5. A researcher is investigating the density of earth worms in garden plots that
ID: 3311551 • Letter: 5
Question
5. A researcher is investigating the density of earth worms in garden plots that are regularly treated with herbicide and plots that are never treated with herbicide. Twenty soil core samples of 1 liter were taken from each of the untreated and treated soils and the number of earth worms in each core determined. The resulting data are given in the table below. Determine if the density of earth worms is significantly different in these two types of soil Show work and give the p-value. Type of soil Number of carthworms in cach core sample untreated332212 2 1 2433 21123 treatedExplanation / Answer
Group Statistics
Type of soil
N
Mean
Std. Deviation
Std. Error Mean
No. of earthworms
untreated
20
2.05
1.146
.256
treated
20
.65
.813
.182
Independent Samples Test
Levene's Test for Equality of Variances
t-test for Equality of Means
F
Sig.
t
df
Sig. (2-tailed)
Mean Difference
Std. Error Difference
95% Confidence Interval of the Difference
Lower
Upper
No. of earthworms
Equal variances assumed
1.247
.271
4.457
38
.000
1.400
.314
.764
2.036
Equal variances not assumed
4.457
34.255
.000
1.400
.314
.762
2.038
The independent samples t test is performed.
The Levene's test for equality of variances of the two groups indicate that we can assume equality of variances.
The p-value of the t test is statistically significant (less than 0.001)
Thus, we reject the nulll hypothesis that the no. of earthworms in the untreated and treated soil is same.
Hence, we conclude that the no. of earthworms in the treated soil is less than in the untreated soil.
Group Statistics
Type of soil
N
Mean
Std. Deviation
Std. Error Mean
No. of earthworms
untreated
20
2.05
1.146
.256
treated
20
.65
.813
.182
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