8.3 Calculating heritability for threshold traits (diseases)

The calculations are based on disease frequencies in the general population (Population) and among relatives (Indiv. related ) to a diseased animals. The relatives can be (both parents diseased), first degree (father, mother or full sibs) or second degree (half sibs or grand parents).Remember only one type of relatives can be analyzed at the same time.

Degree of relation ->
Set digit for print ->

Observe: The chi-square test calculation is based on: that the related ones is subtracted from the population numbers!

Enter your observed numbers and degree of relationship and then press the Calculate button. The values in the (Degree of relationship) field should 1, .5 and .25 for the three above mentioned cases.
You can also enter the frequencies but then the numbers shall be zeros in the observed number fields.
Illustration of the case where both parents are affected are given below. The program is initiated with the actual data for frequencies and the "Degree of relationship" is set to 1 (both parents diseased); to see Press the Calculate button and see the results corresponding to the figure below.

Remember in case of first or second degree relative analyses with half or full sib, one affected individual per family is an index case and should be subtracted from the group 'individual related'. So if there are 10 families with at least one affected in the population, 10 affected should be subtracted.

In the table below is given observed numbers for disease frequencies in the population and in first-degree relatives to diseased animals.
              Normal  Diseased  Frequency
Population      980       20        0.020
relative        140       10        0.066

Estimate the heritability.
What is the relative risk to be related to a diseased animal ?
Is the heritability statistically significant different from 0 with (p< 0.05) ?

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