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Saudi Diploma in Family Medicine Center of Post Graduate Studies in Family Medicine

EBMEBMTherapy ArticlesTherapy Articles

Dr. Zekeriya Aktürkzekeriya.akturk@gmail.com

www.aile.net

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Case

You are seeing a 34 y/o woman with recurrent migraine headaches 3-4 times per month. All attempts to prevent them have had minimal success. She heard some vitamin supplement may help.

PICO:In women with frequent migraines unresponsive to usual therapies is there a vitamin that is more effective than placebo to decrease the frequency of migraine?

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1. Determine Relevance

Read the title and the conclusion of the abstract:

1. Did the authors study an outcome that patients would care about?

2. Is the problem studied one that is common to your practice and the intervention feasible?

3. Will this information, if true, require you to change your current practice?

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2. Determine Validity

• Internal validity: How well was the study done? Do the results reflect the truth?– Level of Evidence?

• External validity: can I apply these results to MY patients?

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2. Determine Validity

• Read the methods section

– Answer questions on lower half of worksheet

– Study design flaws are common, but are they

“fatal”?

• “Stop” questions = fatal flaws

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Fatal Flaw #1Was it a randomized controlled trial?

Randomization is the best protection against

being mislead

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Did investigators know to which group the potential subject would be assigned before enrolling them?

Fatal Flaw #2Was allocation assignment concealed?

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Are the study patients similar to yours?

• Addresses generalizability of results to your practice

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• Patients:– Type 1 diabetes, 13-39 years old– No Htn, chol, diabetic complications– Willing to check BS QID, inject insulin 3-4 times/day– Monthly visits for 6.5 years– Twice weekly phone follow-up x 6.5 years– Bajillion tests over 6.5 years

• Are these patients representative of type 2 diabetics seen in FP?– ADA uses these results to support tight glucose control in type 2

DMN Engl J Med 1993;329:977-986.

Diabetes Complications and Control Trial

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Were all the patients properly accounted for at its conclusion?

• Complete follow-up?

• “Intention to treat” analysis?

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Was study “double-blinded”?

• Did the patients know to which group they were assigned?

• Did the treating physician know?

• Did investigators assessing outcomes know?

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Were intervention and control groups similar?

• See Table 1 of most studies• Randomization is best way to avoid bias,

though imbalances still can occur (especially if allocation was not concealed)

• Small differences sometimes are important

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Significance of Results?

• Statistical – general standard: p-value < 0.05 (5%)

• Was the power adequate?– power = ability of the study to find a difference IF one truly exists

– general standard: power = 0.8• clinical vs. statistical significance

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Study results

Abbrev Variable Equation Value- subjects in control group - 250- subjects in experimental gr - 150- events in control group - 100- events in experimental group - 15CER control event rate = events / subjects in control gr 0.4, 40%EER experimental event rate = events / subjects in exp. group 0.1, 10%ARR absolute risk reduction = CER – EER 0.3, 30%RRR relative risk reduction = (CER - EER) / CER 0.75NNT number needed to treat = 1 / ARR 3.33RR relative risk = CER / EER 4

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Example A

• 10% of patients with disease A get complication if not treated

• If treated, complication decreases to 8%

• ARR=10-8=2%• RRR=2/10=20%• NNT=1/0.2=5 patients

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Example B

• 1.5% of patients with disease B get complication if not treated

• If treated, complication rate decreases to 0.9%

• ARR=1.5-0.9=0.6%• RRR=0.6/1.5=40%• NNT=1/0.006=167 patients