More dogs are being diagnosed with thyroid problems than have been diagnosed in the past. A researcher identified 50 puppies without thyroid problems and kept records of their diets for several years to see if any developed thyroid problems. This is a(n) An Experiment An Observational Study A Simple Random Sample None of the above.

What the researcher is doing here is tracking the same group of puppies over time to see if any thyroid problems develop as they maintain their diets. This method resembles a classic observational study, where the researcher does not manipulate any variables but simply observes the outcomes based on natural differences in conditions. In terms of historical context, observational studies have deep roots in scientific research! One of the earliest examples dates back to the 19th century when John Snow used this approach to map out cholera cases in London. He observed the correlation between the water supply and the outbreak, leading to groundbreaking public health advancements!