Gallons of gasoline is not a construct, because we already have a way of measuring it in gallons. Intelligence is a construct. How do we measure and define intelligence? We have the IQ test, or maybe we could measure intelligence with grades. But grades may also help us measure something like how hard we’re working. Like effort. Effort is a construct. We might measure effort by how many minutes we spend working on homework or by grades, or GPA. Age is also a construct. If I had put age in years, I would have defined age as the number of years you’ve been living but some people might look at age as how mature you are. Here I didn’t put a way of measuring it, and age therefore is kind of tricky, would be considered a construct in this case. So maturity, age in years, and wisdom are all three different ways you could possibly measure age. Hunger is also a construct. Hunger could be measured by how often your tummy grumbles or by how deficient in nutrients your body is. Annual salary in US dollars, is not a construct. That’s because we put in US dollars. And therefore we have a way of measuring your annual salary. And finally itchiness is a construct. How would you define and measure itchiness? I’ll let you ponder that one yourself. We have to think carefully about how to define and measure constructs. The descriptions for constructs that we settle on, and that allow us to measure them, are called our operational definition.