When something does not have a monetary value or is not tradable, its utility varies between different individuals and between different time periods

It is common sense that when there are more than enough choices available, it is harder to make the best decision. Based on the economics concept, we have to give a standard utility unit to all available choices' utilities in order to compare them "accurately", in other words numerically. My opinion is when something does not have a fixed monetary value or is not tradable, its utility always varies between different individuals and between different time periods. Once a good or a service has a monetary value and is tradable, it means all individuals can use the good or the service to exchange any other good or service with the same monetary value; therefore, the utilities of the tradable goods and services should be the same, if we ignore the transaction costs which always exist. However, if it does not have a fixed monetary value, it means that the goods or services it can be exchanged for are unfixed, so the utility of the good or the service is unfixed. Such goods can be art masterpieces, as people price them differently and their values can be different between generations. In addition, if the good or the service is untradable, then people cannot use it to exchange for other goods which may have the same monetary value, in this case the two goods' utilities are largely depending on individuals' preferences. Therefore, when something is not tradable in a free market (it is better to say in a perfectly competitive market, as individual actions will not have an impact on the market price), its utility is not fixed and is difficult to be compared with other goods and services.

The marginal utilities are generally considered to diminishing; therefore, the different levels of consumption will make the marginal utilities at that time point different from those at another time time point, when the individual cannot use a proportion of the consumption to exchange for something else. The different levels of consumption can be caused by different individuals' characteristics or different time periods. Individuals' personal preferences will give the same good or service with different utilities, unless they are tradable. Therefore, it is possible to rank the population's marginal utilities of the first consumption of an accountable number of goods and services. When the number of goods and services are included, the estimated ranking will be likely to be further away from the true ranking. In addition, when the consumption levels are high and different among the population, the estimated ranking will also be more likely to be further away from the true ranking, as the diminishing utility effects vary between different individuals.

Therefore, when we build a utility or preference model or function, it is better to have more objects with existing monetary values and have fewer objects without monetary values, and when each individual has a very different consumption level, it will cause the ranking that represents more of the majority consumption level group's preference rather than the natural utility of the good or service.