index and seq scan

Hello List,

i have the following table with an index on appid:

dbl=# \d test
Table "test"
Attribute | Type | Modifier

-----------+--------------------------+-------------------------------------------------
id | integer | not null default
nextval('"test_id_seq"'::text)
time | timestamp with time zone |
appid | integer |
Indices: appid_idx,
test_id_key

dbl=# \d appid_idx
Index "appid_idx"
Attribute | Type
-----------+---------
appid | integer
btree

Ii want this index to be used in my query, but only the seq. scan is
used and i don't know why.
When changing the WHERE expression to 'appid < 10', the index is used
(see EXPLAIN command below).
Could someone please explain this behavior to me and how i can use the
index in the first query?

dbl=# explain select * from test where appid > 10;
NOTICE: QUERY PLAN:
Seq Scan on test (cost=0.00..1530.84 rows=81050 width=16)
EXPLAIN

db=# explain select * from test where appid > 10;
NOTICE: QUERY PLAN:
Index Scan using appid_idx on test (cost=0.00..70.20 rows=57 width=16)
EXPLAIN

regards
Tina