In a psychology experiment, what is the relationship between a hypothesis and an operational definition?

• A. A hypothesis is a vague guess; an operational definition is the study's conclusion.
• B. A hypothesis is a testable prediction about the relationship between variables; an operational definition specifies exactly how the variables will be measured or manipulated in the study.
• C. A hypothesis is only for qualitative data; operational definition is only for sampling.
• D. A hypothesis defines the sample; operational definition defines the population.

Answer: (D)

The key idea is turning ideas into something you can test and measure. A hypothesis is a testable prediction about how two or more variables relate to each other. It tells you what relationship you expect to find when you conduct the study and guides what data you’ll collect to test that prediction.

An operational definition moves from abstract ideas to concrete steps. It specifies exactly how you will measure or manipulate each variable in the study, so the idea is clear, replicable, and measurable. For example, if you think more sleep will improve memory, you would define sleep in a tangible way (hours slept last night, perhaps measured with a wearable device) and memory in a concrete way (score on a standardized memory test). The hypothesis tells you the expected relationship, and the operational definitions tell you how you’ll observe and test that relationship.

The notion that a hypothesis defines the sample or a population isn’t correct—the sample and population relate to who you study, while the operational definition relates to how you quantify or manipulate the variables in your experiment. The combination of a clear, testable prediction and precise, measurable definitions is what makes research reliable and interpretable.