Final answer:
Loss to follow-up refers to participants who are no longer available for follow-up, while the health worker effect is the potential bias introduced by healthcare providers.
Step-by-step explanation:
Loss to follow-up refers to the situation when participants in a study or patients in a healthcare program are no longer available for follow-up or do not attend scheduled follow-up visits. This can occur for various reasons, such as moving away, loss of contact information, or lack of interest or motivation to continue with the program.
The health worker effect refers to the potential bias that can occur when healthcare providers or workers influence the outcomes being measured. For example, in a study on the effectiveness of a new treatment, if the healthcare providers are aware of which group of participants is receiving the new treatment, they may inadvertently provide additional support or care, leading to better outcomes for that group compared to the control group. This can make it difficult to accurately determine the true effectiveness of the treatment.