My background is anesthesiology and we live on data. Prior to surgery we look for any evidence, laboratory or symptomatic, that may give us clues as to the physical status of a person coming to surgery. We screen their medications, both prescribed and OTC, for potential interactions using databases such as Epocrates to assist us. During surgery, the individual variation in response to stimulation and medications becomes obvious, and data paves the way to perform the minute to minute changes required for a safe anesthetic. Though blood pressure, pulse and respirations are still key data, we can augment that information with hemoglobin oxygenation (O2 saturation), end-tidal carbon dioxide determinations, end-tidal anesthetic gas concentrations, respiratory pressures, neuromuscular blockade adequacy determinations, arterial blood gases, central venous pressures, transesophageal ultrasound ...
Data is what we, as physicians, depend on to provide competent diagnosis and care. However, when excessive, or poor quality data is used, it can be distracting or misleading. Likewise, over dependence on data can lead to poor quality care if the data used does not fully address the problem at hand. Both evidence and experience are important factors in using data well.