4.43 Mean versus median for age at first marriage: The mean age at first marriage was 31.1 years for men and 29.1 years for women in Canada in 2008 (open.canada.ca/en/open-data). The median age at first marriage was 28.9 years for men and 26.9 years for women in the United States in 2011 (https://data.census.gov/cedsci/table? q=United%20States%20age%20of%20first%20marriage%202011&tid=ACSDT1Y2011.B12007& hidePreview=false). Beyond the fact that these data are from slightly different years, explain why we cannot directly compare these measures of central tendency to make cross-national comparisons.