I am having trouble in my EPIDEMIOLOGY class with ratio and proportion . I think

Question

I am having trouble in my EPIDEMIOLOGY class with ratio and proportion. I think I understand ratio but how do you calculate proportion? This is one of my homework questions (I answered a):

1.     During the first 9 months of national surveillance for eosinophilia-myalgia syndrome (EMS), CDC received 1,068 case reports which specified sex; 893 cases were in females, 175 in males.

     a. What is the female-to-male sex ratio of cases? Describe your findings.

893 females/175 males = 5.10

Ratio is approximately 5 females for every 1 male

         b. What proportion of the EMS cases are male?

     c. What hints to etiology does this information provide?

Explanation / Answer

To calculate the female­to male ratio:

1. Define x and y: x = cases in females and y = cases in males

2. Identify x and y: x = 893 and y = 175

3. Set up the ratio x/y: 893/175

4. Reduce the fraction: 5.1 to 1 (5 to 1)

Thus, there were 5 female EMS patients for each male EMS patient reported to CDC.

To calculate the proportion of EMS cases that is male:

1. Define x and y: x = cases in males and y = all cases

2. Identify x and y: x = 175 and y = 1,068

3. Calculate the proportion x/y: 175/1,068

4. Reduce the fraction and *100: 0.16*100

0.16 * 100 = 16%

Thus, 16% of the reported EMS cases were males.

In the first example, we calculated the female-to-male ratio. In the second, we calculated the proportion of cases that were male. Is the female-to-male ratio a proportion? The female-to-male ratio is not a proportion, since the numerator (females) is not included in the denominator (males), i.e., it is a ratio, but not a proportion

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