Definitions for Childhood Cancer

Incidence rate -

We determine whether a disease is becoming more or less common by counting the number of new cases of the disease that are found in a group of people over a period of time - usually a year. This is often expressed as the number of cases per million people and often called the "incidence rate."

Case control studies -

In case-control studies of childhood cancer, researchers identify children who have been diagnosed with cancer.  These are called ‘cases.”  They also identify children who are similar except that they do not have the disease.  These are called “controls.”  Researchers then compared the exposures of the children who are cases to the children who are controls.  In a study of whether pesticides cause childhood cancer, for example, exposure to pesticides by either the parents or the child might be considered.  If significantly more cases than controls are exposed to a pesticide, for example, then that pesticide is considered to be a factor for the disease. 

The main weakness of this type of study for childhood cancer and pesticides is that exposures to pesticides are ascertained mostly by talking to the parents.  Those parents whose children are diagnosed with cancer may try harder to remember possible causes of the disease and consequently may remember pesticide use more fully than do other parents.  This is called “recall bias.”