I have a dataset where I have 100 respondents. Each respondent has to give response on service quality of Health care equipment. Is it providing efficient services to the patients? We have two columns 'Expected service quality' and 'Perceived service quality'. We will perform this equation= Service quality=Expected-Perceived to see if the service quality is positive or negative. If the difference is negative, it states we need improvement in that area. Now the problem is the two columns have many missing values and I have to perform paired t test on the data. In the first column there are 15 missing values and in 2nd I have 56 missing values. How do I deal with these missing values?