Final answer:
The correct answer is 'd. Twelve years of education', which refers to a specific measurable attribute and is a variable. Variables like this are crucial for statistical analyses in various studies to determine the relationship between an independent variable and a dependent variable.
Step-by-step explanation:
Among the options given, d. Twelve years of education corresponds to a property/variable. A variable is an attribute or characteristic that can take on different values or categories, and in this context, twelve years of education indicates a specific quantity of educational experience, which can be measured and used in statistical analysis. On the other hand, 'Education level' could be considered a broad category under which many specific variables (like 'twelve years of education') might fall. 'A highly educated person' and 'Educated people' are descriptions or categories that are more qualitative and encompass a range of possible education levels rather than precise variables.
Variables play a critical role in studies and surveys. For example, in a study analyzing the impact of education on crime rates, 'higher education (years)' would be considered an independent variable affecting the 'crime rates', the dependent variable. Similarly, when researching the pay gap, 'lower education level' might be an independent variable impacting the dependent variable of income.