I designed a survey (mostly Likert scales) and began to collect responses. After collecting several responses I decided to include an additional scale comprised of 9 items. The newly added scale will be an important predictor. My dependent variables are themselves Likert scales. I will do ordinal probit regression.
Collection before adding the new item was ~200, but total sample size is expected to be ~500.
Should my data be considered to be MCAR, MAR, or MNAR? What is the best way to handle such missing data?