Which of the Following Studies Would NOT Have a Possible

Multiple Choice

Which of the following studies would NOT have a possible threat of observer bias?

A) A study looking at the effect of eating fruits and vegetables and general physical fitness
B) A study looking at the effect of tutoring on SAT scores
C) A study looking at whether increasing the number of hours listening to music increases singing ability
D) A study looking at the effect of increasing the rate of text messaging in a day on writing/English composition skill