The Gross National Income (GNI) per capita can be used to assess the wealth or the developement of a country. According to the World Bank Development Indicators, the GNI per capita (Atlas Method) of Zimbabwe declined from 1100 US dollars in 1981 to 940 US dollars in 2016. That amounts of a 6.15 per cent decline on a yearly basis.
Obviously in some years the economy of Zimbabwe was able to experience some growth, but there were also long spells during which the economy kept contracting.
For instance in the 1997-2008 period, the GNI per capita grew only by 0.9 per cent in 2001 and contracted in all the other years. And in two years (2003, 2008) the economic decline was in double digit. See graph.
The economy was badly mismanaged, and in spite of all the good intentions that President Mugabe might have had to improve the quality of life for his fellow countrymen, he ended up doing a terrible job.