Sound and the fear factor

I want to see how and why it is the music which adds to the fear factor. I asked my sister, who fits in with my target audience to watch 'The Strangers' trailer with and without sound to see how effective she thought the sound is and why. I didn't want to do this myself as my results may have been biased. However, by my sister telling me how effective she thinks sound is in a trailer and why and what she liked about it, I can chose and incorporate a soundtrack which my target audience will think is effective.

What have I learnt and how will I use this research?
From this research, I want to include a fast paced soundtrack for the disruption in the narrative as this will keep the audience on the edge of their seats. I also want to consider repeating parts of a soundtrack as it suggests time isn't passing by and the characters are struggling for help. This will be effective in the build up to our montage and the montage itself as it will show fast paced action. Also for the sting at the end and the jump shots, like the one of the antagonist walking down the stairs, I want to include sound effects such as bangs to make the audience jump as this is something my sister said she liked and makes the audience jump.