Some data is lost when I join an Excel file to a shapefile

[Institute_forPublic_Strategies]

I have a census tract shapefile and an Excel file in which one of the fields is census tract number (field = Site_Tract). I am trying to join the Excel file to the shapefile using the common census tract number field. I have verified that the two common fields have the same number type (double), number of decimal places, and significant digits. But when I do the join, some of the records are populated with 'null.' What am I doing wrong?

[Institute_forPublic_Strategies]

Through a work-around, I finally got the join to work but not without complications. Just for the record, I encountered these problems when I played around with data types: 

1) I created a new 'text' field in both tables but that still produced the null values when I did the join.

2) I then created a new numeric field, short integer, decimal places = 6 in both tables; again.....some null values, but not as many as before. One thing that I thought was odd was that I assigned it 'short integer' in the fields view but after I saved it, it converted the field to 'long integer.' Even though I pretty much repeated this same step over and over, I don't know why

• 'short' integer worked over 'long,'
• it won't join tables in which the common fields were both 'double' numeric types
• short integer was changed to long integer after I saved the addition of the new field in fields view.

Thanks for all your help!