:: IJEEIT :: (International Journal of Electrical Engineering and Information Technology) Volume 04 Number 01 March 2021 This work is licensed under a Creative Commons Attribution- ShareAlike 4.0 International License. ISSN : 2615-2096 (ONLINE) ISSN : 2615-2088 (PRINTED) 23 Early Detection of Diseases And Abnormalities In The Respiratory System Using Certainty Factor Method Mohammad Arman Prambudi 1 , Achmad Muchayan 2 Faculty of Computer Science, Narotama University, Indonesia armanprambudi02@gmail.com ABSTRACT Health is a very important factor in the human body. If the health of ourselves is interrupted, it is also interrupted by someone to do the activity. There are several diseases that have a lot of sufferers. One of them is the disease of the respiratory system. Respiratory system is defined generally as a matter that disrupts the process of breathing in our body. Diseases of the respiratory system is one of the main problems of public health in Indonesia, because the disease is a human breathing. The expert system is a library of specialists or an expert in diseases of the respiratory system and the conditions used to take the conclusion of the symptoms. In the calculation process used the certanity factor method to find a percentage level of confidence. The Parameter used in the diagnosis is the symptom chosen by the sufferer. The conclusion of this application results in the diagnosis of the disease suffered and the percentage result of confidence through the selected symptoms. Keywords: Respiratory disease, expert system, Certainty Factor 1. INTRODUCTION If observed daily life in society, apparently not only educational, economic, and cultural factors are a big problem for society today. Social & health factors are also a much more important problem to note because the welfare of life has a huge impact on the level of health in the community itself. Health is a valuable thing for people because anyone can experience health problems. In general our body is very susceptible to germs & viruses. People are also usually less sensitive to the symptoms of a disease. Limited public knowledge of diseases that attack the respiratory system becomes a problem and makes it difficult for people to predict the disease suffered. In this case the community needs a doctor / expert who can help to diagnose early so that it can take precautions early. To overcome this, a tool is needed that can diagnose a disease in the form of an expert system. Expert system is a software or computer program that is intended as a provider of advice and tools to help solve problems in certain areas of specialization such as science, mathematical engineering, medicine, education and so on (Turban, E. Aronson and Liang, 2007). The basis of an expert system yairu how to trust the science of an expert / expert into the computer / system and how to make decisions from that knowledge(Gustina and Chandra, 2015). The solution to the problem is to create an application to diagnose the disease based on the symptoms suffered. Starting from the problem, in this study will make an expert system that is able to diagnose diseases and abnormalities of the respiratory system by looking at the symptoms experienced by a person. This expert system is also useful to help the public to know, understand how much certainty is affected by respiratory system diseases. This expert system application can also find out the treatment of first aid in someone who is experiencing the disease. The expert system that will be created in this study uses the Certainty Factor method to determine the certainty value of the disease by calculating the weight value of symptoms in the disease. Expert systems will be made based on Android, because nowadays people are familiar with smartphones, almost everyone has smartphones ranging from children to adults and smartphones are very often used to find information rather than using a PC or laptop. The system will produce output in the form of a diagnosis of a disease experienced by a person, symptoms that have been selected by the user, and provide solutions for how to prevent disease first aid disease based on the input symptoms that are brought. logged out by the user. There are several related studies on expert systems to diagnose diseases of the respiratory system and with different solutions. Among them was research conducted by Nur Aini, Ramadiani, Heliza Rahmania Hatta in 2017. This research built an expert system that specifically identifies tuberculosis. In this system will receive