A Governor's Prayer for Rain: An Empirical Analysis of a Supernatural Claim

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ON TUESDAY, NOVEMBER 13, 2007, Sonny Perdue, the Governor of Georgia, led a group of approximately 250 persons, including many state officials, in a prayer for rain on the steps of the state capitol in Atlanta. (1) Georgia had been suffering an extreme drought, and the level of Lake Lanier, an important water reservoir near Atlanta, had been decreasing dramatically over several months. Governor Perdue believed that a divine intervention was necessary and so he boldly asked God to bring rain. Fully expecting his prayer to be effective, Perdue said "Hopefully we will be better conservators of the blessings God's given us as he gives us more [rain]." (1) At the time and place when the state's highest ranking officer pleaded to the Almighty, it was cloudy, but it did not rain. However, sure enough, the next day there was light rain in Atlanta and much rain came to the area over the next couple of months. Many Georgians considered Perdue a hero and thought that his prayer had influenced God to increase rain/all to the drought stricken vicinity of Atlanta. But did it? Although there may have been constitutional problems with the Governor's prayer, (2) the purpose of this investigation is to determine whether the prayer was correlated with an increase in rain, and if so, how likely it was to have caused the increase.


When asked by reporters what outcome he expected from his prayer, Governor Perdue replied "God can make it rain tomorrow, he can make it rain next week or next month." (1) Although this is rather vague, I decided to give Perdue some leeway and use his own words to help define a time period to be assessed. The Governor presented his prayer on November 13, 2007, so "next month" was December 2007. It seemed reasonable to examine the amount of rainfall during the 48 days after the day of prayer, from November 14 through December 31, 2007, which I shall call the "post-prayer period." For comparison, a "pre-prayer period" was defined as the 48 days from September 26 through November 12, 2007. The day of prayer itself was not included in either of these pre- and post-periods since part of that day fell before the prayer and part of it fell after the prayer, and only daily rainfall totals, not hourly totals, were selected for use in this study. Because the Governor presented his prayer on the steps of the capitol in Atlanta and he was especially concerned with that city and the surrounding area, I decided to use rainfall data from one site--the Atlanta Hartsfield International Airport. Rain is collected and measured at numerous sites in and around Atlanta, but I thought that the data from the airport site would be as good or better than the data from the other sites since accurate weather information is essential to the safety of airline traffic.

I obtained daily rainfall totals from a well-respected website, The Weather Source, (3) for a time period of a little more than ten years from August 30, 1997 through January 27, 2008. There were no missing data points for this time period. The daily rain totals from the website are reported to the nearest hundredth of an inch, and for some days a "T" is recorded to indicate a "trace amount." In order to ensure that every day had a numerical value, each "T" was converted to ".005" inches.

The total amount of rain during any 48-day period was calculated by simply summing the daily totals for the time period. Thus, the amounts of rainfall during the 48-day pre-prayer period (A) and during the 48-day post-prayer period (B) were determined. From these two numbers, two change scores were then calculated: (1) the amount of rain in the post-prayer period minus the amount of rain in the pre-prayer period (B-A), and (2) the percent change in the amount of rainfall from the pre-prayer to the post-prayer period (100 (B-A)/A).

Similar calculations were made for "control days," which were defined as days within about the last ten years on which Mr. …