Causes and effects

What is wrong with this picture? Jonathan Gruber of M.I.T. and Daniel M. Hungerman of Notre Dame studied what happens when states repeal "blue laws," that is, statutes limiting business activity on Sundays.

In their article, "The Church vs. the Mall: What Happens When Religion Faces Increased Secular Competition?" published by the National Bureau of Economic Research, they found that when blue laws are thrown out, church attendance declines and drinking and drug use go up. The effect is especially pronounced among churchgoers.

Under the blue laws, Gruber and Hungerman calculated that about 37 percent of people in those states were in church every week. But once stores were open on Sunday, the rate dropped to 32 percent. Churchgoers' marijuana use jumped 11 percent, their cocaine use went up 4 percent, and their heavy drinking went up 5.5 percent.

Hungerman speculates that when the malls are open, many religious people have to work instead of going to church, exposing them to more temptations and bad influences: "Instead of being in church, you're working or shopping in the mall surrounded by 'party animals.'"

But look more closely at the study. Which is more likely, that repealing blue laws causes more "secular" behavior? Or that more "secular" behavior caused the repeal of the blue laws?

Causality is enormously difficult to establish. One of the most common logical fallacies is post hoc ergo propter hoc ("after this; therefore, because of this"). This mistakes a relationship of time for a relationship of cause. The classic example is the little boy who kicked a telephone pole just seconds before the entire power grid on the East Coast crashed and whole cities were plunged into darkness. The boy just knew that he was to blame.

In the case of the blue law study, is there actual evidence that churchgoers are hanging out at malls with drug dealers? Might other factors contribute to the drop in church attendance and moral slippage among churchgoers? (Such as churches that in their consumerism and worldliness are becoming indistinguishable from shopping malls?)

Even when there are clear connections and correlations, though, causality is difficult to prove. Consider a study that finds that children who commit acts of violence watch more TV than other children. What does the study actually prove? That TV watching causes violence? Or does violence cause TV watching? (That is, do violent children simply enjoy TV with its violence more than peaceful children do?) Or, is watching TV all day evidence that the child is not getting enough parenting?

Keep this in mind the next time you read about a chemical that "causes" cancer (or does cancer cause the body to form the chemical?), or a brain formation that "causes" homosexuality (or does homosexuality cause the brain formation?), or a "cause" of sin other than the mystery of iniquity in the human heart.