Americans are often thought of as people who believe in God.

But results of a new Harris Poll show that may be changing.

The poll found that 42 percent of all U.S. adults said they are not "absolutely certain" there is a God, including 15 percent who are "somewhat certain," 11 percent who think there is probably no God and 16 percent who are not sure.

Not everyone who described themselves as Christian or Jewish said that they believed in God. Only 76 percent of Protestants, 64 percent of Catholics, and 30 percent of Jews said they are "absolutely certain" there is a God. However, most Christians who described themselves as "born-again" (93 percent) said they are absolutely certain there is a God.

Differences Between Demographic Groups

Demographic groups that are more likely to say they are absolutely certain that there is a God include:

People in all age groups 40 and over compared to people in age groups under 40
Women (62 percent) slightly more than men (54 percent)
Blacks (71 percent) compared to Hispanics (61 percent) and whites (57 percent)
Republicans (73 percent) more than Democrats (54 percent) or Independents (51 percent)
People with no college education (62 percent) or who have some college education (57 percent) compared to college graduates (50 percent) and those with post-graduate degrees (53 percent)

About 35 percent of all adults polled said that they attend religious services at least once a month, including 26 percent who said they attend every week or more often than that.

Nearly half of all adults polled (46 percent) said they attend services a few times a year or less frequently, while 18 percent said the never attend religious services.

Those who said they attend religious services once a month or more included 48 percent of Protestants, 46 percent of Catholics, and 12 percent of Jews. However, more than two-thirds (68 percent) of born-again Christians attend Church once a month or more.

Is God Male Or Female?

The public is almost equally divided between those who think of God as male (36 percent) and "neither male nor female" (37 percent), with 10 percent saying "both male and female." Only 1 percent thinks of God as a female.

Does God Have A Human Form?

Much of the public (41 percent) thinks of God as "a spirit or power that can take on human form but is not inherently human," according to the survey. But 27 percent think of God as a "spirit or power that does not take on human form," while 9 percent of adults think of God as being "like a human being with a face, body, arms, legs, eyes, etc."

Does God Control Events On Earth?

Only 29 percent of those polled said they believe God "controls what happens on Earth." Of those believers, 57 percent were born-again Christians. And 44 percent of respondents said they believe that God "observes but does not control what happens on Earth."

Do We Worship The Same God?

Poll results show that about 51 percent of all adults, including a majority of Catholics (63 percent), believe that Jews, Christians and Muslims all worship the same God. One-third (32 percent) said they believe they do not and 16 percent are not sure. On this question, as on the others, the views of born-again Christians are different -- a 54 percent majority believes they do not worship the same God and only 34 percent believe they do.

Are Believers Declining?

Three years ago, in an identical survey, 79 percent of adults said they believed in God and 66 percent said they were absolutely certain that there is a God. In this new survey, those numbers declined to 73 percent and 58 percent respectively.

Why The Changes?

There are some important differences between telephone polling and those conducted online, as this survey was. Several surveys find that people are more likely to admit potentially embarrassing beliefs of behaviors when answering online surveys than to admit these behaviors when talking to an actual interviewer on the phone.

According to Harris, people are three times more likely to say that their sexual orientation is gay, lesbian or bi-sexual online than over the phone. Researchers called this unwillingness to give honest answers to some questions in telephone surveys a social desirability bias.

This distinction between online and telephone polls may explain why more people said they are not absolutely certain there is a God than have given similar replies in other surveys conducted by telephone.

The Harris Poll was conducted online by Harris Interactive between Oct. 4 and 10 with a nationwide sample of 2,010 U.S. adults.