Nghiên cứu bệnh chứng đồng nghĩa với nghiên cứu:

Nghiên cứu bệnh chứng dễ bị sai số chọn (selection bias) hơn so với các nghiên cứu quan sát khác như nghiên cứu thuần кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого кого 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

Nghiên cứu bệnh chứng dựa vào việc thu thập thông tin về tiền sử phơi nhiễm của những người mắc bệnh (nhóm bệnh) và những người không mắc bệnh (nhóm chứng). Vì vậy, những người tham gia nghiên cứu (đặc biệt là nhóm bệnh) thường phải nhớ lại những sự kiện, hành vi hoặc phơi nhiễm đã xảy ra trong quá khứ. Sai số nhớ lại (recall bias) xảy ra khi có sự khác biệt có hệ thống trong độ chính xác hoặc đầy đủ của thông tin được nhớ lại giữa các nhóm nghiên cứu. Trong nghiên cứu bệnh chứng, sai số này thường cao hơn so với các nghiên cứu quan sát khác do nhóm bệnh có xu hướng nhớ lại các phơi nhiễm có thể liên quan đến bệnh tật của họ nhiều hơn so với nhóm chứng.

Nghiên cứu bệnh chứng là một loại nghiên cứu quan sát hồi cứu. Trong nghiên cứu bệnh chứng, người ta bắt đầu với những người đã mắc bệnh (ca bệnh) và những người không mắc bệnh (chứng), sau đó xem xét lại quá khứ để tìm các yếu tố nguy cơ hoặc các yếu tố bảo vệ tiềm năng. Do đó, thời gian cần thiết để thực hiện nghiên cứu bệnh chứng thường ngắn hơn so với các nghiên cứu quan sát khác như nghiên cứu кого когорт (cohort study), đặc biệt là những когорт проспективны (prospective cohort study), vì nghiên cứu когорт theo dõi một nhóm người theo thời gian để xem ai phát triển bệnh và ai không.

Trong thử nghiệm ngẫu nhiên, đối tượng được chọn ngẫu nhiên từ quần thể nghiên cứu để tham gia vào các nhóm khác nhau (ví dụ: nhóm điều trị và nhóm chứng) được gọi là cá thể. Vì vậy, đáp án đúng là 'Cá thể'.

Phân loại nghiên cứu có thể dựa trên nhiều tiêu chí khác nhau. Trong các lựa chọn được đưa ra, "Theo thời gian" là một cách phân loại phổ biến (ví dụ: nghiên cứu cắt ngang, nghiên cứu dọc). Các cách phân loại khác có thể bao gồm theo mục tiêu nghiên cứu, phương pháp nghiên cứu, hoặc lĩnh vực nghiên cứu. Các lựa chọn khác như "Theo không gian", "Theo đặc trưng về con người" và "Theo loại mẫu sử dụng" có thể là các yếu tố được xem xét trong một nghiên cứu, nhưng chúng không phải là các cách phân loại nghiên cứu chính thống.