respondent_1: 123, 456, 789, 159, 753, ...<br>
respondent_2: 753, 654, 987, 321, 963, ...<br>
..etc...

##</code><code>##

count respondents who gave response x and response y

##</code><code>##

select count(*) from theTable where (response_id_x=1 and response_id_y=1);

##</code><code>##

respondent_id, response_id

##</code><code>##

select count(*) from theTable A inner join theTable B on (A.respondent = B.respondent) where (A.response_id = x and B.response_id = y);

##</code><code>##

SELECT COUNT(*) FROM table_X JOIN table_y ON (table_x.respondent = table_y.respondent)