Problem 3: Renal Failure and Three Occupational Exposures A study to examine the

Question

Problem 3: Renal Failure and Three Occupational Exposures A study to examine the association between renal failure and occupational exposure to metal fumes, solvents and silica was conducted. The study included 325 people with renal failure, age 36 to 69 at diagnosis. A comparison group of 325 healthy people from the general population of the same city was chosen via random-digit telephone dialing. From those with renal failure: 119, 124 and 87 were determined to.have.been exposed to metal fumes, solvents and silica respectively. Among the comparison group, the numbers exposed were 96, 82 and 54 respectively. ine 124 an 87 wer dined to have been eod 1) Choose the measure of association most appropriate for this study design, and then calculate the association between each of the three exposures and the outcome. Show all steps in your calculations, including your 2 by 2 table for each calculation. Calculation #1 : Calculation #2 Calculation #3:

Explanation / Answer

1)

Measure of association is chi square coefficient. Using which we can find p-value to check if the association is significant or not.

By default, the null hypothesis is there is no association between exposure and renal failure.

3)

Calculate the expected value for each of the cells by the formula

expected value of a cell = row total of the cell * column total of the cell/ grand total

calculate the chi square for each of the cell by (observed value - expected value)/expected value

          0.11

Calculate the sum of the 6 cells to find the chi-square i.e. 1.71

probability of (chisquare value greater than 1.71 for 2 degree of freedom) is p-value

p-value for 2 degrees of freedom ( (row-1)* (col-1) ) is 0.42

4)

contribution to chisquare

since the contribution is high for metals and low for other two.

Metals - strong

Solvents - weak

Silica - weak

5)

since p-value is greater than 0.05 donot reject null hypothesis.

Hence there is some association between exposure and renal failure.

observed renal healthy metal 119 96 215 solvents 124 82 206 silica 87 54 141 330 232 562

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