Acknowledging that some searches were giving people stale results, Google revised its methods on Thursday to make the answers timelier. It is one of the biggest tweaks to Google’s search algorithm, affecting about 35 percent of all searches.

The new algorithm is a recognition that Google, whose dominance depends on providing the most useful results, is being increasingly challenged by services like Twitter and Facebook, which have trained people to expect constant updates with seconds-old news.

It is also a reflection of how people use the Web as a real-time news feed — that if, for example, you search for a baseball score, you probably want to find the score of a game being played at the moment, not last week, which is what Google often gave you.

“This is the result of them saying we need to find a way to more effectively get fresh content up,” said Danny Sullivan, editor of Search Engine Land and an industry expert. “It does help with the issue of people thinking, ‘Wow, if I need to find out about something breaking, I’ll go to Facebook or Twitter for that.’ ”

Timeliness has long mattered to Google and its search results. Nevertheless, the company said that it always looks for improvements, and the latest change goes much further in freshening search results. Google tried once before to create real-time search, in 2009, when it introduced google.com/realtime, a service that incorporated Twitter posts that Google paid Twitter to use. But that contract expired in July and the two companies could not agree on terms to renew it, so Google disabled the site.

Americans still turn to Google for two-thirds of their Web searches, but for people who want the latest chatter about events happening now, it competes with Facebook, Twitter and Bing, Microsoft’s search engine, which includes more Twitter and Facebook posts than Google does in search results.

“The biggest source of the very freshest information is Twitter, and Google doesn’t have anywhere near the access to that kind of data as it had before,” Mr. Sullivan said. “But when people do those kinds of searches, they’re looking for a lot of reactions, looking for Twitter itself. So even with these changes, this doesn’t really solve that problem.”

Google became dominant by finding archived Web sites and showing links to them. But today people sometimes expect years-old links, like the best banana bread recipe; week-old links, like the last episode of “Gossip Girl”; or seconds-old links, like this morning’s presidential campaign news.

Google makes more than 500 changes to its algorithm a year, but most affect only a small percentage of results. With its new formula, which Google calls a freshness algorithm, Google tried to teach itself the difference between those types of requests, Amit Singhal, a Google fellow who works on search, wrote in a blog post announcing the changes.

“Depending on the search terms, the algorithm needs to be able to figure out if a result from a week ago about a TV show is recent, or if a result from a week ago about breaking news is too old,” he wrote.

“This algorithmic improvement is designed to better understand how to differentiate between these kinds of searches and the level of freshness you need.”

Google last announced a significant change to its search algorithm in February, when it said it would raise the rankings of high-quality sites to fight low-quality ones, often described as content farms, that were flooding the search engine with mindless articles tied to popular search queries.

The new formula, which affects search results globally but will not change nearby ads, will bring up minutes-old results for recent events, like an unfolding news story, and for recurring events like the Oscars or a political campaign. It will also show fresher results for topics that are often updated, like reviews of a new iPhone. It will understand that unlike breaking news, reviews from a few weeks ago are also useful, the company said.

These are “queries we don’t think we’re doing perfectly well on,” said Rajan Patel, a Google software engineer who worked on the new algorithm. “We just realized that people expect Google to return the most up-to-date results for all kinds of queries, from hot topics to more general queries like a TV show.”

For evergreen results, like recipes or how to change a tire, Google said the algorithm would know to show the best results no matter when they were posted.

The algorithm uses technology that Google built last year in response to the greater speed at which people were publishing updates online. It is a Web indexing system it calls Caffeine, which crawls the Web more quickly, updating Google’s index of Web sites continuously instead of every couple of weeks. Thursday’s revision changes how Google ranks those links now that it has them in its index, Mr. Patel said.

Google’s main competitor, Bing, has also developed a way to index Web sites that change often, like blogs and news feeds, and analyzes Twitter posts to identify popular topics, said Stefan Weitz, senior director at Bing.

