How Can We Measure What Public Opinion Is?

In the physical world, you cannot have your unit of measurement. This makes it very complex to ask. So when we actually try to get what is called the latent construct, for example, happiness, we cannot directly access it. And so we access some other things which usually we access through different questions. The main thing is we need to ask these kinds of questions which are not exactly what we want to measure but they're linked to what we measure.