Public sector transparency could be undermined and the public misled by the failure of some West Australian Government agencies to properly disclose financial information, the auditor general has found.

Colin Murphy assessed the 2014-15 annual reports of 50 agencies and found problems with 18.

They had either failed to include the audited version of their financial statements and key performance indicators (KPIs) or did not include the coming year's financial estimates, as approved by their minister.

"Failure to include reliable information in an annual report undermines transparency and could mislead readers about an agency's performance," Mr Murphy's report said.

The stated financial statements or KPIs of nine agencies were different from those audited by Mr Murphy.

The Commissioner for Equal Opportunity incorrectly reported the purchase of "non-current assets" as receipts from services, according to the report.

Several senior officers at the Department of Corrective Services had their pay incorrectly reported, some with their pay overstated and others understated.

The Department of Child Protection and Family Support "failed to disclose the ageing analysis of its financial assets", which indicates the extent of exposure to credit risk.

Staff errors to blame

The agencies explained these errors occurred because staff incorrectly changed figures after they were audited, mistakes were made during the preparation of the annual report, or prior versions of data were inadvertently included.

Eight agencies had not properly reported their ministerially-approved financial estimates in annual reports tabled in Parliament.

"This is a concern as the annual report is the only place the estimates of these agencies are published as they are not included in the state budget papers," Mr Murphy said.

The report did find, however, agencies "overwhelmingly satisfied" the requirement not to include comments or information in their annual reports that were inconsistent with their audited financial statements and KPIs.

Only two agencies were found to have committed "minor errors" in this area.

The auditor general reported agencies generally accepted the findings and confirmed they had already changed their annual reporting practices or would improve them.