CRITICAL THINKING 8. CAUSAL ARGUMENTS

Transcription

1 CRITICAL THINKING 8. CAUSAL ARGUMENTS

2 Causal statements are everywhere. Water dissolves sugar. = Water causes sugar to dissolve. (Dissolving is an effect of water on sugar.) 2

3 CAUSAL CHAINS X causes Y, which causes Z. (X Y Z) X causes Z by causing Y. Playing with his smartphone distracted Bob in class, which made him fail the course. 3

4 PREVENT = CAUSE NOT A prevents B = A causes B to not happen Playing with his smartphone prevented Bob from learning. = Playing with his smartphone 4

5 Seatbelts prevent traffic accident fatalities. Seatbelts cause Salt causes 5

6 Imagine a causal chain. 1) Abby missed her plane causes B causes C. 2) Bob put out the fire prevents Y prevents Z. 6

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8 CAUSAL SUFFICIENCY AND NECESSITY X causes Y. X sufficient for Y when necessary conditions exist. What causes the match to light? NC:? X causes Y, but only if [NC]. Not-NC prevents Y even if X. 8

9 CAUSING, PREVENTING; SUFFICIENCY CONDITIONS, NECESSARY CONDITIONS Want to cause E? Want to prevent E? SUFFICIENT CONDITION E NECESSARY CONDITION E 9

10 1) Convert into an explicit causal statement. 2) Give a necessary condition. 1) The music makes Abby happy. 2) Worms attract fish. 3) The thrown rock breaks the window. 4) The civil war creates a million refugees. 10

11 CAUSE AND EFFECT 1) Write one causal statement twice. a) With regular words (not cause, is caused by, etc.). b) Explicit causal statement (with cause, is an effect of, etc.). 2) Label the cause (C) and the effect (E). 3) Give a necessary condition for the effect, and write the statement a third time to include this condition. 11

12 JOHN STUART MILL 12

13 E What caused effect E?? No E 13

14 120% What caused effect E? 100% 80% E E No E 60% 40% 20% 0% 14

15 Reconstruct the argument. Write the conclusion as an explicit causal statement. Write and number the implicit statement. Put the argument in standard form and diagram it. After their old coach left last year, the team fell way behind, from one of the best in the league to one of the worst 1. The change of coach must be why they ve performed so poorly this year 2, since they haven t lost any of their good players 3, and there have been no major changes in the other teams in the league 4. 15

16 Write a method of difference causal argument in extended form for this conclusion: Lyle s girlfriend dumped him because [was an effect of] he forgot to do the laundry this week. 16

17 A CORRELATED WITH B : POSSIBLE EXPLANATIONS A B X s B A B A A B C B A Non-A 17

18 Among children, playing violent video games is positively correlated with violent behaviour. Possible explanations: 40% 35% 30% 25% Children Violent 1) 2) 3) 4) 20% 15% 10% 5% 0% Plays violent video games No violent video games Dependent Variable (Measured Feature) Manipulated (Independent) Variable Experimental Group Control Group 18

19 What are some possible confounding variables? Children Confounding variable = other relevant difference Violent Plays Violent VG F Violent Behaviour PVVG? G VB Plays violent video games F G No violent video games Non-F Non-G 19

20 Among countries, having vaccination programs is negatively correlated with having outbreaks of infectious disease. 80% 70% Countries Possible explanations: 60% 50% 40% 30% Has disease outbreaks 1) 2) 20% 10% 3) 0% Has vaccination programs No vaccination programs 4) 20

21 What explanation of the correlation would you expect to be true? 1) There s a correlation between car accidents and snowy weather, so car accidents make it snow. 2) There s lightning more often when there is rain than there is when there is no rain. This shows that rain produces lightning. 3) A review of the data shows that meteors hit Earth on Wednesdays more often than on other days. Apparently Wednesdays bring meteors to Earth. 21

22 4) People with hearing damage are more likely to listen to heavy metal music. I guess hearing damage leads people to listen to heavy metal. 5) All three of the college instructors I ve met are jerks, but most other people aren t jerks, so being a college instructor must somehow turn people into jerks. 6) Regular exercise seems to motivate people to eat healthily, since people who exercise regularly tend to eat more healthily than other people. 22

23 ACCIDENTAL Zombies CORRELATION? 35% 30% 25% Enjoy Poetry 20% 15% 29% of zombies that eat brains enjoy poetry (±6 pts). 10% 24% of zombies that do not eat brains enjoy poetry (±4.9 pts). 5% 0% Eat Brains Don't Eat Brains Zombies that eat brains are more likely to enjoy poetry.

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25 B A? Smoking is correlated with lung cancer. Turning the key is correlated with the car starting. 25

26 25% People 20% 15% 10% Gets lung cancer 5% 0% Smokes Does Not Smoke 26

27 Step 1: Think of (or find) a possible confounding variable (possible common cause). Step 2: Control for it. ELIMINATING A COMMON CAUSE EXPLANATION Anxiety (stress) Smoking? Lung Cancer 27

28 25% People 20% 15% 10% Gets lung cancer 5% 0% Smokes Does Not Smoke 28

29 People New control group: Non-smokers Same % with anxiety Has Anxiety Smokes Does Not Smoke 29

30 100% People 80% 60% 40% Gets lung cancer 20% 0% Smokes Does Not Smoke 30

31 25% People Common cause explanation eliminated supported. 20% 15% 10% 5% Gets lung cancer 0% Smokes.(N% with anxiety) Does Not Smoke (N% with anxiety) 25% People Common cause explanation eliminated supported. 20% 15% 10% Gets lung cancer 5% 0% Smokes.(N% with anxiety) Does Not Smoke (N% with anxiety) 31

