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In 2013 38% of those who are currently "single and looking" for a partner--have used online dating sites or mobile dating apps. Pew Research

In a 2019 Stanford paper "Disintermediating your friends", they found that " Meeting online has become the most popular way couples meet, eclipsing meeting through friends for the first time around 2013."

How couples met.
Rosenfeld, Michael J., Reuben J. Thomas, and Maja Falcon. 2018. "How Couples Meet and Stay Together.

          1995  2017
Online            2%   39%
Friends          33%   20%
Family           15%    7%
At Work          19%   11%
Bar/Restaurant   19%   27%
Primary or
Secondary school 10%    5%
Church            7%    4%
College           9%    4%
Neighbors         8%    3%

- Top 15 Most Popular Dating Websites
Top 10 Best Online Dating Sites | Top10BestDatingSites.com
Specialty sites:
Spark Networks - Hosts Niche Dating sites
  ChristianMingle.com (Christian Dating for Christian Singles)
  JDate.com (Jewish Singles)
      Others (Black, Catholic, Deaf, ...) at SparkNetworks
Others:
  OurTime.com (50+ singles),

See:
Online Dating Sites: Top 2015 Rankings
Which Online Dating Service is Right For Me?

GPS Dating:
GPS dating apps finds people who are currently physically in your vicinity.
Tinder, Grindr, OkCupid
Tinder: A Hook-Up App Women Actually Use | The Atlantic
Tinder has some usability issues. Bumble is similar but better.
See bumble vs tinder - Google Search

Statistics: M=Million

Online Dating Statistics	Data
Total number of single people in the U.S.	54 M
Total number of people in the U.S. who have tried online dating	40 M
Total eHarmony members	20 M
Total Match.com members *	15 M
Number of questions to fill out on eHarmony survey	400
Percent of male online dating users	52.4 %
Percent of female online dating users	47.6 %
Percent who say common interests are the most important factor	64 %
Percent who say physical charactersitics are the most important factor	49 %
Percent of marriages in the last year in which the couple met on a dating site	17 %
Percent of current committed relationships that began online	20 %
Percent of match.com members with children	44 %
Average number of dates to first kiss.	2

* A 2007 Scientific American article, "The Truth about Online Dating" says,
"A large company such as Match might advertise that it has 15 million members, however less than a million are actually paying customers who can respond to emails."

Some facts from 76 Interesting Facts about Dating and Relationships

• Couples usually wait until six to eight dates before they are willing to enter into an exclusive relationship.
• The most common time for breakups is around three to five months.
• On average, it takes between 12 to 14 dates before couples will trade house keys.
• Thirty-three percent of online daters form a relationship, 33% do not, and 33% give up.
• On free dating sites, at least 10% of new accounts are from scammers.
• Thirty-three percent of online daters form a relationship, 33% do not, and 33% give up.
• According to the U.S. census, there are 95.9 million unmarried people in the U.S. of which 47% are men and 53% are women.
• Researchers at the University of Chicago found that people were twice as likely to find a date through friends and family than through the bar scene.
• Over 50% of all singles in America have not had a date in more than two years.
• Nearly 40% of men do not feel confident meeting a woman for the first time.
• If a group of women are standing together but their eyes are wandering, they are likely to be looking for guys. If they each take a turn to break away from the group to head to the bathroom alone, they are on the prowl. If they are huddled together giggling, they are usually not interested in finding men.
• Beautiful women typically get more stares, winks, and harassment than average-looking women do, but they are also less likely to get asked out by average-looking men because those men tend to be intimated by them.
• The appropriate time to call after meeting a man or woman is hotly debated among dating experts. Typically, the ideal time to wait to call is two to four days, though no longer than four to five days. Calling too soon can appear desperate.
• Dating specialists suggest that if a woman doesn't return a call after two messages, she is not interested.
• An attractive online "About Me" section in your online dating profile often includes a brief description of what you are passionate about or thankful for, a couple of things your friends say about you, qualities you are looking for in a potential partner, the first thing people notice about you (other than appearance), how you spend your leisure time, five things you can't live without, and the latest good book you've read.
• Humans like mystery and "the chase," so don't be too "available" to a date. Dating experts typically suggest not sleeping too early with a date because the longer the chase, the more likely love will blossom.

Matching algorithms are getting more sophisticated.
Match.com bases its matchmaking on the Myers-Briggs personality test. eHarmony pair people up using their "secret key dimensions of compatibility" which are grouped into core traits and vital attributes.

A 2012 Health.com article reported at CNN says,
"Some services, such as eHarmony and PerfectMatch.com, claim to minimize the guesswork involved in online dating by using mathematical algorithms to match couples according to various traits -- including, in one case, the ratio of index- to ring-finger length (said to be a marker of testosterone levels).

The authors of the review are skeptical of these claims. They weren't able to find a single rigorous study showing the effectiveness of the algorithms, and other research suggests it's extremely difficult to predict the likelihood that a relationship will succeed before two people meet."

They go on, "One of my greatest concerns about online dating has to do with what I call "the click problem." We already have a commitment problem in America, one of several reasons why roughly half of first marriages and about two thirds of second marriages here end in divorce. Online dating probably is making things worse."

"These many problems notwithstanding, the future of online dating and matchmaking looks bright."
"Phase two companies like eHarmony and PerfectMatch have more sophisticated match algorithms."

In an Experiment with 5 men and 5 women at Chateau Heartiste, the hotest woman got 236 messages the 2nd got 128 and the other 3 got less than 20. The hotest man only got 14.

