What is the scientific effectiveness of "street preaching" as a method of evangelization?

Scientifically speaking, street-preaching, like all other preaching and teaching and all other means of evangelism, is zero percent effective. Conversion is a miracle and requires much more than street-preaching or any other kind of human effort. Asking such a question is like asking how effective it is to pour water into a container if you want to turn it into wine.

The street preacher prays for God's blessing, has Scriptural precedent since at least the time of Jonah, and the command to go into all the world and preach the gospel to every creature. He leaves the outcome with God.

The wind blows where it wills and no one can tell where it is coming from or where it is going... so it is with those born of the Spirit.

Scientifically speaking, the question's concepts are too open for interpretation for there to be any deducible, clear metrics:

• what exactly is being preached? For example, if the speaker adheres to young earth creationism (a concept not supported by some of the largest denominations), the preaching will statistically have a very different reception than, let's say, the golden rule.
• when and where is it taking place? If the speaker is on a metropolis avenue on a Monday morning at 8:45 AM, reception is statistically going to be very different than on a Sunday afternoon in the country side. In Europe, people are more likely to engage in discussion and counter arguments in long-standing traditions, like Speaker's Corner.
• how knowledgeable is the speaker on the topics he/she tries to convey?
• how knowledgeable is the average person passing in terms of demographics and time frame?
• how interactive is the activity? Is it mainly unidirectional, a dialogue, argumentative, etc.?
• are the location & time frame static (i.e. every Sunday afternoon in the same street, or one-time door-to-door)?
• is the subject matter specific or generic (per interaction)?
• are detailed records being kept of all interactions?
• what are the criteria for rating the interaction and its results?
• is there any follow-up?

All these variables will result in very different interactions and metrics according to sociology.

Arguably, the only more or less reliable metrics would come from:

• a neutrally moderated discussion between experts,
• with equal time on a specific matter,
• with a recorded audience vote before and after the interaction to measure the extent opinions have shifted or stayed the same in the audience.

A well executed example would be the Intelligence Squared series.

That is a question I have wondered about as well.

Here is what I could find with a simple google search . . .

http://www.christianitytoday.com/le/2010/summer/outsidersfindfaith.html?paging=off

Looking at the axiom that 85% of people come to Christ before their 18th birthday he says

People from an unchurched upbringing are a clear minority among evangelicals. (28% of people in church on a Sunday)

when someone from an unchurched background makes a lasting decision for Christ, it happens much later than we have often assumed and is spread out across every stage of life.

I must admit that the "85/18 Rule" was partially confirmed in my research. In fact 84.5 percent of evangelicals do accept Christ before that age. However, the statistic only holds true if they were raised in a home where both parents were Christians with either a high or moderate level of spiritual activity.

Taken together, these things suggest that faithful parents often bring their kids to the point of a decision (for or against) before they leave the parental home.

These kids of faithful parents will likely not be effective targets of "street preaching", as their parents have way more opportunities to train and reach them first. Street preaching may be effective for those from faith backgrounds who rebel against the family faith. (after they find life unsatisfying without faith)

I have been involved with mission and ministry on the rough edge (drug rehab, prison, food bank, soup kitchen) and in these places many people are dissatisfied with the way their life is now, and they may be more likely to listen to street preaching.

We have a guy who street preaches outside our Saturday Morning Farmers Market. People do not often stop and listen. I think he might be more effective if he had a relationship with his audience outside of just preaching at/to them. I can't speak to his calling as I don't know him. If God called him to this, then it is exactly where he should be, and what he should be doing.

I think street preaching works best with people already unsatisfied with their life.

This article quotes statistics from Thom Rainer, The Unchurched Next Door

http://backtochurch.com/participate/resources/statistics/

A majority (66 percent) of Americans are unwilling to receive information through an e-mail message, and 70 percent say e-mail would be ineffective in getting them to visit.

I put street preaching in a similar category. You feel like a target, not a person or friend. Because you are already on your way somewhere else, street preaching does not target people who don't feel they have time to stop.

