In biostatistics

Biostatistics

Biostatistics is the application of statistics to a wide range of topics in biology...

, survival rate is a part of survival analysis

Survival analysis

Survival analysis is a branch of statistics which deals with death in biological organisms and failure in mechanical systems. This topic is called reliability theory or reliability analysis in engineering, and duration analysis or duration modeling in economics or sociology...

, indicating the percentage of people in a study or treatment group who are alive for a given period of time after diagnosis. Survival rates are important for prognosis

Prognosis

Prognosis is a medical term to describe the likely outcome of an illness.When applied to large statistical populations, prognostic estimates can be very accurate: for example the statement "45% of patients with severe septic shock will die within 28 days" can be made with some confidence, because...

; for example, whether a type of cancer

Cancer

Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...

 has a good or bad prognosis can be determined from its survival rate.

Patient

Patient

A patient is any recipient of healthcare services. The patient is most often ill or injured and in need of treatment by a physician, advanced practice registered nurse, veterinarian, or other health care provider....

s with a certain disease

Disease

A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...

 can die directly from that disease or from an unrelated cause such as a car accident

Car accident

A traffic collision, also known as a traffic accident, motor vehicle collision, motor vehicle accident, car accident, automobile accident, Road Traffic Collision or car crash, occurs when a vehicle collides with another vehicle, pedestrian, animal, road debris, or other stationary obstruction,...

. When the precise cause of death

Cause of Death

Cause of Death is a 1990 album by American death metal band Obituary. Cause of Death is considered a classic album in the history of death metal. The artwork was done by artist Michael Whelan...

 is not specified, this is called the overall survival rate or observed survival rate. Doctors often use mean overall survival rates to estimate the patient's prognosis. This is often expressed over standard time periods, like one, five, and ten years. For example, prostate cancer

Prostate cancer

Prostate cancer is a form of cancer that develops in the prostate, a gland in the male reproductive system. Most prostate cancers are slow growing; however, there are cases of aggressive prostate cancers. The cancer cells may metastasize from the prostate to other parts of the body, particularly...

 has a much higher one year overall survival rate than pancreatic cancer

Pancreatic cancer

Pancreatic cancer refers to a malignant neoplasm of the pancreas. The most common type of pancreatic cancer, accounting for 95% of these tumors is adenocarcinoma, which arises within the exocrine component of the pancreas. A minority arises from the islet cells and is classified as a...

, and thus has a better prognosis.

Net survival rate

When someone is more interested in how survival is affected by the disease, there is also the net survival rate, which filters out the effect of mortality from other causes than the disease. The two main ways to calculate net survival are relative survival

Relative survival

When describing the survival experience of a group of people or patients typically the method of overall survival is used, and it presents estimates of the proportion of people or patients alive at a certain point in time...

and cause specific survival or disease specific survival.

• Relative survival is calculated by dividing the overall survival after diagnosis of a disease by the survival as observed in a similar population that was not diagnosed with that disease. A similar population is composed of individuals with at least age and gender similar to those diagnosed with the disease.

• Cause specific survival is calculated by treating deaths from other causes than the disease as withdrawals from the population that don't lower survival, comparable to patients who are not observed any longer, e.g. due to reaching the end of the study period.

Relative survival has the advantage that it does not depend on accuracy of the reported cause of death; cause specific survival has the advantage that it does not depend on the ability to find a similar population of people without the disease.

Related statistics

Overall survival is often used as an endpoint

End point of clinical trials

An endpoint is something which is measured in a clinical trial or study. Measuring the selected endpoints is the goal of a trial. The response rate and survival are examples of the endpoints....

 in clinical trial

Clinical trial

Clinical trials are a set of procedures in medical research and drug development that are conducted to allow safety and efficacy data to be collected for health interventions...

s, eg median overall survival expressed in months. (Median is used because it can be calculated once 50% of the subjects have died).