(a) C. The data were obtained at a specific point in time, and the study was an observational study.
(b) OB. Whether a person has gum disease or not. The variable of interest is qualitative as it categorizes individuals based on the presence or absence of gum disease.
(c) The estimated proportion of individuals with sleep apnea who have gum disease with a 99% confidence interval is: between 0.528 and 0.668.
(a) The study being cross-sectional means that data was collected at a specific point in time rather than over a period. Additionally, it was an observational study, meaning that researchers observed and analyzed existing data without intervention or manipulation of variables.
(b) The variable of interest in this study is whether a person has gum disease or not. It's qualitative because it categorizes individuals into groups based on the presence or absence of gum disease, rather than assigning numerical values.
(c) Estimating the proportion of individuals with sleep apnea who have gum disease involved calculating a confidence interval. With 99% confidence, it's estimated that between 52.8% and 66.8% of individuals suffering from sleep apnea have gum disease based on the sample data. This interval provides a range where we are 99% confident the true population proportion lies.