Anti-doping agencies monitor professional athletes to prevent the use of performance-enhancing drugs like erythropoietin (EPO). The table below shows the results of blood tests conducted by an agency in 2015 and 2020.
| Year | Number of blood samples tested | Percentage of samples testing positive for EPO (%) |
|---|---|---|
| 2015 | 18,500 | 2.4 |
| 2020 | 42,000 | 0.8 |
Calculate the decrease in the number of blood samples testing positive for EPO between 2015 and 2020.
