In: Statistics and Probability
Smoking increases the risk of developing more than 50 serious
health conditions. Some may be fatal, and others can cause
irreversible long-term health damage.
It is hypothesized that smoking may cause wrinkles around eyes. The
smoking behaviour and the information about wrinkles around eyes
are recorded and the following frequency table is obtained.
Heavy wrinkles Moderate wrinkles No wrinkles
Heavy smoker 95 5 50
Light or nonsmoker 103 7 240
Do these data show association between smoking and wrinkles around
eyes? Formulate a suitable statistical model and a statistical
hypothesis test to analyse these data, and state your
conclusion
ANSWER::
Ho: given two variable are independent
H1: Given two variables are not independent
...........
Chi-Square Test of independence | |||||||
Observed Frequencies | |||||||
heavy wrinkle | moderate wrinkle | no wrinkle | Total | ||||
heavy smoker | 95 | 5 | 54 | 154 | |||
light smoker | 103 | 7 | 240 | 350 | |||
Total | 198 | 12 | 294 | 504 |
Expected frequency of a cell = sum of row*sum of column / total sum | |||||||
Expected Frequencies | |||||||
heavy wrinkle | moderate wrinkle | no wrinkle | Total | ||||
heavy smoker | 198*154/504=60.5 | 12*154/504=3.667 | 294*154/504=89.833 | 154 | |||
light smoker | 198*350/504=137.5 | 12*350/504=8.333 | 294*350/504=204.167 | 350 | |||
Total | 198 | 12 | 294 | 504 |
(fo-fe)^2/fe | heavy wrinkle | moderate wrinkle | no wrinkle |
heavy smoker | 19.674 | 0.485 | 14.293 |
light smoker | 8.656 | 0.213 | 6.289 |
................
Chi-Square Test Statistic,χ² = Σ(fo-fe)^2/fe
= 49.6107
Level of Significance = 0.05
Number of Rows = 2
Number of Columns = 3
Degrees of Freedom=(#row - 1)(#column -1) = (2- 1 ) * ( 3- 1 )
= 2
p-Value = 0.0000
Decision: p-value < α , Reject Ho
...............
so, there is association between smoking and wrinkle around eyes.
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