Reasoning and Decision Making How reliable is vision How reliable is vision 1 How good is human reason Behind one of these doors I have hidden money behind the other two a cat You get to pick which one to open But before you open it I will open one of the other doors revealing a cat Now I give you a choice stay with you first pick or change to the other Which is the better option http www shodor org interactivate activities monty3 A Bad Doctor s Visit You go to see your doctor with a puzzling ailment Your doctor tells you that it is characteristic of a disease that that is affecting 1 of the population and if you have it it means certain death There is a simple test she can perform which is accurate 79 of the time that is 21 of the time it gives false positives You agree to the test Now your doctor looks really worried The test came back positive How worried should you be How likely are you to die Answer your risk of death is 8 When is evidence diagnostic Data from 250 patients Is dizziness associated with brain tumors Which information is relevant Brain tumor Dizziness Present Absent Present 160 40 Absent 40 10 2 Sensible Policy Making You are a member of the health commission and must choose between these two policies Program A 200 people will be saved 72 Program B 1 3 chance of saving 600 people and 2 3 chance of saving no one You are on the disaster management board and must choose one of two options Program C 400 people will die Program D 1 3 chance that no one will die and 2 3 chance 78 that 600 people will die Exemplary Reasoning in Science Heredity Prior to Mendel The basic idea that offspring are similar to their parents had been obvious to people for ages It also was clear that offspring varied from their parents Animal and plant breeders capitalized on these differences By controlling mating and eliminating undesired organisms breeders were able to produce plants and animals with desired traits By multiply breeding offspring and eliminating variants breeders could generate pure breeds Gregor Mendel An Augustinian monk Mendel studied physics and natural science in Vienna but lived most of his adult life in the cloister at Altbrunn now Brno in the Czech Republic Starting in 1856 he conducted plant breeding experiments in the cloister s garden 3 Mendel s Breeding Experiments Choice of peas naturally self pollinated but easy to crosspollinate Mendel introduced the vocabulary of dominant and recessive characters Mendel s Procedure Cross pollinate between pure breeding lines with alternative traits yellow green smooth dented All members of the F1 generation exhibit the dominate traits Allow members of the F1 generation to self pollinate First Generation from Hybrids Form of seed Round Wrinkled 5474 1850 2 96 1 Color of albumin Yellow Green 6022 2001 3 01 1 Color of seed coat Violet flowers White flowers 705 224 3 15 1 Form of pods Inflated Constricted 822 299 2 95 1 Color of unripe pods Green yellow 428 152 2 81 1 Position of flowers Axial terminal 651 207 3 14 1 Length of stem Long short 787 277 2 84 1 4 F2 Generation Produced by self fertilization of members of the F1 generation Individuals with recessive traits bred pure One out of three of those showing the dominant character produced only offspring with the dominant character Theoretical problem for Mendel what could explain these and other patterns he found Mendel s Hypothesis Behind the characters lay factors pollen and egg cells each possessed the factor for either the dominant or recessive trait What evidence does Mendel have for these factors Only that they account for the inheritance pattern he saw and others he predicted Without his hypothesis these other predictions would not have been made YY Y yy P Yy F1 y Yy Y y Y YY Yy y Yy yy F2 Features of Mendel s Reasoning He designed a study that could reveal structure in the phenomena He found a systematic pattern in the phenomena He proposed a hypothesis that could explain the pattern He supported this hypothesis by both the pattern he initially observed and others which it predicted These patterns would otherwise be mysterious Message Successfully predicting what would otherwise be mysterious is typically the way hypotheses gain support 5