Measures of Quality of Life
Several questionnaires are available to measure mood states or general quality of life, e.g. the Beck's Depression Inventory (BDI) ⁹², "mood" inventories ⁹³, or the Short Form-36 Health Survey (SF-36) ⁹⁴. These tests are known to be sensitive to changes in quality of life or mood states in different diseases ^{93, 95}. While these questionnaires allow the quantification of changes in the patients' quality of life in general, only recently questionnaires have been introduced which specifically addresses nasal or olfactory dysfunction, respectively (e.g., the Sinonasal Outcome Test-16 (SNOT 16) ⁹⁶).

The odor perception scale ⁹⁷ consists of three questions which allow the patient to indicate the degree of olfactory function. While this scale appears to be easy to use, it may not cover the full range of problems which is reported by patients with olfactory loss. In contrast, the "Questionnaire for Olfactory Dysfunction" (QOD) ⁷⁸ was developed in analogy to questionnaires used to quantify the degree of tinnitus ⁹⁸. The QOD consists of 52 statements, which can be divided into 3 domains: 39 "negative" statements, 5 "positive" statements, and 8 "socially desired" statements. The negative statements give information to which degree the patients suffer from the olfactory impairment. The positive statements indicate how well patients cope with their olfactory impairment; this relates to the fact that many dysosmic patients also report positive effects of their olfactory loss, e.g., they have little trouble changing diapers, sniff at vomit, or clean out unpleasantly smelling foods ⁵⁴. The "socially desired" statements - similar to the "lie scale" of the Eysenck Personality Inventory ⁹⁹ - are used to indicate the extent to which an individual is "honest", or whether he or she is trying to create a certain impression by providing socially desirable responses. In comparison to healthy subjects, based on results from the SD-36, patients suffering from olfactory dysfunction exhibited an impaired quality of life in several domains (e.g., "General Health Perception", and "Vitality"). When assessed with the QOD, hyposmic and anosmic patients' quality of life was found to be significantly impaired compared to patients with normosmia (compare ¹⁰⁰). Further, women seemed to suffer more from olfactory dysfunction than male patients. Additionally, when comparing patients with qualitative and quantitative olfactory dysfunction with those suffering from quantitative olfactory impairment only, the QOD was the only test to differentiate between those groups. In light of the difficulties to reliably quantify the degree of qualitative distortions through tests of olfactory function ³⁷, this seems to be of specific interest as therapeutic effects/changes over time are typically difficult to quantify in this group of patients. Overall, it appears as if the QOD was suited for the specific assessment of patients with olfactory dysfunction.

Another questionnaire has been described by the group around Lehrner ¹⁰⁰. The questionnaire is composed of twelve items. It consists of the 1-item subjective olfactory capability scale, the 5 item self-reported smell related problems scale, and 6-item olfactory related quality of life scale. All three scales significantly discriminate between healthy controls (n=128) and patients with anosmia (n=9). Single item group comparisons revealed that patients with smell loss indicated to be significantly impaired in areas of food, safety, personal hygiene, and additionally, in their sexual life (compare ^{54, 79}).

Varga, Breslin, and Cowart ¹⁰¹ presented a questionnaire to assess the impact of chemosensory dysfunction on every day life which also includes utility-based or time trade-off scales, with a particular focus on the value placed by patients on chemosensory function. In a sample of 105 patients with olfactory loss, increased concern was found regarding the ability to detect smoke, gas leaks, and spoiled food, which was related to measurable smell dysfunction. Up to one third of the patients rated their mood, ability to enjoy food, and social interactions as fair to poor. These ratings were associated with general depression scores. In fact, half of the patients reported to be willing to spend more than 20% of their annual household income to successfully treat chemosensory dysfunction.

Yet another questionnaire is the Multi-Clinic Smell and Taste Questionnaire for Scandinavian Use ¹⁰² which, apart from questions about chemosensory dysfunction and related medical history, includes questions about consequences of olfactory dysfunction. These latter questions refer to interference with daily routines and affected general well-being, life-quality, food appreciation and appetite. The vast majority of the questions have been demonstrated to be comprehensible and to generate responses with good reliability.

Using the Beck Depression Inventory ⁹² Deems and colleagues ¹⁰ reported that signs of depression were found in 29% of patients with chemosensory dysfunction (compare ^{54, 103}). This figure was slightly higher in patients reporting parosmia or parageusia (35%) compared to patients not reporting these symptoms (24%) ⁷⁸. However, remaining olfactory function does not seem to predict the loss of quality of life, as similar changes have been reported for anosmic and hyposmic patients. In addition, not all studies ¹¹ show a correlation between the patients' complaints and the measured ability to smell (but see also ^{55, 104}). In this context it is also interesting to note that persons with congenital anosmia do not indicate a restriction of their quality of life ¹¹. This is also supported by observations indicating that "congenital absence of olfaction does not result in markedly aberrant food preferences" ¹⁰⁵.

The different psychological tests used in the different investigations have been found to exhibit a high degree of correlation ^{78, 100}. The basis for this observation appears to be a state of general depression/impairment of quality of life, which is typcically seen in a large percentage of patients with olfactory dysfunction ^{10, 11, 76}. However, at least in patients with olfactory loss due to sino-nasal disease, a major component of the patients' decreased quality of life is related to the decreased patency of their nasal airways - which in turn will severely affect the results obtained by means of these questionnaires. In other words, at least in this group of patients, analysis of changes of the quality of life appears to be difficult, as olfactory and respiratory functions are so intimately linked to each other.