Katarina is interested in the relationship between attention deficit disorder and behavioral problems in school. she believes that children's socioeconomic status may affect her results, so she included two groups of children and made sure each child in one group came from a home with the same level of income as each child in the other group. what technique is this?

8) this map shows the population density of india. the redder the area, the higher the concentration of the population. which is the most likely reason for the high population density in the northeastern part of india? a) there is little pollution there b) the ganges river is in the region c) most of the factories are located in that region d) most people want to live close to the himalaya mountains