A cure for cancer?

In 1949, the Gallup Poll asked "Do you think a cure for cancer will be found in the next fifty years?"  88% thought that a cure would be found, and only 7% did not.  The same basic question has been asked a number of times since then with only minor differences in wording, but with time horizons varying from 10 years to a century.  I estimated the relationship between the time horizon and the percent agreeing (the reciprocal seemed to give the best fit--that is, going from 10 to 20 years made about as much difference as going from 50 to 100).  The adjusted percentages of people agreeing (as a percentage of those who agreed or disagreed) are shown in the figure.  The adjustment estimates the percent that would have agreed if the question had asked about the next 50 years.  There is a definite downward trend, but a substantial majority still expects to see a cure.