Research suggests that are the most effective leaders.

I believe the answer is: democratic leaders
democratic leaders refers to the type of leaders that seek to understand the needs of the people that they led.
This often resulted in higher satisfaction from the people and would resulted in overall efficiency from the people that follow them.

Iconography, use of decoration, Christian subject matter, elaborate patterns, use of bright colors, the use of precious and valuable metals such as gems.

Explanation:

The characteristics of medieval art and culture are unique. Some characteristics of medieval art and culture such as iconography means the visual representation of images and symbols, use of decoration, Christian subject matter, elaborate patterns, use of bright colors, the use of precious and valuable metals such as gems. The use of luxurious items represents the higher social status in the society.