sentences:  also raised concerns about other flaws in the study, such as misclassification of laws and endogeneity of predictor variables, which they said rendered the study's conclusions "insupportable".Florida State University criminologist Gary Kleck considered it unlikely that such a large decrease in violent crime could be explained by a relatively modest increase in concealed carry, and others said that removing portions of the data set caused the results to still show statistically significant drops only in aggravated assaults and robbery when all counties with fewer than 100,000 people and Florida's counties were both simultaneously dropped from the sample.A 1998 study by Jens Ludwig that said it "more effectively control[ed] for unobserved variables that may vary over time" than the Lott and Mustard study concluded that "shall-issue laws have resulted, if anything, in an increase in adult homicide rates."