For some conditions (e.g. some types of cancer), starting treatment earlier can lead to better results.
The purpose of screening is to find the health condition so that treatment can be started as early as possible.
However, starting treatment early is not always beneficial and screening can result in overdiagnosis and have other side effects.
For example, screening for breast cancer with mammography can reduce the risk of dying from breast cancer in some women, but it also results in unnecessary treatment for some women.
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