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Can we teach critical appraisal the GATE approach Rod Jackson University of Auckland, NZ September 2010 in 30 minutes!

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Presentation on theme: "Can we teach critical appraisal the GATE approach Rod Jackson University of Auckland, NZ September 2010 in 30 minutes!"— Presentation transcript:

1 Can we teach critical appraisal the GATE approach Rod Jackson University of Auckland, NZ September 2010 in 30 minutes!

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3 GATE: a Graphic Appraisal Tool for Epidemiology 1 picture, 2 formulas & 3 acronyms

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5 A picture: the GATE frame the shape of every epidemiological study ©

6 Participants Exposure GroupComparison Group Outcomes Time P E C O T The PECOT acronym: the 5 parts of every epidemiological study All epidemiological studies can be hung on the GATE frame

7 2 formulas: study analyses 1.Occurrence of disease = Numerator ÷ Denominator ÷ Time 2.Random error (95% Confidence Interval) = 1.96 x Standard Error D N

8 P EC O T PECOTPECOT Recruitment Allocation Maintenance Measurement of outcomes blind or objective The RAMMbo* acronym: assessing study bias * Paul Glasziou

9 Participants Exposure GroupComparison Group Outcomes Time P E C O T GATE frame picture & PECOT acronym Describe a studys design by hanging PECOT on the frame

10 Participants Study Setting Eligible Participants Participants P

11 Fill in for DVT in long-haul flights. Lancet 2001; 357: Page 95 in Glasziou et al

12 Participants Study Setting: volunteers, UK, ? 1990s Eligible Participants: no previous DVT, > 50 yrs, planned economy air travel 2 sectors > 8 hours Participants: 200, mean age years P DVT in long-haul flights: Lancet 2001;357:1485-9

13 Exposure & Comparison Groups Exposure or Intervention Group (EG) Comparison or Control Group (CG) EG CG

14 Fill in for DVT in long-haul flights. Lancet 2001; 357: Page 95 in Glasziou et al

15 Exposure & Comparison Groups Exposure or Intervention Group (EG): Below knee compression stockings Comparison or Control Group (CG): no stockings

16 Outcomes (O) O ab cd yes no Dis-ease

17 Fill in for DVT in long-haul flights. Lancet 2001; 357: Page 95 in Glasziou et al

18 Outcomes (O) O a= 0 b= 12 cd yes no DVT 100

19 Time (T) T incidence prevalence

20 Fill in for DVT in long-haul flights. Lancet 2001; 357: Page 95 in Glasziou et al

21 Time (T) T= from take-off to 2 days post final flight incidence Outcome: e.g. death 0

22 Time (T) T = at post-flight assessment (<48 hrs) prevalence Outcome: number with DVTs 0 12

23 Study design: GATE frame & PECOT Participants Exposure GroupComparison Group Outcomes Time P E C O T Every epidemiological study hangs on the GATE frame

24 Participants Exposure Group: stockings Comparison Group: no stockings Outcomes: DVT Time: at post flight assess DVT in long-haul flights: Lancet 2001;357: Setting: UK volunteers – 479 considered Eligible: > 50 yrs, no DVT, flying > 8 hrs 0 12

25 2 formulas: study analyses 1.Occurrence of disease = Numerator ÷ Denominator ÷ Time 2.Random error (95% Confidence Interval) = 1.96 x Standard Error D N

26 Denominator (Participants) D N Numerator (Outcomes) O = N÷D All epidemiological studies involve measuring the OCCURRENCE of disease Occurrence = Numerator ÷ Denominator

27 GATE study analyses P EG CG O Exposure Group (EG) Numerator 1: a Comparison Group (CG) Overall Denominator ab cd Numerator 2: b Describe a studys analyses by hanging the numbers on the frame Denominator 1:Denominator 2:

