The Westpac Banking Corp (ASX: WBC) share price is down 0.4% to $21.85 at the time of writing.
Over the past 12 months, the oldest bank in Australia has also delivered the worst share price performance of the ASX 200 big four banks.
The Westpac share price is down 16% over the period.
This compares to a 7% dip in the Commonwealth Bank of Australia (ASX: CBA) share price and an 8% decline in the National Australia Bank Ltd (ASX: NAB) share price.
The Australia and New Zealand Banking Group Ltd (ASX: ANZ) share price is down 12%.
What's been happening lately with ASX bank shares?
As my Foolish colleague Bernd reported, September was a crummy month for ASX bank shares.
The Commonwealth Bank share price slipped 7% during September. NAB shares closed the month down 5.8%. The Westpac share price lost 4.5%. ANZ shares dipped slightly by 0.1%.
It was a bad month for the market at large, with the S&P/ASX 200 Index (ASX: XJO) down 7.3%.
What's happening with the banks is that investors are worried about rising interest rates. While they might mean increased net interest margins (NIMs) for the banks, they could also cause mortgage lending to fall and bad debts to rise.
NIM is the difference between the interest the banks are raking in on loans, and the interest they are paying out on savings deposits. Obviously, a rising official cash rate impacts both sides of the coin.
While the banks have been quick to pass on the official rate rises to home loan customers, they've been slower to increase the interest paid on savings accounts.
We'll get the data on NIMs soon enough, with NAB, ANZ, and Westpac completing their FY22 financial year on 30 September.
ANZ will report its full-year results on 27 October. Westpac will report on 7 November and NAB will report on 9 November.
Why has the Westpac share price fallen the most?
As reported on Livewire, Goldman Sachs analysts Andrew Lyons and John Li issued a research note on Wednesday in which they say Westpac is a buy.
They point out that Westpac was the worst defender of profitability over the period from FY13 to now.
But they like Westpac shares over the other big four ASX 200 banks right now for four reasons.
Firstly, the company's performance is strongly leveraged to rising interest rates.
They also note superior cost management and Westpac's latest market update, which indicated the bank is continuing to invest in itself.
As my Fool friend James reported at the time, the update included the status of the Customer Outcomes & Risk Excellence (CORE) program, new climate commitments, the bank's digital capabilities, and plans.
Lyons and Li also cite Westpac's "supportive share price valuations".
The Westpac share price is the lowest of the big four ASX 200 bank shares.
According to the ASX website, Westpac shares are trading on a price-to-earnings (P/E) ratio of 15.05.
This compares to a P/E ratio of 16.74 for CBA, 14.39 for NAB, and 10.23 for ANZ.
