slow group by query

Is there any way to make this query faster? I have indexes on year,
msa_code, and sic. I've also tried it with
an index on the combined group by columns. I've made both sort_mem and
shared_buffers bigger, but still this query
takes 40 seconds when I select 4 msa_codes and 7 minutes when I select 40
msa_codes. Would it just be better
to transpose the table to begin with and avoid the group by all together?

SELECT b.msa_code, b.sic, b.own, b.ind_div,
(select emp from tbl_bls_msa as bls
where bls.year = '1975' and bls.msa_code = b.msa_code and bls.sic = b.sic
and bls.own = b.own and bls.ind_div = b.ind_div ) AS emp1975,
(select emp from tbl_bls_msa as bls
where bls.year = '1976' and bls.msa_code = b.msa_code and bls.sic = b.sic
and bls.own = b.own and bls.ind_div = b.ind_div ) AS emp1976,
(select emp from tbl_bls_msa as bls
where bls.year = '1977' and bls.msa_code = b.msa_code and bls.sic = b.sic
and bls.own = b.own and bls.ind_div = b.ind_div ) AS emp1977,
(select emp from tbl_bls_msa as bls
where bls.year = '1978' and bls.msa_code = b.msa_code and bls.sic = b.sic
and bls.own = b.own and bls.ind_div = b.ind_div ) AS emp1978,
(select emp from tbl_bls_msa as bls
where bls.year = '1990' and bls.msa_code = b.msa_code and bls.sic = b.sic
and bls.own = b.own and bls.ind_div = b.ind_div) AS emp1990
FROM tbl_bls_msa AS b
where msa_code in ('1680','1640','0040','0120','0080')
GROUP BY b.msa_code, b.sic, b.ind_div, b.own ;

NOTICE: QUERY PLAN:

Group (cost=635.97..695.18 rows=592 width=22)
-> Sort (cost=635.97..635.97 rows=5921 width=22)
-> Index Scan using msa_code_tbl_bls_msa_key,
msa_code_tbl_bls_msa_key,
msa_code_tbl_bls_msa_key, msa_code_tbl_bls_msa_key,
msa_code_tbl_bls_msa_key on
tbl_bls_msa b (cost=0.00..264.99 rows=5921 width=22)
SubPlan
-> Index Scan using msa_code_tbl_bls_msa_key on tbl_bls_msa
bls (cost=0.00
..53.71 rows=1 width=10)
-> Index Scan using msa_code_tbl_bls_msa_key on tbl_bls_msa
bls (cost=0.00
..53.71 rows=1 width=10)
-> Index Scan using msa_code_tbl_bls_msa_key on tbl_bls_msa
bls (cost=0.00
..53.71 rows=1 width=10)
-> Index Scan using msa_code_tbl_bls_msa_key on tbl_bls_msa
bls (cost=0.00
..53.71 rows=1 width=10)
-> Index Scan using msa_code_tbl_bls_msa_key on tbl_bls_msa
bls (cost=0.00
..53.71 rows=1 width=10)

Thanks.
Ellen
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