ✓ ✓36 Treatment of cholesterol and death due to trauma ✓37 Treatment of hypertension and stroke ✓38 Treatment of hypertension and coronary heart disease ✓ ✓39 Intensive versus conventional insulin ✓40 Pneumatic retinopexy versus scleral buckling ✓41 Geriatric unit versus medical ward care (unclear for what condition) ✓42 Local versus general anaesthesia for endarcterectomy ✓ ✓43 Lithotripsy versus nephrolithotomy ✓44 Laser versus electrosurgical salpingostomy ✓45 Eder–Puestow versus balloon dilation ✓46 Hormone replacement therapy for osteoporosis ✓ a ✓47 Calcium channel blockers for renal graft survival ✓ a ✓48 Laparoscopic versus open appendectomy ✓ a ✓49 Naltrexone for alcohol dependence ✓50 Low-level laser therapy for osteoarthritis ✓51 Vaccine for meningitis serotype A ✓continued13© Queen’s Printer and Controller of HMSO 2003. All rights reserved.
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