Question

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

Answer 1

Answer:

c

Explanation:

Random distribution of the Isopods should be 50/50 in A and B.

Chi-square = $\frac{(O - E)^2}{E}$ where O = observed frequency and E = expected frequency

Chamber         O                    E             Chi-square

  A                   18                   10             $\frac{(18 - 10)^2}{10}$ = 6.4

  B                    2                    10             $\frac{(2 - 10)^2}{10}$ = 6.4

Total Chi-square = 6.4 + 6.4 = 12.8

Degree of freedom = 2 - 1 = 1

Tabulated Chi-square (α = 0.05) = 3.8415

The calculated Chi-square exceeds the critical value, hence, it is significant and not due to random.

The correct option is c.