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When studying animal behavior, the distribution of organisms within a choice chamber can be studied to identify animal preferences. 20 Isopods are placed in a 2-choice choice chamber. A cotton ball dampened with distilled water is placed in Chamber A; A dry cotton ball is placed in Chamber B. After 15 minutes 2 Isopods are located in Chamber B, and 18 isopods are found in Chamber A. Perform the chi-squared test to determine if the distribution of isopods is significant or due to random chance.a. chi-squared is 1.20, no it is not significant.

b. chi-squared is 8.42, no its not significant.c. chi-squared = 12.8, yes it is significant.d. chi-squared is 18.59, yes it is significant.

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Answer:

The correct option is c. chi-squared = 12.8, yes it is significant.

Explanation:

Available data:

  • 20 Isopods are placed in a 2-choice choice chamber.
  • Different conditions were applied
  • 15 minutes later: 18 isopods are found in Chamber A and 2 Isopods are located in Chamber B.

H₀= Individuals will be equally distributed  

H₁ = Individuals will not be equally distributed.  

  • Chi square= ∑ ((O-E)²/E)  

∑ is the sum of the terms

O are the Observed individuals: 2 in chamber B, and 18 in chamber A.  

E are the Expected individuals: 10 in each chamber  

X² = ∑ ((O-E)²/E) = ((2 - 10)²/10) + ((18 - 10)²/10) = 6.4 + 6.4 = 12.8  

X² = 12.8  

  • Freedom degrees = K – 1 = 2 - 1 = 1  

(K = Independent variables = dry cotton and wet cotton)  

  • Significance level, 5% = 0.05  
  • Table value/Critical value = 3.84  

12.8 > 3.84 meaning that the difference between the observed individuals and the expected individuals in each chamber is statistically significant. Not probably to occur by random chances.  

  • There is enough evidence to reject the null hypothesis.  
  • The distribution of isopods is statistically significant.

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