Mr. Patel said that Google planned to incorporate posts from Google+, its new social network, into its search results to further improve their freshness.

In the world of marketing, everyone’s favorite question is “What’s my ROI?” ROI (return on investment) is all about knowing what you’ll get out based on what you put in. If you spend X amount of dollars on a television commercial, how many people will see it? How does that affect your sales? In an economy where every dollar is being stretched to its maximum potential, companies are unwilling to part with their budget unless they know it is going to be worth it in the long run. Understanding the ROI of a search engine optimization (SEO) campaign is just as important as understanding the ROI of running a radio advertisement. So what exactly should you be looking at when determining the success or failure of your SEO efforts? Here are a few factors to take into consideration:

1. Traffic to your site

A great way to see how well your SEO is doing is to look at your site’s traffic. You should see a steady increase in traffic over time, especially once your SEO begins to build momentum. You don’t want to see peaks and valleys; this means that your SEO efforts aren’t consistent. Peaks and valleys could also be an indication of black hat SEO tactics being used to promote your site. Black hat SEO provides short bursts of success, but no long-term, sustainable gain. I used to include search engine rankings as the main goal, but since rankings fluctuate so much these days, it is becoming less of a key SEO measurement metric.

2. Online presence

Part of conducting a successful SEO campaign is link building. One component of link building is the creation of business profiles on sites like Yelp, Merchant Circle, Google Places and so forth. As these profiles age, they will start to rank in the search engines. Depending on how competitive your industry is, these profiles can rank well when a user searches for keywords that you have incorporated into your profiles. The better your profiles rank, the more you can dominate the search results and increase your online presence. If your SEO is doing a good job of increasing your online presence, you should see your site showing up in the search results more and more frequently, and from a variety of sources. Aside from business profiles this can include directory listings, blog posts, press releases, social networking sites and more.

3. Bounce rate

Your bounce rate is a good indication of how well you site has been optimized, a critical component of any SEO campaign. A lower bounce rate means that more targeted traffic is being delivered to your site. It also is a good indication that your site’s user-experience is matching up with your visitors’ expectations. If a visitor can find the information they are looking for and is drawn further into your site, your bounce rate will go down. Bounce rate shouldn’t be the end-all-be-all measurement of success, however. If the goal of your site is to get someone to pick up the phone and call, they might not hang around once they find your phone number. If that is the case, your bounce rate might be high, but that isn’t necessarily an indication of bad SEO.

4. Conversion rate

Your site’s conversion rate is arguably the best way to measure the success of your SEO. Every site’s conversion metric is different. Do you want someone to pick up the phone? Sign up for a newsletter? Download a white paper? Whatever your site’s goals are, your conversion metric is a reflection of that. An increase in your conversion metric is good sign that all of your SEO efforts are working together. More targeted traffic is being directed to your site, which means that you’ve gone after the right keywords and are ranking well for them. A higher conversion rate also means that your site is keeping visitors engaged once they get there.

These four ways to measure the success of your SEO campaign are by no means the only way to determine how well or poorly your SEO is doing. They are, however, a good place to start and prove ROI. Being able to show a growth in traffic and conversion rates, among other things, is tangible proof that what you are doing is working.

Written by Nick Stamoulis who is the President and Founder of Brick Marketing (http://www.brickmarketing.com), a Boston SEO services company. With over 12 years of industry experience, Nick Stamoulis shares his knowledge by posting daily SEO tips to his blog, the Search Engine Optimization Journal and publishing the Brick Marketing SEO Newsletter, read by over 130,000 opt-in email subscribers.

Use the Bing™ Webmaster tools to improve your site’s SEO, submit your sites and XML-based Sitemaps to Bing, get data on which pages of your site have been indexed, backlinks, inbound links and keyword performance.

It is common for search marketers to become so consumed with Google that they often forget about another reliable traffic source in Bing. While Bing and Yahoo combine for roughly 25 percent of search traffic, perhaps that index warrants closer attention.