A published study follows a large group of women with treated and untreated (treatment was not assigned by researchers) dysplasia of the uterine cervix, documenting the number who improve, stay unchanged, or progress into cervical cancer. They found that the risk of cervical cancer was higher in the untreated group. This study design is best described as which one of the following:

Select one:

a. Case-control study

b. Cohort study

c. Descriptive study

d. Experimental study