Question

A study was done to determine whether the amount of money spent on soft drinks was related to mortality from diabetes. The investigators collected data on per capita (average per person) soft drink consumption in ten US states and examined its relationship to mortality rates from diabetes in those ten states. In order to calculate per capita sales, they gathered annual data on soft drink sales from commerce records and then divided these figures by the state’s population from the most recent census. The mortality data were gathered from the vital records department in each state. Here are the data that they collected.

Question: Unfortunately, the investigators had never taken and epidemiology course and did not acknowledge any limitations of their study. Briefly describe at least two major limitations that they should have acknowledged.

US State	Annual per Capita Soft Drink Sales	Annual Diabetes Mortality Rate (per 100,000 population)
Massachusetts	$150	207
New York	$300	353
Florida	$500	688
Alabama	$700	801
Alaska	$50	75
California	$500	605
Nevada	$200	310
Idaho	$250	325
Ohio	$400	454
Arkansas	$350	405

Answer 1