Thiết kế nghiên cứu bệnh chứng sẽ thích hợp cho:

Thiết kế nghiên cứu bệnh chứng là loại nghiên cứu phân tích quan sát, trong đó chọn một nhóm người bệnh (case) và một nhóm người không bệnh (control), sau đó hồi cứu xem các yếu tố nguy cơ/bảo vệ nào đã xảy ra ở cả hai nhóm. Nghiên cứu bệnh chứng đặc biệt phù hợp khi nghiên cứu các bệnh hiếm gặp vì chúng ta có thể chủ động tìm kiếm những người mắc bệnh này. Các lựa chọn khác không phù hợp: nghiên cứu bệnh chứng không dùng để phát hiện bệnh sớm (mà là nghiên cứu sàng lọc), cũng không đặc biệt phù hợp với bệnh có ít dấu hiệu lâm sàng (cái này dùng nghiên cứu mô tả tốt hơn) hoặc thời gian tiềm ẩn dài (thích hợp cho nghiên cứu кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого 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кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого 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Công thức tính Odds Ratio (OR) trong nghiên cứu bệnh chứng là: OR = (a*d)/(b*c), trong đó:
a = Số người bệnh có tiếp xúc với yếu tố nguy cơ
b = Số người bệnh không tiếp xúc với yếu tố nguy cơ
c = Số người chứng có tiếp xúc với yếu tố nguy cơ
d = Số người chứng không tiếp xúc với yếu tố nguy cơ

Trong trường hợp này:
a = 117 (Số người bệnh có hút thuốc lá)
b = 150 (Số người bệnh không hút thuốc lá)
c = 94 (Số người chứng có hút thuốc lá)
d = 173 (Số người chứng không hút thuốc lá)

Vậy, OR = (117 * 173) / (150 * 94)
Phương án 4 là đáp án chính xác.

Trong nghiên cứu bệnh chứng, Odds Ratio (OR) được tính bằng công thức: (a*d)/(b*c), trong đó:
a = số người có bệnh và có phơi nhiễm (55)
d = số người không bệnh và không phơi nhiễm (173)
b = số người có bệnh nhưng không phơi nhiễm (84)
c = số người không bệnh nhưng có phơi nhiễm (94)

Vậy, OR = (55 * 173) / (94 * 84). Do đó, đáp án đúng là phương án 4.

Đây là bài toán về tổ hợp. Ta cần tính số cách chọn 3 phần tử từ 5 phần tử mà không quan tâm đến thứ tự. Công thức tổ hợp chập k của n là: C(n, k) = n! / (k! * (n-k)!)
Trong trường hợp này, n = 5 và k = 3, vậy số tổ hợp là: C(5, 3) = 5! / (3! * 2!) = (5 * 4 * 3 * 2 * 1) / ((3 * 2 * 1) * (2 * 1)) = (5 * 4) / (2 * 1) = 20 / 2 = 10. Vậy T = 10.