In some countries, governments have detailed statistics based on the number of reported crimes per capita. While these surveys are usually particularly good for comparing crime between two cities within the same country, they may not be as suitable for cross-country comparisons due to the following reasons:
People in some countries are more likely to report a crime than in other countries.
Data could be forged by governmental institutions.
Data might not available in many parts of the world.
https://www.numbeo.com/crime/indices_explained.jsp
你呢個index既機構自己都講呢個index只適合比較同一個國家裏面嘅城市
因為
1. 喺某啲國家,當地人報案嘅意願可能比其他國家高
2. 政府機構可能會偽造數據
3. 世界各地好多地方都未必有呢啲數據