Change in the nationwide annual percent change (APC) before and after 2004.

AAPC (average APC): a weighted average of the APCs before and after 2004. P = 0.053 for difference in APC before and after 2004 by the Joinpoint regression analysis.</p

Summary of the secular trends in estimated participation rates (EPR) nationwide and by regional block.

APC: annual percent change. AAPC (average APC): a weighted average of the APCs before and after 2004. Nationwide-JP: nationwide Joinpoint regression curve with one joinpoint. See Fig 3 for details.</p

Nationwide and regional block-wise number of households per unit-district and members per household in Japan.

Nationwide and regional block-wise number of households per unit-district and members per household in Japan.</p

The data set underlying the results.

This study aimed to identify the trend of approximate participation rate in Japan’s National Health and Nutrition Survey (NHNS_J). The proportion of participants among all residents of surveyed districts (estimated participation rate: EPR) was calculated by 12 regional blocks, gender, and age group, and the trend and annual percent change (APC) were clarified. Based on the 1997–2019 NHNS_J data, we created a database classified by prefecture, gender, and age group; in addition to these, the number of people per household by Population Census or population estimates were obtained from e-Stat and added to the database. All analyses were performed by regional block and gender and EPR for each year was calculated by the age group. Trends of EPR, overall and by the age group, were presented using graphs, illustrating the exponential regression curve. The graphs showed APC, standard error, and statistical significance by age group. The EPRs were declining in all the regional blocks. Additionally, the rates of decline in APC in young people under the age of 50 years were higher than those in the older age groups in 9 of 12 regional blocks. The nationwide APC in the age group </div

Comparison of trends in estimated participation rates for age groups <50 years and ≥50 years for both sexes.

P = 0.001 for difference in annual percent change (APC) between the age groups. AAPC (average APC): a weighted average of the APCs before and after 2004. Nationwide-JP: nationwide Joinpoint regression curve with one joinpoint.</p

Survey districts and participants of NHNS_J.

The estimated participation rate (EPR) is defined as C/A.</p

Secular Trend of Estimated Participation Rate (EPR) (left) and Annual Percent Change (APC) (right) nationwide and by regional block, gender and age group.

Regional blocks: Hokkaido, Tohoku, Kanto I, Kanto II, Hokuriku, Tokai, Kinki I, Kinki II, Chugoku, Shikoku, Kita Kyushu, Minami Kyushu. See S1 Fig for geographic location.</p

Map of regional blocks and prefectures in Japan.

This study aimed to identify the trend of approximate participation rate in Japan’s National Health and Nutrition Survey (NHNS_J). The proportion of participants among all residents of surveyed districts (estimated participation rate: EPR) was calculated by 12 regional blocks, gender, and age group, and the trend and annual percent change (APC) were clarified. Based on the 1997–2019 NHNS_J data, we created a database classified by prefecture, gender, and age group; in addition to these, the number of people per household by Population Census or population estimates were obtained from e-Stat and added to the database. All analyses were performed by regional block and gender and EPR for each year was calculated by the age group. Trends of EPR, overall and by the age group, were presented using graphs, illustrating the exponential regression curve. The graphs showed APC, standard error, and statistical significance by age group. The EPRs were declining in all the regional blocks. Additionally, the rates of decline in APC in young people under the age of 50 years were higher than those in the older age groups in 9 of 12 regional blocks. The nationwide APC in the age group </div