For lists within lists, use a hierarchy of bullets and then dashes:
The main outcomes of the project were:
- development of a new method for assessing risk by
- age of the population at risk
- level of exercise
- improved reliability for predicting stroke based on these factors
- promotion of the new method through local and international agencies.
Do not use a colon at the end of the lead-in phrase to the secondary list, or a full stop at the end of the secondary list.