Question

blood is classified by blood type (either a, b, ab or o) and by rh - level as either rh+ or rh-. a phlebotomist classified the blood type and rh - level of the blood of 500 individuals. the data obtained are shown in the contingency table below.

	blood type
rh -	30	4	12	30	76
rh+	176	22	28	198	424
total	206	26	40	228	500

which of the following is the marginal distribution of rh - level?

rh- = 30/76, rh+ = 176/424

rh- = 76/500, rh+ = 424/500

rh- = 30/500, rh+ = 176/500

rh- = 424/500, rh+ = 76/500

Explanation:

Step1: Recall marginal - distribution concept

The marginal distribution of a categorical variable in a contingency table is found by dividing the row - totals (or column - totals) by the grand total. For the Rh - level variable, we want to find the proportion of Rh - and Rh+ in the entire sample.

Step2: Identify relevant totals

The total number of individuals with Rh - is 76 and the total number of individuals with Rh+ is 424. The grand total of all individuals in the sample is 500.

Step3: Calculate marginal probabilities

The probability of an individual being Rh - is $\frac{76}{500}$ and the probability of an individual being Rh+ is $\frac{424}{500}$.

Answer:

Rh- = 76/500, Rh+ = 424/500