Evidence, broadly construed, is anything presented in support of an assertion. This support may be strong or weak. The strongest type of evidence is that which provides direct proof of the truth of an assertion. The evidence is contradictory on how built form affects people's lives. Making places is expensive, and people search for evidence to support design decisions to ensure that what they build will effectively meet their needs and goals. Environmental design research ranges from rigorous social science studies, focusing on a single feature like a view or daylighting, to more prompt and practical investigations, often integrating many features. Observing people in places, watching a transplant operation by video, joining a family in preparing a meal, or tracking a factory worker throughout a day gives designers useful information. Direct observation of how people use places needs to take into account how observers may affect the outcome.