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Lab K An exercise in experimental design and implementation.

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Presentation on theme: "Lab K An exercise in experimental design and implementation."— Presentation transcript:

1 Lab K An exercise in experimental design and implementation

2 Between-subjects designWithin-subjects design -each person in the lab would be assigned to one of the four treatments using random allocation (eg. rolling a fair die and ignoring two of the faces, generating random numbers in minitab and ignoring all but digits 1, 2, 3 and 4, etc.) - Randomisation is used so that there are no systematic differences between the people allocated to different treatments – i.e. it attempts to control for potential confounding variables -each person in the lab would be asked to perform the experiment under each of the conditions, i.e. four times - randomization would be used to assign participants to a particular order of the treatments, thereby counterbalancing the design to minimize the potential order-effects acting as a confounding factor

3 Between-subjects designWithin-subjects design Advantages and disadvantages + only requires each participant to do the experiment once, thereby saving time + potential order effects (eg. fatigue, practice, crossover effects) are avoided and do not need to be controlled for in the design + the subsequent analysis is straight forward, as there are four independent groups to compare + the randomization is relatively straight forward - would require a larger number of participants to get adequate numbers in each treatment group Advantages and disadvantages -requires each participant to do the experiment four times, thereby needing a lot of time -introduces potential order effects (eg. fatigue, practice, crossover effects) which the design should carefully consider in order to minimize the potential effects (i.e. lag between experiments) -the subsequent analysis is complex, involving the analysis of repeated measures + more powerful to detect treatment differences, since effects of individuals are controlled + would require a relatively small number of participants to get reliable results for each treatment level

4 Suggested design and why Given our limited numbers in the lab group, we would favour the within-subjects design, notwithstanding the additional work involved in the randomization and the analysis.

5 To make a Latin square… 1.Create a random order of the levels, (e.g. BACD for a four-level IV) 2.Sequentially number the levels in this random order starting with 1. (e.g. B=1, A=2, C=3 and D=4) 3.To create the first order in the Latin square, put the last number/level in the 3rd position, (e.g. 1, 2, 4, 3). If we had more than four levels, N say, then every subsequent unevenly numbered position (e.g. 5, 7, and so on) would have one less than the previous unevenly numbered position as shown in the following table. Order number Level12N3N-14N-25N-36

6 Labeling of the treatment levels in the random order 1 = C 2 = D 3 = B4 = A Latin Square of labels Latin square of treatments 1243Order 1CDAB 2314Order 2DBCA 3421Order 3BADC 4132Order 4ACBD

7 Random allocation to orders

8 Series 1

9 baboon

10 peanut

11 locust

12 carpet

13 glider

14 fleece

15 almond

16 cymbal

17 jackal

18 bikini

19 chisel

20 pepper

21 budgie

22 sandal

23 coyote

24 Series 2

25 badger

26 raisin

27 maggot

28 cooker

29 rocket

30 jacket

31 banana

32 fiddle

33 jaguar

34 blazer

35 hammer

36 potato

37 canary

38 sarong

39 donkey

40 Series 3

41 beaver

42 tomato

43 slater

44 fridge

45 sledge

46 jumper

47 cherry

48 guitar

49 lizard

50 blouse

51 roller

52 radish

53 condor

54 shorts

55 ferret

56 Series 4

57 cougar

58 walnut

59 spider

60 heater

61 sleigh

62 mitten

63 orange

64 violin

65 monkey

66 braces

67 shovel

68 sprout

69 cuckoo

70 slacks

71 gerbil


73 Series 1 baboon peanut locust carpet glider fleece almond cymbal jackal bikini chisel pepper budgie sandal coyote

74 Series 2 badger raisin maggot cooker rocket jacket banana fiddle jaguar blazer hammer potato canary sarong donkey

75 Series 3 beaver tomato slater fridge sledge jumper cherry guitar lizard blouse roller radish condor shorts ferret

76 Series 4 cougar walnut spider heater sleigh mitten orange violin monkey braces shovel sprout cuckoo slacks gerbil


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