Answer:
Cross sectional research
Explanation:
Research is cross-sectional when it has to be performed on a given group that have common characteristics, and it is performed at the same time instance. It is used in developmental psychology to study the participants of different age interest at a given time. The characteristics of Cross-sectional research are;
Dr smith in our illustration chose participant from different ages, these participants have one thing in common which is the age. Also, Dr smith is carrying out this study same time by comparing the participant in the same age bracket, The study carried out by Dr Smith is cross-sectional research.