Tài liệu NCKH (Chọn cỡ mẫu)

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Cỡ mẫu cho nghiên cứu phân tích

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<b>Nguy cơ tương đối =</b>

(1,8)

% phụ nữ ung thư vú có uống thuốc ngừa thai
% phụ nữ ko UTV , có uống thuốc ngừa thai

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n =

(mỗi nhóm)

Z

_1-α/2

√

2 P ( 1-P )

₀ ₀

₊

1-β

Z

√

P ( 1-P )

1 1

<b>+ </b>

P ( 1-P )

0 0

(P - P )

₁ ₀ 2

2

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• t-test, α in this equation is simply replaced by α/2
• n1= n2 , σ1= σ2 = .

ã Mean difference between the two populations : à1 µ2.
• The power = 0.8 or 80%.

• n = n1+ n2 = 45,2

CT cỡ mẫu /t-test

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