Effects of misclassification and temporal change of response in food frequency on risk ratio

The change in lifestyle data during 9 years: the reliability and continuity of baseline health practices

OBJECTIVES

To reveal change patterns in self-reported lifestyle data for 9 years, and examine the characteristics of changes by type of lifestyle and ageing.

METHODS

The authors used the lifestyle data of 7,080 male workers aged 20-59 who received checkups for 9 years. The proportions of change patterns during the 9 years were determined in seven health practices; smoking, eating breakfast, sleeping hours, working hours, physical exercise, eating nutritional balanced diets, and mental stress.

RESULTS

Among seven health practices, the keep rate of good health practice was highest for the non-smoking (90.8 %), followed by eating breakfast (69.0 %);and the lowest was physical exercise (13.7 %). The keep rate of poor health practice was highest for smoking (73.8 %), followed by non-physical exercise (67.1 %). The lowest rate of multiple changes during 10 years was smoking (7.1 %); the highest was mental stress (68.5 %).

CONCLUSIONS

As for the life style on smoking and eating breakfast seemed to be stable, using the data obtained at a specific point in time wouldn't much affect the results. On the contrary, for other life styles, they showed poor continuity during 9 years, so it would be necessary to take into consideration the time point of data collection.

Change in food intake frequency at five years after baseline in the JACC study

BACKGROUND

In a cohort study, information on an individual is taken at baseline, after which it usually remains fixed. There is some risk that this will lead to misclassification and cause weakened or biased results. To prevent such distortion, following up of exposure is important, although it is still scarce in practice.

METHODS

In the Japan Collaborative Cohort Study for Evaluation of Cancer Risk (JACC Study) sponsored by Monbusho (Ministry of Education, Science, Sports and Culture of Japan), 37,838 (14,531 males and 23,307 females) subjects out of a cohort of 127,477 inhabitants answered an interim questionnaire on food intake frequency consisting of 33 items about five years after registration. The long-term reproducibility was assessed using Spearman's correlation coefficients and agreement. From data at two time points, longitudinal change, age effect, and secular trend were examined. Subjective changes in these items at the time of the interim survey were also compared to longitudinal changes.

RESULTS

Spearman's correlation coefficients varied from 0.27 (fruit juice in males) to 0.55 (beef in females and milk in males), and agreement from 29.9% (fruit juice in males) to 61.4% (liver in females). Correlation was relatively stronger in meat and dairy products and weaker in vegetables and fruits. In both males and females, most increased food item was edible wild plants followed by confectioneries (males) and yogurt (females).

CONCLUSION

Over five years, food intake was considerably changed. These interim data could be used for a long-term follow-up study to prevent the results becoming weakened or biased.

Smoking and Drinking Habits Five Years after Baseline in the JACC Study

BACKGROUND

Observing longitudinal changes in smoking and drinking habits is important for evaluating the risk of incidence and death from cancer or other diseases in a cohort study.

METHODS

Smoking and drinking habits at baseline and about five years later among 18,312 males and 28,338 females were obtained from the baseline and interim surveys in the Japan Collaborative Cohort Study for Evaluation of Cancer Risk (JACC Study) sponsored by Monbusho (Ministry of Education, Science, Sports and Culture of Japan). Changes in smoking and drinking habits between the two surveys were observed. Odds ratios for quitting these habits at interim survey were estimated.

RESULTS

Percentages of current smokers at baseline and interim surveys were 51.0% and 45.5% in males, and 5.2% and 4.8% in females, respectively. Percentages of current drinkers at baseline and interim surveys were 78.0% and 73.2% in males, and 29.5% and 23.5% in females, respectively. The number of cigarettes per day among male current smokers and the usual amount of alcohol consumed on each occasion among current drinkers decreased between the two surveys. Odds ratios for smoking cessation increased with age at baseline and decreased with the number of cigarettes per day at baseline. Odds ratios for drinking cessation increased with age at baseline and decreased with the usual amount of alcohol consumed on each occasion at baseline.

CONCLUSION

The decrease in smoking and drinking habits was observed during the five-year follow-up period. Higher age and lower levels of exposure were associated with quitting smoking or drinking.