We noted that when comparing efficient outcomes, or points on the PPF, we cannot say which should be preferred. We also pointed out that if an outcome is inefficient, or under the PPF, all outcomes that contain more of both goods will be preferred, so long as both goods are actually "good" things.
What about a case such as that depicted graphically to the right? Point D is inefficient, but points A and C are both efficient outcomes since they lie on the PPF. Can we say that points A and C are better, or will always be preferred to D? All else being equal, efficient is better than inefficient, but all else isn't equal here. Point A offers 20 fewer units or about 33 percent less food than point D. It might be better for this society to tolerate some inefficiency than to have to cut its food consumption. Point C offers less housing than point D, so again, we cannot say that C will always be preferred to D. It may be that most societies would prefer either A or C to D, but the Production Possibilities graph does not provide enough information for us to know their preference.