JUDY WOODRUFF: It was another tough day for the financial markets, capping a volatile week, one marked by anxiety over interest rates, the dollar, and falling oil prices, among other things.

More puzzling in some ways, there was good economic news earlier this week, and that still seemed to upset investors. What's happening here? And does the volatility of recent weeks suggest the end of a bull market?

Well, Mark Vitner is a managing director and senior economist at Wells Fargo, and he joins me now.

So, Mark Vitner, how do you explain all this volatility and especially the downward move after this good news on jobs last week?

MARK VITNER, Wells Fargo: Well, I think it's really just part of the adjustment process.

We have had interest rates stuck at zero for eight years now, and the economy has improved to the point where the Federal Reserve is likely to raise interest rates probably in June, but probably no later than September. They're almost definitely going up this year.

And that causes people to reassess how they position certain investments. Companies that are interest-rate sensitive are now falling out of favor. And we have got a lot else going on in the world that's unnerving the markets. The dollar has strengthened tremendously and has done it very fast. And we have had this incredible slide in oil prices, which you would think is a good thing, but it's got some people questioning why on earth are prices falling so far so fast.

JUDY WOODRUFF: Well, first, on interest rates, hasn't the Fed been giving a warning for months now that some hike in interest rates is coming? Why aren't there baked-in expectations about that now?

MARK VITNER: Well, you would think that people would be used to this idea. But the Fed's been thinking about raising interest rates for a long time, and it's the first time that we have ever had to start from zero. The federal funds rate is roughly around 10 basis points, and we have never had to move away from the zero interest bound before.

And folks are really wondering, how vulnerable is the economy, how well can we take a quarter-point or a half-point increase in interest rates over the next few months? My gut tells me that I think the economy is plenty strong, we will be able to withstand it. But the Fed will move cautiously, and it's still — it's the adjustment. It's the shift from having rates at zero for eight years to going in an interest rate — a rising interest rate environment that's unnerving the market.

JUDY WOODRUFF: Well, what about one of other things that you mentioned, and that is the strengthening dollar, strengthening against other currencies, especially the euro? What about that? What's behind that and how serious a concern is it?

MARK VITNER: Well, in terms of what's driving the dollar up, we're in a much different place than Europe is right now.

In many respects, the United States is the strongest economy in the developed world right now. We're — the Federal Reserve stopped purchasing bonds in our market well over a year ago, back in late 2013. The European Central Bank just embarked on their own quantitative easing, where they're purchasing securities.

And here, we're getting ready — we're getting set to raise interest rates, so capital is flowing into the United States. And that's likely to continue. But, again, is a stronger dollar, is it good news or bad news for the U.S.? It's good news. We have a trade deficit. We import more than we export.

And the stronger dollar certainly is going to hurt parts of the economy. Some manufacturers will be disadvantaged. But for the economy overall, it increases our purchasing power. It will be a good thing. It's just the adjustment process in going from a — in going towards a stronger dollar that's so difficult to — for the financial markets to take.

JUDY WOODRUFF: But, just very quickly, Americans, you're saying, should sleep soundly tonight, rather than lying awake, worrying about a lot of this?

MARK VITNER: Well, a lot of times, when the market goes down, people are like, woe is me, what's going on here?

You have to remember that, while we have had some big declines this past week, we're very close to all-time highs in the market. In valuations, I wouldn't say the stock market is overvalued, but it's fully valued. And so now that we're going into a different economic environment, one that's going to have a stronger dollar, one where interest rates are likely to rise a little — they're still likely to remain relatively low — folks are going to have to adjust their portfolios somewhat.

JUDY WOODRUFF: Mark Vitner with Wells Fargo, we thank you.

MARK VITNER: Good to be with you.