A friend wants to explore age differences in happiness for her ph.d. thesis. she should most likely conduct a cross sectional study, because it will demand less time than the other types of study.
An observational research method known as a cross-sectional study examines data on variables that were gathered at one specific moment across a sample population or a pre-defined subgroup.
Cross-sectional analysis study can also be called transverse study, or prevalence study. Although cross-sectional research does not involve conducting experiments, researchers often use it to understand outcomes in the physical and social sciences and many business industries.
The answer is "this research would not require IRB review because it would be eligible for exemption since the researcher is not interacting with the children and the playground is a public setting".
IBR is a kind of board that applies research morals by looking into the techniques proposed for research to guarantee that they are moral and ethical and do not cross any limits proposed.