Statistical data can provide general information about how common a condition is, how many people have the condition, or how likely it is that a person will develop the condition. Statistics are not personalized, however—they offer estimates based on groups of people. By taking into account a person’s family history, medical history, and other factors, a genetics professional can help interpret what statistics mean for a particular patient.
Some statistical terms are commonly used when describing genetic conditions and other disorders. These terms include:
Common statistical terms
| Statistical term |
Description |
Examples |
| Incidence |
The incidence of a gene mutation or a genetic disorder is the number of people who are born with the mutation or disorder in a specified group per year. Incidence is often written in the form “1 in [a number]” or as a total number of live births. |
About 1 in 200,000 people in the United States are born with syndrome A each year. An estimated 15,000 infants with syndrome B were born last year worldwide. |
| Prevalence |
The prevalence of a gene mutation or a genetic disorder is the total number of people in a specified group at a given time who have the mutation or disorder. This term includes both newly diagnosed and pre-existing cases in people of any age. Prevalence is often written in the form “1 in [a number]” or as a total number of people who have a condition. |
Approximately 1 in 100,000 people in the United States have syndrome A at the present time. About 100,000 children worldwide currently have syndrome B. |
| Mortality |
Mortality is the number of deaths from a particular disorder occurring in a specified group per year. Mortality is usually expressed as a total number of deaths. |
An estimated 12,000 people worldwide died from syndrome C in 2002. |
| Lifetime risk |
Lifetime risk is the average risk of developing a particular disorder at some point during a lifetime. Lifetime risk is often written as a percentage or as “1 in [a number].” It is important to remember that the risk per year or per decade is much lower than the lifetime risk. In addition, other factors may increase or decrease a person’s risk as compared with the average. |
Approximately 1 percent of people in the United States develop disorder D during their lifetimes. The lifetime risk of developing disorder D is 1 in 100. |
For more information about understanding and interpreting statistics:
The New York Department of Health provides a basic explanation of statistical terms
, including incidence, prevalence, morbidity, and mortality.
Information about interpreting cancer statistics is available from the Centers for Disease Control and Prevention (CDC) as part of an educational module for students. Although this information focuses on cancer, information about health statistics can also apply to other disorders. The National Cancer Institute offers additional tools for understanding cancer statistics.
Next: How are genetic conditions and genes named?
