The response rates were 86% for cycle 1, 93.6% for cycle 2, 88.9% for cycle 3 and 84.8% for cycle 4. The response rate for cycle 1 was based on 20,095 participants selected to form the panel. For the other cycles, the response rates were based on 17,276 panel members. The attrition rates were 9.3% at the end of cycle 2, 6.7% in cycle 3 and 7.1% at the end of cycle 4. Complete response included participants who provided a complete response to the interview in each of the four cycles, or were deceased or institutionalized. A total of 13,582 participants (78.6%) had complete responses in all four cycles. The participants with partial or no responses were regarded as missing or incomplete. The present analysis included all of the 17,276 participants, regardless of the response pattern.
The mean age of 17,276 participants, stratified by sex and location for each cycle, is provided in . In general, female participants were significantly older than their male counterparts. Rural participants were older than urban participants. Stratification by sex and location showed that urban men were younger than rural and urban women, as well as rural men, in all four cycles. Rural men were older than urban men, and the opposite was observed in women ().
Weighted mean ± SE age (years) of men and women stratified by location (rural or urban) for each cycle
Weighted percentages of smoking status for each cycle were studied separately by location and sex (). The denominator of the percentage was the 1994/1995 target Canadian population of 28,318,308 people. The percentages of the respondents who did not provide an answer to the smoking questionnaire are also presented. The nonresponders to this question were those who were younger than 15 years of age and/or those who chose not to answer the question. The percentage of female nonsmokers was higher than male nonsmokers in all four cycles, and the percentage of both smokers and ex-smokers was higher in men than women. The number of smokers, ex-smokers and nonsmokers were higher in the urban population than in the rural population. The overall percentage of smokers decreased from 23.5% (cycle 1) to 18.3% (cycle 4), and the overall percentage of nonsmokers decreased from 32.9% (cycle 1) to 27.0% (cycle 4). The overall percentage of ex-smokers showed an increase from 23.9% (cycle 1) to 26.7% (cycle 4) ().
Weighted percentage of smoking status by location for each cycle (n=28,318,308)*
Participants stratified based on smoking status and cycle of participation
The prevalence of asthma based on the response to the question “Do you have asthma diagnosed by a health professional?” is provided in . Overall, asthma prevalence increased from 7.3% in cycle 1 to 7.5% in cycle 4, although the change was not statistically significant. Women showed an increase in asthma prevalence from 7.2% (cycle 1) to 8.1% (cycle 4), while men showed a decrease from 7.3% (cycle 1) to 6.9% (cycle 4) (). None of these changes in asthma prevalence from cycle 1 through cycle 4 were significant. Further stratification by sex and location showed an increase in asthma prevalence among rural and urban women, while the opposite was observed for rural and urban men (). Asthma was more prevalent in urban than rural residents. When stratified by location, rural men showed the most decline in asthma prevalence from cycle 1 to cycle 4, followed by urban men. However, both urban and rural women showed an increase in asthma prevalence over time ().
Prevalence of health professional-diagnosed asthma for each cycle stratified by sex and location
Figure 2) Overall asthma prevalence and prevalence stratified by sex. Prevalences are representative of the 1994/1995 population who reported that they had been diagnosed with asthma by a health professional. No significant differences were observed between asthma (more ...)
Figure 3) Asthma prevalence stratified by sex and location. Prevalences are representative of the 1994/1995 population who reported that they had been diagnosed with asthma by a health professional. No significant differences were observed between asthma prevalences (more ...)
Because no statistical difference was found in the overall prevalence, further analysis was conducted by stratifying by age groups (). Asthma prevalence was highest in urban men younger than 15 years of age compared with rural men, rural women and urban women. The prevalence of asthma was higher in urban men than rural men, and this difference was significant (P<0.05) in cycle 2 in the 15- to 34-year age group. A similar significant difference was noticed in women in cycle 2. In the same age group, asthma prevalence was observed to be higher in urban women than urban men, and this was significant in cycle 4 (P<0.05). In the 35- to 64-year age group, for all cycles, the prevalence of asthma was higher in women than men in both rural and urban locations. In the same age group, the prevalence of asthma among urban women increased significantly from 4.8% in cycle 1 to 8.1% in cycle 4 (P<0.05). When studying the differences between sexes, urban women showed a higher prevalence than urban men, and this was statistically significant in cycle 2. A similar trend was observed in rural men and women. For cycle 3, the prevalence in rural women was significantly higher than rural men (P<0.05). In the 65-year and older age group, asthma prevalence was higher in rural men (6.6% in cycle 1) and urban women (5.4% in cycle 1), and this, too, increased over time (7.7% in cycle 4 in rural men, and 7.8% in cycle 4 in urban women). However, the increase in prevalence over time was not significantly different.
Health professional-diagnosed asthma prevalence for each cycle stratified by age, sex and location
Asthma prevalence among smokers, ex-smokers and non-smokers is presented in . These results are based on NPHS participants who were older than 15 years of age. The prevalence of asthma stratified by smoking status was studied separately for sex and location. The rural and urban differences among smokers, ex-smokers and nonsmokers for cycle 1 through cycle 4 were not statistically significant. The prevalence of asthma was higher among urban smokers, ex-smokers and nonsmokers than among rural participants, except for during cycle 4, when asthma prevalence was higher among rural ex-smokers than among urban ex-smokers.
Physician-diagnosed asthma prevalence in smokers, ex-smokers and nonsmokers in each cycle stratified by sex and location
On studying asthma prevalence stratified by sex and smoking status, prevalence was higher in female smokers and ex-smokers than men in all four cycles. The difference in the prevalence among smokers was statistically significant at the P<0.05 level for all cycles except cycle 2. Among ex-smokers, the difference was significant only in cycle 3 and 4. The prevalence of asthma among nonsmokers was more prevalent in men than women; however, no statistical difference was observed.
Within the urban location category, the prevalence of asthma significantly increased from cycle 1 to cycle 4 (P<0.05) for all three smoking categories. The prevalence also increased for rural participants, but no statistical difference was found. Within sex, an increase in asthma prevalence among men and women was observed over time for all three smoking categories. The increase in prevalence from cycle 1 through cycle 4 was statistically significant for ex-smoking and nonsmoking women (P<0.001).