Question: What design? Analyze the design of each research example reported. Is it a sample survey, an observational study, or an experiment? If a sample, what are the population, the parameter of interest, and the sampling procedure? If an observational study, was it retrospective or prospective? If an experiment, describe the factors, treatments, randomization, response variable, and any blocking, matching, or blinding that may be present. In each, what kind of conclusions can be reached?
Researchers at the University of Bristol (England) investigated reasons why different species of birds begin to sing at different times in the morning. They captured and examined birds of 57 species at seven different sites. They measured the diameter of the birds' eyes and also recorded the time of day at which each species began to sing. These researchers reported a strong relationship between eye diameter and time of singing, saying that birds with bigger eyes tended to sing earlier. (Science News, 161, no. 16 [2002])