I need to trend by DOB and Diagnosis (how many people with same DOB and same diagnosids). Im not sure what the best way to do this is? I tried the vlookup but that didn't work. Here's an example of my column headings. My spreadsheet goes to line 371.

Date Census Day Hospital Inpatient Referrals DOB DX
8/22/12 14 None 2/2/1892 Cancer

You don't use VLOOKUP for anything other than looking up a piece of information in a reference table and bringing back a different piece of data from the matched row. That's what VLOOKUP is for. It's not a statistical function.

You could read up in Excel's help files on TREND if that is truly what you want. It may not be.

Perhaps you should look at COUNTIFS() function, or try a PivotTable.