32 100% 90% Children In children, violent behaviour is positively correlated with playing violent video games. 80% 70% 60% 50% 40% 30% Violent Confounding variable (possible common cause): Having a violent older brother (VOB). 20% 10% 0% Plays violent video games.(n% w/vob) No violent video games.(n% w/vob) New control group: No VVG. Same % with VOB. 32

33 Children Children 40% 40% 35% 35% 30% 30% 25% 20% Violent 25% 20% Violent 15% 15% 10% 10% 5% 5% 0% Plays violent video games.(n% w/vob) No violent video games.(n% w/vob) 0% Plays violent video games.(n% w/vob) No violent video games.(n% w/vob) 33

34 We discovered this positive correlation: most plants that are fed Super Plant Grow TM plant food grow fast, whereas most plants that are not fed SPG do not grow fast. Therefore SPG makes plants grow fast. Describe an alternative explanation for the correlation. Common cause explanation. Use at least one causal chain to make the explanation clear. Describe how you could test this explanation with a controlled experiment. 34

35 Look for best plant food Plants fed SPG. CPO Give water/light to plants Plants grow fast. 35

36 RCT Experimental group: Gets SPG Control group: No SPG 36

37 A NEW PROBLEM 70% 60% 50% 40% 30% 20% 10% 0% People with Disease D M chemicals in blood No M chemicals Gets healthy Experimentally Introduced Confounding Variable 37

38 TASTE TEST! 1947 Château Cheval Blanc (Bottle: US$304,375) 2016 Franzia White Zinfandel (5 litre box: $12.99) 38

39 ? Gets Healthy 70% 60% 50% 40% 30% 20% 10% 0% People with Disease D M chemicals in blood No M chemicals Gets healthy 39

40 70% People with Disease D NEW CONTROLLED 60% 50% 40% 30% 20% 10% Gets healthy EXPERIMENT New Control Group: Placebo control No M chemicals 0% M Chemicals No M Chemicals Same beliefs/expectations 40

41 People with D 70% 60% 50% 40% Gets healthy 30% 1) Same correlation 20% 10% Placebo effect eliminated supported. 0% M Chemicals No M Chemicals 41

42 People with D 70% 60% 50% 40% Gets healthy 30% 2) No correlation 20% 10% Placebo effect eliminated supported. 0% M Chemicals No M Chemicals 42

43 People with D 70% 60% 50% 40% Gets healthy 3) Reduced correlation 30% 20% pts difference reduced to pts difference. 10% 0% M Chemicals No M Chemicals % of the original effect explained by a placebo response. 43

44 We wondered whether running smartphones CPUs hard would prevent their batteries from lasting a full day, so we did an RCT experiment. We randomly assigned smartphones to a CPU run hard group and a control group. To run the CPUs hard, we had people play Game G, which uses the CPU a lot. We found a negative correlation between running the CPU hard and the battery lasting all day. Therefore we conclude that running the CPU hard prevents the battery from lasting all day. Think of a possible confounding variable, and describe an alternative explanation of the data. Draw a cause-and-effect diagram. Describe how to test this alternative explanation. 44

45 Game G CPU works hard? Long battery life Phone held tightly Phone heats up Experiment: Control for being held tightly (or for heating up) and check again. New control group: No CPU works hard. Phones held tightly (or heated up). 45

46 Identify the problem(s) and describe how to fix them. Causal Argument (Ver.1) I [a wealthy guy] surveyed five of my friends who do feng shui, and I found that 60% (3/5) of them are wealthy. So 60% of people who do feng shui are wealthy. So doing feng shui makes people wealthy. [Identify statistical problems only.] 46

47 Causal Argument (Ver.2) I surveyed 500 randomly selected people who do feng shui, and I found that 60% (300/500) of them are wealthy. So 60% of people who do feng shui are wealthy. So doing feng shui makes people wealthy. 47

48 Causal Argument (Ver.3) In a random sample of 500 people who do feng shui, 60% (300/500) are wealthy. And in a random sample of 570 people who do not do feng shui, only 30% are wealthy. So doing feng shui causes people to be wealthy. 48

49 Causal Argument (Ver.4) 1000 people were randomly assigned to either a feng shui group (n=520) or a nonfeng shui group (n=480). After 10 years, 60% of the feng shui group were wealthy but only 30% of the non-feng shui group were wealthy. So doing feng shui makes people wealthy. So magical qi energy flows through people s homes and brings them wealth if it is properly directed. 49

50 Abby notices that several friends who read the textbook for the course they are in do well in that course. She thinks to herself: I guess reading the textbook makes people do well in this course. 1) Restate Abby s conclusion as an explicit causal statement. 2) State one necessary condition for this causal statement. 3) Using relevant concepts from this course, describe the minimum (simplest) experiment that Abby would need to do to support her conclusion. 4) Imagine that Abby s experiment supports her conclusion. Draw a bar chart. 50

51 5) Think of a possibly confounding variable, and describe an alternative common cause explanation of Abby s data. Draw a simple cause-and-effect diagram. 6) Briefly describe a new experiment that could eliminate this explanation. Abby s new experiment supports her conclusion. She thinks: I know that reading the textbook makes people remember more information, and textbook-readers do well more often than non-textbook-readers, so I guess remembering more information makes people do well in the course. 7) Think of a possible confounding variable introduced by Abby s experiment. (Your suggestion does not have to be plausible [believable].) 8) Briefly describe an improved experiment. 51