## **Core Concept**
The maternal and child welfare program involves monitoring and evaluation of health services provided to mothers and children. Sampling methods are crucial in such programs for assessing the effectiveness and coverage of these services. The **30 cluster sampling method** is specifically designed for evaluating programs in areas with limited resources and is commonly used in such public health initiatives.

## **Why the Correct Answer is Right**
The **30 cluster sampling method**, also known as the "30 clusters" technique, involves dividing the area to be surveyed into clusters, usually geographical, and then randomly selecting 30 of these clusters for detailed study. This method was originally developed by the World Health Organization (WHO) for assessing immunization coverage but has been applied more broadly in public health evaluations, including maternal and child health programs. It provides a rapid and cost-effective way to gather data on health service delivery and outcomes.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Simple random sampling involves selecting individuals or clusters from the population randomly, without any specific strategy like cluster sampling. While useful for some types of studies, it does not specifically address the structured, rapid assessment needs of large-scale public health programs like maternal and child welfare.
- **Option B:** Stratified sampling involves dividing the population into distinct subgroups (strata) and then sampling from each subgroup. While it ensures representation across subgroups, it may not provide the rapid, practical approach needed for evaluating service delivery across large areas.
- **Option C:** Systematic sampling involves selecting samples based on a fixed interval or system (e.g., every 10th item), which does not specifically cater to the cluster-based evaluation required for maternal and child health programs.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the **30 cluster sampling method** is particularly valuable in resource-limited settings or when rapid assessment is needed. It has been widely used in international health for evaluating the coverage and effectiveness of health programs, including vaccination campaigns and maternal and child health services.

## **Correct Answer:** D. 30 cluster sampling.