First Dates and Attractiveness Attributes:

• Relationship experts say that on a first date, it's not necessarily the content of a conversation that matters but the chemistry generated by the couple.
  You might learn more about a potential romantic partner by observing and letting conversation flow than by asking pre-set questions.
  Being a good listener tells you more about a first date than being a good talker.
• In a survey of 5,000 singles conducted by Match.com, 43% said fresh breath mattered the most before a date, 17% said stylish clothes, 15% said sexy fragrance, 14% said good skin, and 10% said great hair.
• Studies show that before a man even speaks a word, the way he stands (whether he is slouching or not) counts for over 80% of woman's first impression.
• Studies show that happiness is contagious and that potential dates find it hard to walk away from happy people. One of the biggest turn-offs during a date is negativity.
• Mirroring, or repeating someone's body language, often impresses a date because it subtly conveys interest to the other person. One should avoid copying every move, however.
• Body language studies show that revealing areas of the body that aren't usually on display (such as the inner wrist, the inside of the upper arm, ankles, feet, inside calf muscle, and the nape of the neck) has an immediate effect on a date and shows an instant liking.
• If you want to create an instant link with a date, say his or her name at least twice in the conversation. This shows attentiveness and connectiveness.
• Studies show that remembering bits of information about a person and working them into conversations not only is highly flattering but also shows interest.
• Bad breath and bad teeth are an instant turn-off for potential dates. If deep dental cleaning doesn't improve a person's breath, he or she could have a stomach bacterium called H. pylori, which causes bad breath.
• Research has confirmed that women are more attracted to men who wear pheromone-based colognes or aftershaves such as 10X. Studies have also shown that women, who have a stronger sense of smell than men, are particularly attracted to musk and black licorice smells.
• Top ten turn-offs for women include cystic acne, raggedy nails, flatulence and belching, missing teeth, body odor, bad breath, hairy nostrils, "man boobs," "goofy" glasses, and hair "mistakes.
• When a man first approaches a woman, she will base 55% of her initial impression of him on his appearance and body language, 38% on his style of speaking, and 7% on what he actually says.
• If a woman is interested in her date, she will often smile at his jokes, play with her hair, fidget with an object such as a glass, blush when he pays her a compliment, pout or pucker her mouth, stumble over words, or lean in towards him.
• The appropriate time to call after meeting a man or woman is hotly debated among dating experts. Typically, the ideal time to wait to call is two to four days, though no longer than four to five days. Calling too soon can appear desperate.
• Choosing exciting places for a first date increases the chances of the other person falling for you. There is a definitive link between danger and physical/romantic attraction.
• Five types of women that men tend to avoid are serial flirters, someone who talks about marriage too soon, clingy women, the party-girl, and a woman who talks too much or is drama queen.
• Four common date blunders include showing up late, talking about yourself too much, revealing too much about your ex, and an obvious over-eagerness.
• A man's top dating fears include that a woman will come between him and his friends, won't allow him free time, will turn out to be a stalker, won't respect him, or will be too high maintenance.

What's more important on a first date? at Online Dating Statistics | StatisticBrian

Personality	30 %
Smile & Looks	23 %
Sense of Humor	14 %
Career & Education	10 %

Sex:
The topic that comes up frequently is how long to wait before you have sex.
The answers range from 3 dates to 3 months.

Or, of course, the conservative religious view is not till you're married.
The best answers are something like "It is not the number of dates, but much more the connection and chemistry between the two of you....... "
See 7 signs you're ready to have sex with your date | Happen Magazine at match.com.

While the women who were surveyed went to great lengths to screen online acquaintances before meeting them, nearly a third reported having sex on the first date and three-quarters of those said they did not use condoms, according to the study by The University of Texas School of Public Health. Source Houston Chronicle

In 12 Rude Revelations About Sex | Psychology Today they say,
"Whatever discomfort we feel around sex is commonly aggravated by the idea that we belong to a liberated age--and ought by now to be finding sex a straightforward and untroubling matter, a little like tennis, something that everyone should have as often as possible to relieve the stresses of modern life."

Safety - Warnings - :
There are some basic guidelines at geek-2-geek In March, 2012 Match.com, eHarmony and Sparks Networks (operator of JDate and ChristianMingle) announced they will scan the histories of possible clients for sexual assault, identity theft and violence before allowing them access to their fee-based sites. Source: TIME.com
However, a clean background check only means the person hasn't got caught.

• Use Caution | geek-2-geek
• FBI - Beware of Online Dating Scams
• Background Check Services Offered | RomanceRealityCheck.com $69 for criminal check, $99 for criminal and sex offender search

Links:
Top 15 Most Popular Dating Websites
Online Dating Website Reviews | Reviewing The Best & Worst Sites
The Top 10 Online Dating Sites of 2013
Find Love Using Internet Dating, Find Out How
76 Interesting Facts about Dating & Relationships
Which Online Dating Service is Right For Me?
The Truth about Online Dating: Scientific American, Jan 2007
Psychologists highlight pitfalls of online dating - CNN.com
Online Dating Statistics | Statistic Brain
Results From An Online Dating Experiment | Chateau Heartiste
Is Online Dating Site's Matching Criteria Sexist?
When to Send a Woman Flowers / When NOT to Send a Woman Flowers MidLifeBachelor.com
Choosing a Good Online Dating Username is Like Writing a Hit Song
Pick An Online Dating Username That's Unique, Find Love Using Internet Dating