Opinions about whether caffeine enhances test performance differ. You design a study to test the impact of drinks with different caffeine contents on students’ test-taking abilities. You choose 21 students at random from your introductory psychology course to participate in your study. You randomly assign each student to one of three drinks, each with a different caffeine concentration, such that there are seven students assigned to each drink. You then give each of them a plain capsule containing the precise quantity of caffeine that would be consumed in their designated drink and have them take an arithmetic test 15 minutes later. The students receive the following arithmetic test scores:   Water Coffee Espresso   Caffeine Content (mg/oz) 0 13.4 51.3     78 92 83 ΣX² = 142,493   88 87 83 G = 1,723   72 80 76 N = 21   72 89 79 k = 3   64 96 86     81 83 79     82 92 81     T₁ = 537 T₂ = 619 T₃ = 567     SS₁ = 381.43 SS₂ = 185.71 SS₃ = 66     n₁ = 7 n₂ = 7 n₃ = 7     M₁ = 76.7143 M₂ = 88.4286 M₃ = 81.0000     You plan to use an ANOVA to test the impact of drinks with different caffeine contents on students’ test-taking abilities. What is the null hypothesis? The population mean test scores for all three treatments are equal.   The population mean test scores for all three treatments are not all equal.   The population mean test score for the water population is different from the population mean test score for the coffee population.   The population mean test scores for all three treatments are different.     Calculate the degrees of freedom and the variances for the following ANOVA table: Source SS df MS Between                Within 633.14           Total 1,124.95          The formula for the F-ratio is: FF  =  =  MSbetweenMSbetween  /  /  MSwithinMSwithin   Using words (chosen from the dropdown menu), the formula for the F-ratio can be written as: FF  =  =        /  /         Using the data from the ANOVA table given, the F-ratio can be written as: FF  =  =        /  /         Thus: FF  =  =         Use the Distributions tool to find the critical region for α = 0.01.   F Distribution Numerator Degrees of Freedom = 26 Denominator Degrees of Freedom = 26             012345678F   At the α = 0.01 level of significance, what is your conclusion?   You cannot reject the null hypothesis; caffeine does appear to affect test performance.   You cannot reject the null hypothesis; you do not have enough evidence to say that caffeine affects test performance.   You can reject the null hypothesis; caffeine does appear to affect test performance.   You can reject the null hypothesis; you do not have enough evidence to say that caffeine affects test performance.

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7. Hypothesis testing with ANOVA

Opinions about whether caffeine enhances test performance differ. You design a study to test the impact of drinks with different caffeine contents on students’ test-taking abilities. You choose 21 students at random from your introductory psychology course to participate in your study. You randomly assign each student to one of three drinks, each with a different caffeine concentration, such that there are seven students assigned to each drink. You then give each of them a plain capsule containing the precise quantity of caffeine that would be consumed in their designated drink and have them take an arithmetic test 15 minutes later.
The students receive the following arithmetic test scores:
 
Water
Coffee
Espresso
 
Caffeine Content (mg/oz) 0 13.4 51.3  
  78 92 83 ΣX² = 142,493
  88 87 83 G = 1,723
  72 80 76 N = 21
  72 89 79 k = 3
  64 96 86  
  81 83 79  
  82 92 81  
  T₁ = 537 T₂ = 619 T₃ = 567  
  SS₁ = 381.43 SS₂ = 185.71 SS₃ = 66  
  n₁ = 7 n₂ = 7 n₃ = 7  
  M₁ = 76.7143 M₂ = 88.4286 M₃ = 81.0000  
 
You plan to use an ANOVA to test the impact of drinks with different caffeine contents on students’ test-taking abilities. What is the null hypothesis?
The population mean test scores for all three treatments are equal.
 
The population mean test scores for all three treatments are not all equal.
 
The population mean test score for the water population is different from the population mean test score for the coffee population.
 
The population mean test scores for all three treatments are different.
 
 
Calculate the degrees of freedom and the variances for the following ANOVA table:
Source
SS
df
MS
Between               
Within 633.14          
Total 1,124.95       
 
The formula for the F-ratio is:
FF  =  =  MSbetweenMSbetween  /  /  MSwithinMSwithin
 
Using words (chosen from the dropdown menu), the formula for the F-ratio can be written as:
FF  =  =        /  /      
 
Using the data from the ANOVA table given, the F-ratio can be written as:
FF  =  =        /  /      
 
Thus:
FF  =  =      
 
Use the Distributions tool to find the critical region for α = 0.01.
 

F Distribution

Numerator Degrees of Freedom = 26

Denominator Degrees of Freedom = 26

     
     
012345678F
 
At the α = 0.01 level of significance, what is your conclusion?
 
You cannot reject the null hypothesis; caffeine does appear to affect test performance.
 
You cannot reject the null hypothesis; you do not have enough evidence to say that caffeine affects test performance.
 
You can reject the null hypothesis; caffeine does appear to affect test performance.
 
You can reject the null hypothesis; you do not have enough evidence to say that caffeine affects test performance.
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