Chinyere, once the nutrient analysis is completed for both they can be standardized for comparison. If the 14-item questionnaire asks for estimates over the course of a week and the EPIC FFQ asks for estimate daily per year, both can be converted to average daily intake. Then any software package such as SPSS or SAS would be suitable to conduct comparisons. I am not sure of your research questions. Please specify so I might be of greater help.

Chinyere, your aims are unclear from the information you have provided. From what I can gather, you either want to see if the dietary intakes participants reported in the FFQ match up with what you have captured in the 14 item med diet short screener or you want to see if the dietary intakes (regardless of dietary assessment tool used) match to published Mediterranean diet descriptions. To do the first you would have to score the diet as reported using both tools according to a Mediterranean diet score (there are number published but try Trichopoulou et al. as a starting point). Once scored, you can compare how each dietary assessment tool categorised the population. This however is a little redundant and circular as whoever made the short screener should have done a step like this as validation of the screener. To do the second you would choose either the FFQ or screener and score the recorded dietary intake according to a published Mediterranean diet score. 

If you provide greater detail maybe I can be of more help.

Thanks Laura and Joan. Laura you are correct with your first guess. I am trying to see if the dietary intake reported by the participants in the FFQ is in compliance with what they have captured in the 14 item med diet short screener. Joan, that is my research question. From what you are saying Laura, i should carry out a correlation test on SPSS and also a Chi-square test? however, FETA produce data on both daily nutrient and food group intake when FFQs were analysed, so now which one of the data is appropriate to run test with. I am guessing the food group intake data.

For the statistics I think you should use measurement of agreement statistics for example bland-altman graphs or Kappa measurement of agreement for categorisation. As to whether you use the nutrient or the food group output if you are matching to a scoring system (which you should) then it will call for the food group output as most of the systems use intakes of  vegetables, fruits and nuts, legumes, unprocessed cereals, meat and meat products and  dairy products or some variation of this to characterise the Mediterranean diet.

Thanks again Laura.