28 Occurrence = N ÷ D P EG CG O Denominator 1: Exposure Group EG Numerator 1: a Denominator 2: Comparison Group CG ab cd Numerator 2: b Exposure Group Occurrence: EGO = a ÷ EG Comparison Group Occurrence: CGO = b ÷ CG

29 Calculate EGO & CGO for the outcome DVT post long-haul flight P EG CG O ab cd Denominator 1: Exposure Group EG = 100 Numerator 1: a = 3* Denominator 2: Comparison Group CG = 100 Numerator 2: b = 12 EGO = 3/100 people at post flight assessment CGO = 12/100= people at post flight assessment * a = 0 but have used 3 to illustrate calculations on next slide

30 Describing differences between occurrences Relative difference or Relative Risk = EGO ÷ CGO Absolute Difference or Risk Difference = EGO - CGO Number Needed To Treat (NNT) = 1 ÷ RD

31 Fill in for DVT in long-haul flights. Lancet 2001; 357: Page 95 in Glasziou et al

32 Describing differences between occurrences Relative difference or Relative Risk = EGO ÷ CGO Absolute Difference or Risk Difference = EGO - CGO Number Needed To Treat (NNT) = 1 ÷ RD = 3/100 ÷ 12/100 = 3/12 = 0.25 = 3/ /100 = - 9/12 = /100 = 1 ÷ (- 7.5 /100) = - 100/7.5 = 13.3

33 Analyses its all about EGO & CGO

34 P EC O T PECOTPECOT Recruitment Allocation Maintenance Measurement of outcomes blind or objective The RAMMbo acronym: assessing study bias

35 R AMMbo E C O T appropriate Recruitment processes? P Study setting & eligibility criteria well described? e.g. Recruit random/representative sample OR consecutive eligibles OR volunteers from advertisements Participants representative of eligibles? Prognostic/risk profile appropriate to study question? P Study setting Eligible people

36 R AMMbo E C O T appropriate Recruitment processes? P Study setting & eligibility criteria well described? Recruited volunteers from advertisements; eligibility criteria well described Participants representative of eligibles? 479 considered, 248 excluded - probably Prognostic/risk profile appropriate to study question? yes P Study setting Eligible people

37 EG CG O T P RCT: Allocate randomly by investigators (e.g drugs) EG CG O T P Cohort: Allocate by measurement (e.g. smoking) R A MMbo: A is for Allocation were EG & CG similar at baseline?

38 EG CG O T P RCT: Allocate randomly by investigators using sealed envelopes R A MMbo: A is for Allocation EG & CG similar at baseline except more women in stocking group

39 RA M Mbo EG CG O T good Maintenance? did most participants remain in allocated groups (EG & CG) P Participants &/or investigators blind to exposure (and comparison exposure)? Compliance high & similar in EG & CG? Contamination low & similar in EG & CG? Co-interventions low & similar in EG & CG? Completeness of follow-up high & similar in EG & CG?

40 RA M Mbo 100 O T good Maintenance? did most participants remain in allocated groups (EG & CG) P Participants &/or investigators blind to exposure (and comparison exposure)? no Compliance high & similar in EG & CG? dk* Contamination low & similar in EG & CG? dk Co-interventions low & similar in EG & CG? dk Completeness of follow-up high & similar in EG & CG? probably ok, lost < 15% * dk = dont know

41 RAM Mbo EG CG O T Measurement of outcomes blind or objective? P If outcome measurements not Objective (eg. automated or definitive) were investigators blind to exposure (and comparison exposure)

42 RAM Mbo EG CG O T Measurement of outcomes blind or objective? P Outcome measurements reasonably objective (ultra-sound) Technician was blind to exposure (although some participants may have had a stocking line)

43 The 4 (GATE) study biases P E C O T Recruitment bias Allocation bias Maintenance bias Measurement (of outcomes) bias

44 P E C O T Recruitment ok Allocation ok Maintenance ok Measurement (of outcomes) ok DVT in long-haul flights: Lancet 2001;357:1485-9

