An experiment was conducted to investigate whether a graphologist (a handwriting analyst) could distinguish a normal person’s handwriting from that of a psychotic. A well-known expert was given 10 files, each containing handwriting samples from a normal person and from a person diagnosed as psychotic, and asked to identify the psychotic’s handwriting. The graphologist made correct identifications in 6 of the 10 trials (data taken from Statistics in the Real World, by R. J. Larsen and D. F. Stroup [New York: Macmillan, 1976]). Does this evidence indicate that the graphologist has an ability to distinguish the handwriting of psychotics? (Hint: What is the probability of correctly guessing six or more times out of 10? Your answer should depend on whether this probability is relatively small or relatively large.)
Continuous Probability Distributions
Probability distributions are of two types, which are continuous probability distributions and discrete probability distributions. A continuous probability distribution contains an infinite number of values. For example, if time is infinite: you could count from 0 to a trillion seconds, billion seconds, so on indefinitely. A discrete probability distribution consists of only a countable set of possible values.
Normal Distribution
Suppose we had to design a bathroom weighing scale, how would we decide what should be the range of the weighing machine? Would we take the highest recorded human weight in history and use that as the upper limit for our weighing scale? This may not be a great idea as the sensitivity of the scale would get reduced if the range is too large. At the same time, if we keep the upper limit too low, it may not be usable for a large percentage of the population!
An experiment was conducted to investigate
whether a graphologist (a handwriting analyst) could distinguish a normal person’s handwriting from that of a
psychotic. A well-known expert was given 10 files, each
containing handwriting samples from a normal person and
from a person diagnosed as psychotic, and asked to identify
the psychotic’s handwriting.
The graphologist made correct identifications in 6 of the
10 trials (data taken from Statistics in the Real World, by
R. J. Larsen and D. F. Stroup [New York: Macmillan, 1976]).
Does this evidence indicate that the graphologist has an
ability to distinguish the handwriting of psychotics? (Hint:
What is the probability of correctly guessing six or more
times out of 10? Your answer should depend on whether this
probability is relatively small or relatively large.)
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