Định nghĩa DTH của J.N. Morris(1975):” DTH là khoa học ......... của y học dự phòng và y tế công cộng.”

Dự phòng cấp một (Primary Prevention) nhằm mục đích ngăn ngừa bệnh tật xảy ra ngay từ đầu. Để đo lường hiệu quả của dự phòng cấp một, ta cần xem xét số lượng ca bệnh mới xuất hiện trong một khoảng thời gian nhất định. Tỷ lệ mới mắc (incidence rate) là thước đo phù hợp để đánh giá điều này, vì nó cho biết tần suất xuất hiện các ca bệnh mới trong một quần thể trong một khoảng thời gian nhất định. Tỷ lệ hiện mắc (prevalence rate) cho biết tổng số ca bệnh (cả cũ và mới) tại một thời điểm, do đó không phù hợp để đo lường hiệu quả của các biện pháp dự phòng làm giảm sự xuất hiện của các ca bệnh mới.

Thời gian phát triển trung bình của bệnh không liên quan trực tiếp đến hiệu quả của dự phòng cấp một.

Như vậy, đáp án đúng là tỷ lệ mới mắc.

Tỷ lệ chết thô chịu ảnh hưởng lớn bởi cơ cấu tuổi của dân số. Các nước phát triển thường có tuổi thọ cao hơn và tỷ lệ người già trong dân số lớn hơn so với các nước đang phát triển hoặc kém phát triển. Do đó, ngay cả khi điều kiện sống và chăm sóc sức khỏe tốt hơn, tỷ lệ chết thô vẫn có thể cao hơn ở các nước phát triển vì nhóm người cao tuổi, những người có nguy cơ tử vong cao hơn, chiếm tỷ lệ lớn trong dân số. Trong trường hợp này, quần thể người Hoa Kỳ già hơn quần thể người Guyana, dẫn đến tỷ lệ chết thô cao hơn, mặc dù Hoa Kỳ là một nước phát triển hơn.

Trong định nghĩa về dịch tễ học, "dịch" được xác định khi có sự gia tăng đáng kể về số lượng ca bệnh so với mức bình thường được ghi nhận tại một địa phương cụ thể trong một khoảng thời gian ngắn. Do đó, từ thích hợp nhất để điền vào chỗ trống là "Tỷ lệ", vì nó thể hiện sự so sánh số lượng ca bệnh thực tế so với số lượng dự kiến hoặc trung bình. Các lựa chọn khác không phù hợp vì "Số" chỉ đơn thuần là số lượng, "Tần số" đề cập đến số lần xuất hiện, và "Tỷ số" là một khái niệm toán học khác.

Câu hỏi đề cập đến trường hợp kết quả xét nghiệm chưa đủ để đưa ra quyết định điều trị. Điều này thường xảy ra với các test phát hiện bệnh (screening test) hoặc test có độ nhạy cao. Các test này thường được sử dụng để sàng lọc ban đầu và cần được xác nhận bằng các test chẩn đoán có độ đặc hiệu cao hơn trước khi tiến hành điều trị. Trong các lựa chọn đưa ra, "Test phát hiện bệnh" phù hợp nhất vì nó chỉ ra rằng cần có các xét nghiệm khác (thường là test chẩn đoán) để xác nhận trước khi điều trị.

Nghiên cứu dịch tễ học phân tích được sử dụng để kiểm tra các giả thuyết về mối quan hệ nhân quả giữa các yếu tố nguy cơ và bệnh tật. Nghiên cứu mô tả chỉ đơn thuần mô tả sự phân bố bệnh tật, trong khi nghiên cứu thực nghiệm can thiệp để thay đổi một yếu tố và quan sát kết quả. Nghiên cứu tương lai không phải là một loại nghiên cứu dịch tễ học cụ thể, mà là một hướng tiếp cận (ví dụ, 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 кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого 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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