Which question would be appropriate for an observational study?

An observational study involves collecting data by observing phenomena in their natural setting without manipulating any variables. The question, "What types of rocks are found at a convergent boundary?" is best answered through such a study. A geologist would travel to a convergent boundary to observe, identify, and collect rock samples that have formed naturally. This method does not involve altering or controlling the geological processes. The other options propose questions that require controlled experiments where a variable is intentionally manipulated to observe its effect on another variable.

A: This requires an experiment where the variable (salt concentration) is manipulated to measure its effect on the rate of evaporation.

B: This requires an experiment where the variable (mass) is systematically changed to measure its effect on the gravitational field.

C: This requires an experiment where different materials (types of metal) are tested under controlled conditions to compare their conductivity.

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1. University of California Museum of Paleontology. (n.d.). Designing tests for your ideas. Understanding Science. Retrieved from https://undsci.berkeley.edu/article/000/howscienceworks07. This resource explains that scientists can test their ideas through both experiments and observational studies, noting that for many large-scale systems (like stars or geological formations), "the key to testing the hypothesis is to find a situation in which the relevant variables have occurred naturally." This directly applies to observing rock types at a plate boundary.

2. Johnson, C., Affolter, M. D., Inkenbrandt, P., & Mosher, C. (2017). An Introduction to Geology. OpenGeology. Salt Lake Community College. In Chapter 1, "The Scientific Method," the text describes how geologists use observation as a primary method for data collection. It states, "A geologist may make an observation in the field..." This aligns with the process of identifying rock types at a specific geological feature like a convergent boundary.

3. DiCenso, D. (2019). Observational Studies and Experiments. In Statistics Using Technology (3rd ed.). Section 1.4. This open-source textbook from a university press distinguishes between the two study types: "In an observational study, the researcher collects data without performing any experiments or applying any treatments... In an experiment, the researcher applies a treatment to the subjects and then observes the effects of the treatment." This definition classifies options A, B, and C as experiments and D as an observational study.