Donald is studying the eating habits of all students attending his school. He samples the population by dividing the students into groups by grade level and randomly selecting a proportionate number of students from each group. He then collects data from the sample. Which type of sampling is used? Cluster sampling Stratified sampling Systematic sampling Convenience sampling

Donald is using stratified sampling because he divides the students into groups (strata) based on their grade levels and then selects a proportionate number of participants from each group. This method ensures that each grade is fairly represented in the sample, allowing for more accurate insights into the eating habits across different grades. To further explore sampling methods in research, it's interesting to note that stratified sampling can help reduce variability and improve the reliability of the results, especially in heterogeneous populations. For instance, in studying students, if one grade tends to have different eating habits compared to others, this method ensures that those differences are captured and analyzed effectively.