Step 1: Understanding the Question.
We are asked to pick the one item, out of four, that does NOT count as a socio-economic indicator.
Step 2: Key Concept.
Socio-economic indicators describe a population's living conditions and social standing, such as education, income, and housing. Health indicators, on the other hand, describe how well people's bodies and health status are doing, and life expectancy belongs to that second group.
Step 3: Detailed Explanation.
Literacy rate reflects the level of education in a community and is a well accepted socio-economic indicator.
Family size relates to household structure and living standards, and is used as a socio-economic marker, since smaller families are usually linked with better socio-economic status.
Housing quality directly measures living conditions, so it is also a core socio-economic indicator.
Life expectancy at birth, the average number of years a newborn is expected to live, is classified as a health status indicator. It is influenced by socio-economic factors, but it measures health outcomes, not social or economic standing directly.
Step 4: Final Answer.
Since life expectancy at birth belongs to the health indicators group rather than the socio-economic group, it is the one that is NOT a socio-economic indicator.