Income distribution is continuously being changed in the market economy as changes in underlying conditions bring forth adjustments in production. In each case, those who satisfy consumer demands more fully with their resources have higher incomes and those who do so less fully have lower incomes. Unless one looks at income distribution for everyone involved in the market, If one picks and chooses which persons to include in the calculation of income distribution, then one can render any result.
If there is a rich country isolated economically from a poor country and they integrate, then incomes for people in both countries will become more equal. If it’s legitimate to look at incomes in just one country in calculating the income distribution produced by some system, then it’s legitimate to look at incomes in just one province or one town or just between two persons. If the inequality of income in a system is to be calculated by taking a select group out of the whole, then it would be a simple matter to show extreme income inequality or perfect income equality in any system.