How do I do an outer join between all nested subqueries? (getting an error of 'OUTER' is not a valid input for this position)

I have this query:

SELECT AVG(a.score) AS Average1, AVG(b.score) AS Average2, AVG(c.score) AS Average3
FROM 
(SELECT subfactor.score, dateID, EmployeeID 
    FROM employeescore 
        LEFT JOIN subfactor 
        ON employeescore.SubFactorID = subfactor.SubFactorID 
            LEFT JOIN factor 
            ON subfactor.FactorID = factor.FactorID 
            WHERE DateID='Jan2015' AND employeescore.EmployeeID='1' AND subfactor.FactorID='A1')a 
OUTER JOIN 
(SELECT subfactor.score, DateID, EmployeeID 
    FROM employeescore 
        LEFT JOIN subfactor 
        ON employeescore.SubFactorID = subfactor.SubFactorID 
            LEFT JOIN factor 
            ON subfactor.FactorID = factor.FactorID 
                WHERE DateID='Feb2015' AND employeescore.EmployeeID='1' AND subfactor.FactorID='A1')b 
ON a.EmployeeID = b.EmployeeID
OUTER JOIN
(SELECT subfactor.score, DateID, EmployeeID 
    FROM employeescore 
        LEFT JOIN subfactor 
        ON employeescore.SubFactorID = subfactor.SubFactorID 
            LEFT JOIN factor 
            ON subfactor.FactorID = factor.FactorID 
                WHERE DateID='Mar2015' AND employeescore.EmployeeID='1' AND subfactor.FactorID='A1')c 
ON b.EmployeeID = c.EmployeeID; 

Basically I want to select the averages of the three scores and I want to display the output regardless if one of the joined sub queries doesn't have any records. But I keep getting an error of ('OUTER' is not a valid input for this position). How can I repair?