Question

An import threshold for mercury in crayfish. What is the test statistic for this problem?

An import threshold for mercury in crayfish is 9 parts per billion (ppb). A study, obtained a random sample of 120 crayfish from a large lake. Of these, 24 have levels of mercury that exceeded 9 ppb. Past research had shown that 25% of the crayfish had levels that exceed 9 ppb. The researchers wanted to see if there was a change in contamination in crayfish. What is the test statistic for this problem? (use 2 decimal places)? 1.26 -1.37 -31 - 1.26

Answer 1

Answer:

single sample proportion test

Ho: P=0.25, H₁: P≠0.25

p=24/120=0.2

$z = \frac{ p - P}{\sqrt{ P*(1-P)/n}}$

$z = \frac{ 0.2 - 0.25}{\sqrt{ 0.25 *(1- 0.25)/120}}$

= -1.26

Answer: -1.26

Z Test of Hypothesis for the Proportion
Data
Null Hypothesis            p =	0.25
Level of Significance	0.05
Number of Items of Interest	24
Sample Size	120
Intermediate Calculations
Sample Proportion	0.2
Standard Error	0.0395
Z Test Statistic	-1.2649
Two-Tail Test
Lower Critical Value	-1.9600
Upper Critical Value	1.9600
p-Value	0.2059
Do not reject the null hypothesis