What is the scientific effectiveness of “street preaching” as a method of evangelization?

Scientifically methodology seems to almost be non-exist in this subject matter. However history show that it is effective in making conversations. The lives of several historical persons bears this out.

We can see how St. Paul changed his preaching approach after his preaching in Athens about the Unknown God.

Historically speaking street peaching has been proven to be an excellent method of evangelization. Some believe that it dates back to biblical times. Had not Jonah in the streets of Nineveh had not preached to the inhabitants of Nineveh, would they have repented of their sins!

Open-air preaching, street preaching, or public preaching is the act of evangelizing a religious faith in public places. It is an ancient method of proselytizing a religious or social message and has been used by many cultures and religious traditions, but today it is usually associated with Evangelical Protestant Christianity.

Early Methodist preachers John Wesley and George Whitefield preached in the open air, which allowed them to attract crowds larger than most buildings could accommodate.

Motives for open-air preaching include to glorify God and to fulfill the command to preach and make God's Word known.

Some who believe street preaching is Biblical include examples such as Jesus in the Sermon on the Mount that of the prophet Jonah, who reluctantly obeys the command of God to go to the city of Nineveh and preach "Yet forty days, and Nineveh shall be overthrown!". Others listed include Paul's speech to the Athenians in Acts 17. However, others believe from scripture that Jesus was not technically a street preacher nor could possibly be one, "He shall not strive, nor cry; neither shall any man hear his voice in the streets."

The Christian Apologetics and Research Ministry lists the "many examples of street preaching in the Bible" as including Noah, Solomon, Ezra, Jeremiah, Jonah, John the Baptist, Jesus Christ, Peter, Paul, Phillip and Apollos.

St. Dominic and the first generations of Dominicans were seen all over Europe preaching the streets of various European cities.

St. Dominic's Plan Unique

In its plan and purpose the Institute is unique, for of all the orders of the Middle Ages the Friars Preachers was the only one formally approved by the Holy See for the single purpose of universal preaching. It had occurred to no other founder of a religious institute to petition the Holy See for permission to establish an order in which the practice of apostolic preaching, after long years of scientific training, should not be a temporary privilege but an inherent right.

It is true that, a century before, St. Norbert had received for himself a general permission to preach wherever he would. Afterwards it was suggested to him by the Bishop of Laon that he found an order for the purpose of continuing his work after his death. This he did, but provided for the administration of parishes as well as preaching in his institute. And although the followers of St. Norbert rapidly increased in number until they became a most numerous body, the division of their efforts between parish work and the larger apostolate of preaching rendered it impossible for them adequately to supply the urgent needs of the pulpit. This is clearly shown by the burning words of the Fathers of the Fourth Lateran Council deploring the lack of effective preaching in the Church. Nor does St. Norbert seem to have adopted any special measure to qualify them as a body to preach more effectiiely than the parish clergy. To St. Dominic, therefore, must be accorded the credit of having first conceived the splendid idea of an institute wholly given over to the extirpation of heresy and the propagation of the Gospel to the ends of the earth. The administration of parishes did not enter into its interests because St. Dominic desired his disciples to possess not a local but a universal character -- to preach the Word of God not one day in the week but every day. The chapter of 1228 decided the matter formally when it forbade the brethren to accept churches that carried with them parish obligations.

St. Francis of Assisi often preach in villages and in the outdoors!

I've heard the quote once too often. It's time to set the record straight—about the quote, and about the gospel.

Francis of Assisi is said to have said, "Preach the gospel at all times; when necessary, use words."

In his day, Francis was known as much for his preaching as for his lifestyle.

He began preaching early in his ministry, first in the Assisi church of Saint George, in which he had gone to school as a child, and later in the cathedral of Saint Rufinus. He usually preached on Sundays, spending Saturday evenings devoted to prayer and meditation reflecting on what he would say to the people the next day.

