Generally, the odor judge or panelist evaluates the odor by sniffing the exhaled air at a fixed distance (10 cm) from the subject’s mouth, and scoring the odor according to the scale (Fig. 8.1). This can be done directly from the subject’s mouth (e.g., during exhalation, speech – “count to 20”, blowing through a straw), or indirectly using a sampling bag. A partition screen is sometimes employed to blind the odor judge to the subject’s appearance (Murata et al. 2002).

In our initial studies, we adopted the ‘forced choice’ approach, i.e., the judge is forced to choose one of the 0–5 categories (Rosenberg et al. 1991a). But during the research, we sometimes faced dilemmas. How does one score the level of an odor that is somewhere between slight and moderate? One possibility was to use a visual analogue scale that is often used in perception studies, for example, to register the level of pain. In such instances, the judge has the option of drawing the line anywhere along the scale. We used this approach in one study, allowing the odor judge to score anywhere on a scale of 0 (no odor) to 10 (unbearably strong odor) (Goldberg et al. 1994). Since the scoring on such a scale is ostensibly linear and continuous, statistic analysis based on linear data can be more readily justified.

In subsequent studies, we used a similar approach. We went back to the six-point descriptive scale, but allowed judges to score at will in between the finite descriptors (e.g., give a score of 2.5, between slight and moderate) (Greenstein et al. 1997). When the sample size is large (e.g., n  =  100), the results approximate data obtained using a continuous scale. Analysis using statistical tools developed for studying continuous data (e.g., linear regression analysis, Pearson correlation coefficients) can then be employed with greater confidence.

Interpersonal variation in odor perception between odor judges still remains a major problem (Rosenberg et al. 1991b). In order to try and standardize odor judge scoring, calibration and training methods have been proposed. Odor judge training protocol based on the American Society of Testing and Materials Standards (introduction to sensory scales, use of n-butanol reference and sniffing techniques) was shown to reduce odor judge errors (Nachnani et al. 2005).

Dilution methods are usually device dependent. They are based on an apparatus or instrument designed to mix and dilute the odor sample to a set of concentrations enabling the judge to determine the minimal odor detectability or odor threshold. Some of these devices are handheld and used in field studies (e.g., olfactometer). In early studies on oral malodor done by Fosdick and colleagues, they reported the use of a device called the osmoscope as a sample dilution method designed to determine odor intensity (Brening et al. 1939).

Recently, a non-apparatus-dependent dilution method was reported (Bornstein et al. 2009). This method relies on the distance between the odor judge’s nose and the patient’s mouth as the diluting factor (i.e., 1 m, 30 and 10 cm) assuming that a higher intensity malodor would be sensed from a greater distance. Although organoleptic scales (continuous as possible) are more robust for research, this simple method was deemed suitable for a clinical setting.