Summary of main findings
In this study, the one-year prevalence of dizziness in family practice in patients aged 65 or older was 8.3%. In general, the prevalence was higher in women than in men, and increased with age. However, the prevalence in the very old (≥ 85 years) was similar for men and women. The incidence of dizziness in family practice was 47.1 per 1000 person-years. The incidence rates of all subtypes except 'vertigo' increased with age. The incidence rate for the subtype 'vertigo' was higher in women than in men. The incidence rates for the subtypes 'presyncope' and 'disequilibrium' were similar for men and women in all age-groups. For about 40% of the patients the family physicians did not specify a diagnosis, and recorded a symptom diagnosis as the final diagnosis. Living alone, a lower level of education, pre-existing cerebrovascular disease, and pre-existing hypertension were independently associated with dizziness.
Strengths and limitations of this study
Although the majority of dizzy patients are seen in family practice, [12, 13] most prevalence studies on dizziness are community-based, and include a study population that is not representative of family practice. The present study is representative of family practice, has a large sample size, and uses the symptom(s) presented by the patient as a starting point.
A limitation of our study is its dependence on the quality of registration by the family physicians. It is possible that some family physicians incorrectly recorded a subsequent consultation as the first consultation for dizziness. This could have caused an overestimation of the incidence rates of dizziness. However, we consider such an overestimation to be limited, because all of the family physicians were trained to record episodes of care, and all episodes that were classified as a 'new episode of care' were checked twice for incorrect classification, both during the DNSGP-2 data-collection,  and during the present study. For one fourth of patients with a new episode of care the family physicians did not record the symptom(s) presented, but only an ICPC-based code for dizziness, so for this group of patients assignment to a dizziness subtype was not possible. Although this does not affect the prevalence rates, it causes an underestimation of the incidence rates for the different dizziness subtypes. It also implies a risk of selection bias: it is imaginable that some family physicians failed to record the symptom(s) presented by certain patients (for example patients with common, benign causes of dizziness). This can cause an underestimation of the contribution of this group of diagnoses to the subtypes of dizziness (Table 2).
Furthermore, we emphasize that Table 3 describes the diagnoses routinely recorded by the family physicians. However, it is not the yield of a standardized prospective diagnostic study.
The comparison of non-dizzy with dizzy patients (Table 4) also has some limitations. Firstly, although many factors are plausible, and have been found to be associated with dizziness in previous studies, we cannot determine a causal relationship because of the cross-sectional design of the study. Secondly, for some factors the percentage of missing values is high, especially with regard to level of education and medical history. Although the multivariate analysis showed no independent association for these missing values, a disturbing effect is possible. Thirdly, our definition of long-term drug use is merely an attempt to compensate for missing information about the duration of a prescription. However, the results are comparable to those of a Dutch polypharmacy study in family practice. Finally, the list of potential factors is not exhaustive, but a selection based on previous studies [2, 4, 6, 7, 22].
Comparison with existing literature
Compared to the results of another prevalence study on dizziness representative of primary care,  the prevalence rates we found were almost twice as high for all studied age-groups. This may be due to the studied population, because Sloane et al. included patients of family physicians, general practitioners, general internists, and general paediatricians. Kruschinski et al. also reported a lower prevalence. However, this may be due to the younger age of their study population (mean age 59 years), a different classification system (ICD-10 vs. ICPC), and a different method of data retrieval. In a longitudinal population-based study among people above 65 years, 11% of the participants reported dizziness problems, which is consistent with our study.
Previous prevalence studies carried out in a community-based population have reported much higher prevalence rates (15-50%) [1–6, 14–19]. This is probably due to the fact that complaints of dizziness do not automatically lead to a medical consultation.
Contrary to the findings of other studies, [1–3, 10, 11, 13] we found no gender differences with regard to prevalence and incidence rates in the oldest patients. This may be due to the fact that the relative contribution of gender-specific diagnoses, such as vestibular vertigo which is much more common in women,  decreases with age.
There are no previous studies on dizziness that have investigated the incidence of subtypes of dizziness in different age-groups. Our finding that the incidence rates of all dizziness subtypes increased with age, except for the subtype 'vertigo', may be due to the fact that the relative contribution of 'non-vestibular' causes of dizziness (such as cardiovascular conditions) increases with age.
In a community-based study, Neuhauser et al. reported an annual incidence of "dizziness/vertigo leading to a medical consultation" of 1.8%,  which may seem low compared to our study (annual incidence of 5%). However, this may be due to the younger age of the studied population (18-79 years), and a different research method (survey).
The family physicians recorded a symptom diagnosis as final diagnosis for 39% of the dizzy patients, i.e. no diagnosis could be made after opportunities for further confirmation (such as follow-up consultations, additional diagnostic tests, or a referral). Previous studies that have investigated causes of dizziness in primary care have reported varying percentages of dizziness with unknown cause, ranging from 0-5% [28, 29] to 22-37% [30–32].
Contrary to the findings of previous studies, [6, 22] in the present study living alone was found to be associated with dizziness. This association might be due to the fact that people who live alone are more likely to report dizziness, for example because they have fewer people to reassure them. An inverse association with level of education has been found in earlier studies, not only for patients with vestibular vertigo, but also for various health conditions that are not related to dizziness. The factors pre-existing cerebrovascular disease and hypertension have been investigated in several previous studies, but only reported to be associated with dizziness by Sloane et al [2, 4, 6, 22]. Previously reported associations with cataract,  diabetes, [2, 22] impaired hearing,  previous myocardial infarction, [2, 6, 22] polypharmacy, [6, 22] and psychiatric comorbidity could not be confirmed [4, 6, 7, 22]. However, these associations may be absent in our study because of the high percentage of missing values for the factor medical history.
Implications for future research
It would be worthwhile to perform a prospective cohort study that uses Drachman's classification as a starting point,  because the present study does not provide complete information about the incidence of each subtype of dizziness. Furthermore, the absence of gender differences in the incidence rates of the dizziness subtypes 'presyncope' and 'disequilibrium' needs to be confirmed in a new study. Finally, given the large proportion of undiagnosed dizzy patients in family practice, it would be worthwhile to carry out more diagnostic research on dizziness in a family practice setting. Although an increase in specific diagnoses does not necessarily imply an increase in specific therapies, such research may provide more 'diagnostic tools' for family physicians in daily clinical practice.