Our main outcome is periodontal disease and our cohort will be asked if they have been told to have periodontal disease every year for 5 years.

To evaluate smoking history as a risk factor for developing periodontal disease we will conduct a nested case-control study.  With this type of study design we can eliminate recall bias commonly found in case-control studies; cases and controls are more comparable as they come from the same cohort.

Our target population is all adults between 30 years old and 64 years old and our source population will be from a cohort study that includes smoking status in the baseline characteristics of the population, i.e the Atherosclerosis Risk in Communities Study (ARIC), US national registries.

Exposure will be defined as smoker or nonsmoker.  This exposure is included in the baseline characteristics of our cohort.  By the time a case is identified it will be review from the baseline characteristics if they have smoking history.

The main comparison groups of participants in the study will be persons with periodontal disease (cases) and persons without periodontal disease (controls).  With every case identified, there will be 2 controls selected from the same cohort that have not develop the disease in that period.

Our main outcome is periodontal disease and our cohort will be asked if they have been told to have periodontal disease every year for 5 years.

In nested case control studies, it is not possible to identify the incident rate, cumulative incidence or prevalence, as our control is a group of the cohort and don’t represent the entire population.

Odds Ratio (OR) will be used for our association measure as we can’t calculate incidence in case-control studies; we will find how more often is smoking in periodontal disease than nonsmokers.

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