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Statistical Statistical VariablesVariables
Supervisied by:Supervisied by:Professor Samer Roustom, Professor Samer Roustom,
M.D.M.D.Sara Oubari & Laila NourSara Oubari & Laila Nour
Statistical Statistical VariablesVariables
If Epidemiology is about understanding the world in terms of RatiosStatistics is about understanding the world in terms of Distributions
Interferential Statistics bulids a bridge between the sample and the
population
Interferential Statistics bulids a bridge between the sample and the
population
instead of proving our hypothesis, we just try to prove that all of the
alternatives are wrong
Patients with elevated plasma creatinine or Patients with elevated plasma creatinine or
RRT had an annual death rate of 19.2% RRT had an annual death rate of 19.2% (95% (95% confidence interval, CI, 14.0 to 24.4%). confidence interval, CI, 14.0 to 24.4%). There There
was a trend for increasing risk of was a trend for increasing risk of cardiovascular death with increasing cardiovascular death with increasing
nephropathy nephropathy (P < 0.0001)(P < 0.0001)
Absolute risk
Relative risk (RR)
Cohort studies
Relative risk (RR)• RR = 1 No difference in risk
• RR < 1 Exposed < Unexposed
• RR > 1 Unexposed < Exposed
• Relative risk reduction
Odds Ratio(OR)
Case-Control studies
Smoking Lung Cancer TotalYes No
Yes 30 170 200No 5 995 1000
Total 35 1165 1200
Risk for smokers = 30/200 = 0.15Risk for nonsmokers = 5/1000 = 0.005Relative risk (RR) = 0.15/0.005 = 30
Odds for smokers = 30/170 = 0.176 Odds for nonsmokers = 5/995 = 0.005 Odds ratio (OR) = 0.176/0.005 = 35.1
Flavonol V.S CHDComparison of individuals in the top third with
those in the bottom third of dietary flavonol intake yielded a combined risk ratio of 0.80 (95% CI 0.69–0.93) after adjustment for known CHD risk factors
and other dietary components.
Maternal dietary supplements and language delayAdjusted ORs for 3 patterns of exposure to maternal dietary supplements were (1) other supplements, but no folic acid (n = 2480 [6.6%], with severe
language delay in 22 children [0.9%]; OR, 1.04; 95% CI, 0.62-1.74); (2) folic acid only (n = 7127 [18.9%], with severe language delay in 28 children
[0.4%]; OR, 0.55; 95% CI, 0.35-0.86); and (3) folic acid in combination with other supplements (n = 19 005 [50.5%], with severe language delay in 73
children [0.4%]; OR, 0.55; 95% CI, 0.39-0.78).