Researchers are evaluating the longevity of two types of restoration material records from a large dental practice are checked

INSTRUCTIONS TO CANDIDATES

ANSWER ALL QUESTIONS

Homework Assignment #1

Enter the data from questions 1 to 8 in SPSS and perform the appropriate analyses to answer the questions.  Hand in your SPSS output for all the questions with written comments regarding the results.  Use a 5% significance level unless otherwise stated.

1.   Researchers are evaluating the longevity of two types of restoration materials.  Records from a large dental practice are checked and 40 returning patients are found who had a restoration was done with material A more than ten years ago, and 90 are found who had a restoration done with material B.  Records are checked and phone calls are made to find out how many of these restorations have failed in 10 years.  It was found that 8 restorations made from material A and 20 restorations from material B failed within 10 years.  Compute an appropriate hypothesis test to assess whether the proportions of restorations that failed within 10 years differs between the two material types.  Please be sure to explicitly state the null and alternative hypotheses, state a conclusion from the test, and estimate the p-value.  (10 points)

 2.  The following table (on the next page) shows the clinical attachment level of two groups of patients (smokers and non-smokers) at the end of a period of periodontal treatment. We want to know if there is a difference between the groups. Examination of the data using a box and whisker plot (see below) leads us to believe that the data may not be normally distributed. State the appropriate null hypothesis, find the value of the appropriate test statistic and the p-value.  (10 points)

Non-smoker	CAL (mm)		Smoker	CAL (mm)
1	1·0		14	2·8
2	0·6		15	0·0
3	1·1		16	4·2
4	1·2		17	1·3
5	0·7		18	3·6
6	1·3		19	1·6
7	0·9		20	0·9
8	0·4		21	1·3
9	0·9		22	1·0
10	0·2		23	1·5
11	1·4		24	2·8
12	0·9		25	2·8
13	0·8		26	2·0

 3.   Mineral trioxide aggregate (MTAD) is a root canal disinfectant that is a mixture of tetracycline, an acid and a detergent. A study was conducted to compare the antimicrobial activities of MTAD to that of sodium hypochloride (NaOCL). The following data indicate the zone of inhibition (millimeters) on plates inoculated with Enterococcus faecalis (Torabinejad et al., 2002). Suppose that the distribution of the zone of inhibition is normal. Perform a test to detect if there are any significant differences in means between MTAD and NaOCL.  (5 points) 

	Zone of inhibition (mm)
MTAD	35	34	35	35	34	36	35	34
NaOCL	33	34	33	34	36	35	34	36

 4.  (5 points)  An oral health literacy study is looking at the validity of food labels for infants with regards to sugar content.  Eleven cartons of sugar, each nominally containing 1 kg, were randomly selected from a large batch of cartons.  The weights of sugar were:

1.02

1.05

1.08

1.03

1.00

1.06

1.08

1.01

1.04

1.07

1.00.

Do these data support the hypothesis that the mean weight for the batch is 1kg?

5.  Final exam scores in the Biostatistics course for hygiene students, dental students, and residents are given.  Can you conclude that there is a difference in the mean scores of the three groups?  Perform the appropriate parametric and non-parametric statistical tests (made up data).  (10 points) 

	Exam Score
Hygiene	83	88	68	84	74	94	75	80	71
Dental	77	92	48	82	79	85	66	73	82
Residents	98	84	79	88	95	82	76	94	89

 6.  Ten subjects were recruited for a tooth-whitening study.  The subjects were instructed to use Whitestrips once a day for 20 min. per day.  Investigators measured the individual’s L value at the baseline and 7 days to evaluate the effectiveness of the whitening product.  Is there a difference in the mean L value among the two time points?  Perform the appropriate parametric and the non-parametric statistical tests. (5 points)

 

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