45 2 formulas: study analyses 1.Occurrence of disease = Numerator ÷ Denominator ÷ Time 2.Random error (95% Confidence Interval) = 1.96 x Standard Error D N

46 2 formulas: study analyses 1.Occurrence of disease = Numerator ÷ Denominator ÷ Time 2.Random error (95% Confidence Interval) = 1.96 x Standard Error EGO = 0%; 95% CI = 0% - 3% CGO = 10%; 95% CI = 4.8% - 16% D N

47 Excel CATs & paper Gate-lites There is a GATE for every study design

48 the 3 rd acronym: SRs & meta-analyses F ind appropriate studies? A ppraise selected studies? I nclude only valid studies? T otal-up (synthesise) appropriately? H eterogeneity adequated addressed?

49 In the 19 th century we made great advances in health through the provision of clean, clear water; in the 21 st century we will make the same advances through clean, clear (systematically reviewed) information. Muir Gray Systematic reviews are one of the greatest ideas of modern thought. They should be celebrated. Ben Goldacre

50 Muhammad Shafique Sajid et al. Knee-length graduated compression stockings for thromboprophylaxis in air travellers: A meta-analysis. Int J Angiol. 2008; 17: 119–123. Nine trials studying participants using KL stockings were analyzed. Forty-six of 1261 participants randomly assigned to the control group developed deep vein thrombosis (DVT), compared with two of 1237 participants (0.16%) in the KL stockings group. …..There was an absolute difference of 3.4% in the incidence of DVT, in favour of KL stockings. The number needed to treat with KL stockings to avoid one case of DVT was However, there was significant heterogeneity among trials. The RR for DVT was 0.08 in high-risk participants and 0.14 in low- to medium-risk participants.

51 GATE can also be used to frame the first 4 steps of EBP

52 The 4 steps of EBP 1. Ask a focused question. 2. Access (systematically search for) epidemiological evidence to help answer question. 3. Appraise evidence found for its validity, effect size, precision (ideally all the relevant evidence) 4. Apply the evidence: a. amalgamate the valid evidence with other relevant information (patient/community values, clinical/health issues, & policy context) to make a good decision; and b. Act (implement) the decision in practice

53 Participants Exposure GroupComparison Group Outcomes Time P E C O T the PECOT acronym: the 5 parts of every epidemiological study All epidemiological studies can be hung on the GATE frame

54 EBP Step 1: ASK - turn your question into 5 parts (PECOT) 1.Participants (the patient problem) 2.Exposure (e.g. a therapy) 3.Comparison (there is always an alternative! - another therapy or no treatment… 4.Outcome (e.g. a disease you want to prevent or manage) 5.Time frame (over which you expect a result)

55 EBP Step 2: ACCESS the evidence – use PECOT to identify search terms 1.Participants (the patient problem) 2.Exposure (e.g. a therapy) 3.Comparison (there is always an alternative! - another therapy or no treatment… 4.Outcome (e.g. a disease you want to prevent or manage) 5.Time frame (over which you expect a result)

56 P EC O T PECOTPECOT Recruitment Allocation Maintenance Measurement of outcomes blind or objective EBP Step 3: APPRAISE the evidence – using PECOT & RAMMbo

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58 EBP Step 4: APPLY the evidence by: a. AMALGAMATING the relevant information & making an evidence-based decision: the X-factor ©

59 Epidemiologic evidence Clinical / health considerations Policy issues Patient / community preferences X-factor: making evidence-based decisions expertise: putting it all together the art of practice

60 Step 4b ACT

61 Step 5: EBP 360° 1.Ask a focused question. 2.Access (systematically search for) epidemiological evidence to help answer question. 3. Appraise evidence AND then meta-analyse (systematically review) ALL relevant valid evidence. 4. Apply the best evidence: a.amalgamate the valid evidence with other relevant information to make a good decision; and b.ACT on your decision 5. AUDIT your practice (i.e. check your actual practice – actions - against best evidence-based practice) = EBP + Quality Improvement

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