He soon took up itinerant ministry, sometimes preaching in up to five villages a day, often outdoors. In the country, Francis often spoke from a bale of straw or a granary doorway. In town, he would climb on a box or up steps in a public building. He preached to serfs and their families as well as to the landholders, to merchants, women, clerks, and priests—any who gathered ... - Speak the Gospel

In addition to Ken Graham’s excellent answer to this question, let me expand on the itinerant Protestant preachers who boldly declared the word of God in the open air, in fields and in public places, even when to do so would result in persecution. From 1660 and the restoration of the English Monarchy, non-conformists were forbidden to preach anywhere unless they were ordained by an Anglican bishop. John Bunyan, who wrote The Pilgrim’s Progress, was twice imprisoned for his failure to comply. https://en.wikipedia.org/wiki/John_Bunyan#Imprisonment

Other Protestant preachers who engaged in open air preaching include:

John Wesley, founder of Methodism declared, "I am well assured that I did far more good to my Lincolnshire parishioners by preaching three days on my father's tomb than I did by preaching three years in his pulpit ... To this day field preaching is a cross to me, but I know my commission and see no other way of preaching the gospel to every creature."

Wesley's contemporary, Anglican preacher George Whitefield stated: "I believe I never was more acceptable to my Master than when I was standing to teach those hearers in the open fields ... I now preach to ten times more people than I should, if had been confined to the churches."

It was said that one of the regular practices of America evangelist Dwight L. Moody in the late 1860s "was to exhort the passers-by in the evenings from the steps of the court house. Often these impromptu gathering drew as many hecklers as supporters."

Charles Spurgeon, the famous open-air Baptist preacher of England, believed that open-air preaching was instrumental in getting people to hear the gospel who might otherwise never hear it and many open-air preachers today believe that it reaches many more people at once than other approaches to evangelism do.

Groups such as Jehovah's Witnesses and Mormons are famous in particular for spreading their beliefs by door to door evangelism at people's homes, often in pairs or small groups. Source: https://en.wikipedia.org/wiki/Approaches_to_evangelism

Back in the 1960’s Jehovah’s Witnesses expected their ‘Special Pioneers’ to spend 150 hours every month (1,800 hours a year) going from door to door, and ‘Regular Pioneers’ did 100 hours every month (1,200 hours a year). A Jehovah’s Witness relative remembers engaging in street preaching back in the 1950’s, using placards and engaging in conversation with people in the High Street.

These days outdoor preaching, such as addressing crowds of people in parks or in other public places, seems to have ground to a halt because of the Covid pandemic. However, the U.K. Baptist church I attend held “drive-in” services in the town centre public car park. Anybody could turn up, sit in their vehicles with the windows down and hear the sermon and sing along to the hymns courtesy of a P.A. system. Several visitors to the town and people who did not belong to our church stayed to listen. There is no way to know whether anybody was converted to Christianity as a direct result, but historically many people have turned to Christ in faith after hearing the Gospel preached in some open-air or public venue.

What is the scientific effectiveness of street preaching as a method of evangelism? Pew Research is my "go-to" source of information for statistics on Christianity, but I drew a blank on this one. Back in the days of Bunyan, Wesley and Spurgeon, I doubt anybody stood with a note-book and pen to take names and addresses of people listening to an open-air preacher and then followed up six months later to enquire if said person was now a Christian. Fast-forward to the 21st century and our age of digital data overload, legislation now exists to prevent proselytisers from recording personal details of people they contact. Data protection legislation prohibits keeping such information on personal computers.

Some denominations keep detailed statistics on how much time they spend on speaking to members of the public outdoors, or speaking to them on their doorsteps, or how many pieces of literature they hand out. They also keep statistics on how many people are baptised by them each year - although I have never seen any breakdown on how many baptisms were genuinely new converts as opposed to how many were brought up in that faith and were then baptised later in life.

I suppose an organisation such as Pew Research could poll Christians to ask if their conversion was a direct response to hearing a street preacher. Whether that would be "scientific" or not I couldn't say.