A note to the teacher: To help doctors or researchers determine critical ages in which fractures occur, many studies have been conducted on men and women. Doctors are anxious to figure out when the risk of fracture is highest. In order to do this, the researchers have to take information and turn it into something that has meaning. The students are going to have a chance to figure fracture rates from the data collected in a study conducted in Canada. The authors of this study gathered data on the incidence of hip fractures in Saskatchewan Canada, residents aged 65 years or older for the 10 years between 1976-1985 from computerized hospital discharge records and compared it with rates for several other populations in Northern Europe and the United States. This study was restricted to people 65 years or older because this is the population group for which hipfracture has the greatest public health impact. The data used in this activity is taken from: Ray, W.A., M. R. Griffen, R. West, L. Strand, and L. J. Melton III. "Incidence of Hip Fracture in Saskatchewan, Canada 1976-1985," American Journal of Epidemiology 1990; 131: 502-9.
In this lesson, explain fractures to students. Fractures are breaks or cracks in a bone. Point out that in older adults these breaks usually occur in the hip, wrist, or vertebrae areas. In older persons, fractured bones are often due to decreased bone mineral density. That is, the lower the bone density, the greater the risk of breaking a bone (for example, during a fall).
The Fracture rate is a ratio of the number of fractures in a group of people over a given period of time. These ratios can be used to calculate the probability that a fracture will occur. This is important for doctors to know so that they can track the ages at which fracture is most probable.
Hand out the worksheet, "Figuring Fracture Rate." The students should follow along as you explain the given information. The doctors in this study only looked at adults that had fractures occurring in the hip area. They kept up with this information for ten years. So, in the column labeled, # Fractures, the number represents how many fractures occurred in that age group over a ten year period. Ask students how many fractures occurred in women between the ages of 65-69. They should respond with 347.
The next column, Person Years, is the amount of time of exposure to the potential event experienced by the people in the study. Person years is calculated by taking the total number of people in the study multiplied by the number of years they were in the study. So if 10 people stayed in the study for 10 years, then it would equal 100 person years; or if 50 people were studied for 2 years, it would also equal 100 person years. How many person years are in women between the ages of 85-89? Answer: 44,141.
Now to calculate the rate of fractures for every 1,000 person years, the student should divide the number of fractures by the total person years (e.g., 347 / 95,647 = 0.0018), and then multiply by 1,000 (0.0018 x 1,000=1.8). Work this one out on the board with the students. Instruct the students to complete the worksheet for both men and women.
Fracture rate, calculation, population statistic
