Differential privacy of "randomized responses" We define randomized responses as follows:


  In a question that can be responded with a "Yes" or "No", a respondent is asked to flip a fair coin, in secret, and answer the truth if it comes up tails. Otherwise he/she flips another coin in secret, and answers "Yes" if comes up tails, "No" otherwise.


According to the introduction this paper [1], the $\epsilon$-differential privacy of surveys relying on randomized responses is:
$$
\ln(0.75/(1-0.75)) = \ln(3)
$$
I am wondering how was this calculated. Note that the proofs contained in paper are related to the RAPPOR protocol.

[1]Úlfar Erlingsson, Vasyl Pihur, Aleksandra Korolova,"RAPPOR: Randomized Aggregatable Privacy-Preserving Ordinal Response"  https://research.google.com/pubs/archive/42852.pdf
I found the answer in this book  https://www.cis.upenn.edu/~aaroth/Papers/privacybook.pdf at page 30


  Fix a respondent. A case analysis shows that 
  $$Pr[Response = Yes|Truth = Yes] = 3/4$$ 
  Specifically, when the truth is “Yes” the
  outcome will be “Yes” if the first coin comes up tails (probability
  1/2) or the first and second come up heads (probability 1/4),
  while $$Pr[Response = Yes|Truth = No] = 1/4$$ (first comes up heads and
  second comes up tails; probability 1/4). Applying similar reasoning to
  the case of a “No” answer, we obtain:
  $$
\frac{Pr[Response = Yes|Truth = Yes]}{Pr[Response = Yes|Truth = No]}=
\frac{3/4}{1/4}= \frac{Pr[Response = No|Truth = No]}{ Pr[Response = No|Truth = Yes]} = 3$$