Relative poverty measures look at the internal norms within a particular society or group. The gap between the wealthiest and the poorest in a society is precisely what relative poverty measures aim to identify. Studies based upon absolute poverty measures seem to indicate that absolute poverty is shrinking. Fukuda-Parr reports that "The correlation between income poverty and human poverty is weak, and there is a large spread in levels of human poverty among countries with similar levels of income poverty". Fukuda-Parr acknowledges that "The challenges of measuring human poverty are considerable, starting with the selection of key dimensions, their weighting, and a search for appropriate data sets". The absolute measures of poverty may be convenient for calculation and comparison, but they are not highly precise. Relative measures of poverty may be highly precise, but they are not terribly convenient for calculation or comparison.