3. Identify which of the following parameters is being described below - your choices are (, , ₁ - ₂, ₁- ₂)

1. The difference in the population mean income between men and women
2. The difference in the population proportion who smoke between high school graduates and college graduates
3. The population proportion of Americans who think school guns should be carried on college campuses for their own protection.
4. The population average vitamin D levels in women over 60 in the US.