Example of Contingency Table and use of tablerxc.m m-file.
Example of Contingency Table and use of tablerxc.m m-file.
Example of Contingency Table and use of tablerxc.m m-file.
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BMED 2803Brani VidakovicThursday 3/29/2007<strong>Contingency</strong> <strong>Table</strong> <strong>Example</strong>Importance <strong>of</strong> byst<strong>and</strong>ers. Darley <strong>and</strong> Latané (1968) 1 asked subjects to participate ina discussion carried over an intercom. Aside from the experimenter to whom they werespeaking, subjects thought that there were zero, one, or four other people (byst<strong>and</strong>ers) alsolistening over intercom. Part way through the discussion, the experimenter feigned seriousillness <strong>and</strong> ask for help. Darley <strong>and</strong> Latané noted how <strong>of</strong>ten the subject sought help for theexperimenter as a function <strong>of</strong> the number <strong>of</strong> supposed byst<strong>and</strong>ers. The data are given in thetable:Sought Assistance No AssistanceNo byst<strong>and</strong>ers 11 2One byst<strong>and</strong>er 16 10Four byst<strong>and</strong>ers 4 9What could Darley <strong>and</strong> Latané conclude from the results?• State H 0 <strong>and</strong> H 1 .• Perform the test at 5% significance level. Use matlab.[Sol. H 0 : Assistance <strong>and</strong> the number <strong>of</strong> byst<strong>and</strong>ers are independent. Here is theMINITAB (which is available in the Lab) output.C1 C2 TotalR1 11 2 137.75 5.25R2 16 10 2615.50 10.50R3 4 9 137.75 5.25Total 31 21 52ChiSq = 1.363 + 2.012 +0.016 + 0.024 +1.815 + 2.679 = 7.908df = 21 Darley, J. M. & Latane, B. (1968). Byst<strong>and</strong>er intervention in emergencies: Diffusion <strong>of</strong> responsibility.Journal <strong>of</strong> Personality <strong>and</strong> Social Psychology, 8(4), 377-383.1
Matlab output from <strong>tablerxc</strong>.m>> [ch2, pval, exp]=<strong>tablerxc</strong>([11 2; 16 10; 4 9])ch2 = 7.9078pval = 0.0192exp =7.7500 5.250015.5000 10.50007.7500 5.2500Drinking trends on Duke campus. Stereotypically, drinking <strong>and</strong> partying have alwaysbeen synonymous with college life. Recently, this has been a controversial issue at DukeUniversity beca<strong>use</strong> <strong>of</strong> the implementation <strong>of</strong> the alcohol policy. As the result <strong>of</strong> the alcoholpolicy, fraternities are no longer permitted to openly distribute alcohol to party goers.Br<strong>and</strong>ie, R<strong>and</strong>y, <strong>and</strong> Stephanie 2 decided to test how the alcohol policy, <strong>and</strong> the atmosphereit generates, affects drinking trends on the Duke campus.Part <strong>of</strong> their data includes the following table which is preference broken down by gender<strong>and</strong> type <strong>of</strong> alcohol:hard alcohol beer totalmale 20 27 47female 27 7 34total 47 34 81• (i) Test for independence <strong>of</strong> factors (gender, type <strong>of</strong> drink). Use α = 0.05.• (ii) Explain in words what constitutes the error <strong>of</strong> II kind in the above testing.2 Br<strong>and</strong>ie Littlefield, R<strong>and</strong>y Savino, <strong>and</strong> Stephanie Weiss: An analysis <strong>of</strong> the drinking trends on Dukecampus, STA110E Project, Fall 1995.2
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