Medical researchers have developed a new cream for treating skin rashes. To test their cream they set up an experiment where one group of patients used the new cream for two weeks, and a second group used no cream.


In each group, the number of people whose skin condition got better and the number whose condition got worse are recorded below. Because patients do not always complete studies, the total number of patients in each of the two groups is not exactly the same.


Of 298 patients who used the cream, 223 found their rash got better and 75 found their rash got worse.

Of 128 patients who used no cream, 107 found their rash got better and 21 found their rash got worse.

What numbers should you compare to determine whether the cream is effective?
1) 298 v 128

2) 223 v 107

3) 75 v 21

4) 75/223 v 21/107

5) 223/330 v 75/330

6) 223/298 v 107/128

7) 223/298 v 75/298