Grace Mayne

Clinical Data Management

July 4th 2016

Polit dataset C

B1.

Case Processing Summary
Cases
Valid / Missing / Total
N / Percent / N / Percent / N / Percent
CES-D Score / 962 / 96.2% / 38 / 3.8% / 1000 / 100.0%
Descriptives
Statistic / Std. Error
CES-D Score / Mean / 18.5831 / .37821
95% Confidence Interval for Mean / Lower Bound / 17.8409
Upper Bound / 19.3253
5% Trimmed Mean / 18.0339
Median / 17.0000
Variance / 137.609
Std. Deviation / 11.73067
Minimum / .00
Maximum / 57.00
Range / 57.00
Interquartile Range / 17.00
Skewness / .644 / .079
Kurtosis / -.164 / .158
Tests of Normality
Kolmogorov-Smirnova / Shapiro-Wilk
Statistic / df / Sig. / Statistic / df / Sig.
CES-D Score / .072 / 962 / .000 / .959 / 962 / .000
a. Lilliefors Significance Correction

a)What is the range for the CES-D scores in this sample of low income women?

Range is 57.0.

b)What are the mean, SD and SEM for the CES-D scores?

Mean is 18.5831, SD is 11.73067and the SEM is .37821.

  1. What is the 95% CI? What does this mean?
  2. The CI estimates that the value of the standard curve lies within 2 standard deviations of the mean (in general CI can be for unknown parameter, don’t have to be mean always, for example CI of variance). The alpha value in this sample would be .05. IT can be interpreted as there is a 95% probability that the means would fall with 2 standard deviations.
  1. What is the value of the test statistics and significance level for the Kolmogorov-Smirnov test? What does it mean?

Kolmogorov-Smirnov is normally used with a small sample size and tests for normal distribution of outcomes (in general it test if population has distribution F, but in this case it is Normal distribution). The statistics value is .072 and the significance level is .000 which is indicative of a p value less than .001 making it statistically significant.

  1. Do you think the CES-D scores dataset can be used in the dependent variable in t tests?

The CES-D dataset could be used if they were considered as dependent are from the same sample but are paired i.e. boys in one group and girls in the other group.

It can be used if we are measure two characteristics of same person. In case we have information for CES-D of 962 women, as in our case, if we separate this sample in two groups it would be independent.

B2 In a study sample of 962 women by suing sample distribution and the laws of probability to accept or reject the null hypothesis. In this sample the CES-D scores will be statistically tested to see if there are or no differences between the scores of the two group of women

.

a)( H0)There are no differences in the CES-D scores of for the women working and the women not working.

(H1) There are differences in the CES-D scores of the women working and the women not working.

b) Would an independent or dependent t test be appropriate? Why?

Independent t test would be appropriate as this two groups of women are independent.

c) Did you state a directional or non-directional hypothesis?

A directional hypothesis states that the null hypothesis is incorrect.

Non-directional hypothesis were stated above, A nondirectional alternative hypothesis states that the null hypothesis is wrong. A nondirectional alternative hypothesis does not predict whether the parameter of interest is larger or smaller than the reference value specified in the null hypothesis.

c)What does this imply about a one-tailed versus a two-tailed?

c)

d)A one-tailed test is used if there is an assumption beforehand that the directional hypothesis and that there is a significant difference which can either be large or small[J1].

e)A two-tailed test the significance can also be large or small [J2]but it is non-directional. is used when we have non-directional alternative hypothesis.

T-Test

Group Statistics
Currently employed? / N / Mean / Std. Deviation / Std. Error Mean
CES-D Score / No / 524 / 20.8965 / 12.46425 / .54450
Yes / 436 / 15.8239 / 10.13655 / .48545

B3.

a) How many women were employed versus unemployed?

There were 436 who were employed and 524 women who were not employed.

b)What were the mean CES-d scores for the employed and non-employed women

The mean CES-D score for the employed women is 15.8239 and 20.8965 for the women not employed.

c)What is the value of the F statistic for Levene’s test and what is the level of significance? What does this mean?

The F value for Levene’s test is 23.615. Levene’s tests for equal variances. Level of significance is .000 so we can conclude that we reject null hypothesis, these two groups has not the same variances.

d)What formula for t test is appropriate in this situation- the pooled variance or separate variance formula? Why?

This sample used t-test for pooled variance because the sample sizes were identical.[J3]

If the sample variances are not very different, one can use the pooled 2-sample t-interval. As we have concluded above that variances were different, we should use separate variance formula.

e)What is the value of t for the appropriate test? What is the level of significance and what does this mean?

The value of t is 6.825 and it is appropriate. The significance level is .000 that means that the p value is less than .05. It means that there is a significant difference between means of the two groups.

f)If you had used the other formula, would you have arrived at a differentconclusion?

If the other formula was used the conclusion would have been different and incorrect.

For some examples, one can use both the pooled t-procedure and the separate variances (non-pooled) t-procedure with the results close to each other. However, when the sample standard deviations are very different from each other and the sample sizes are different, the separate variances 2-sample t-procedure is more reliable.

g)A confidence interval indicates that there is a 95% probability that the true population value lies somewhere between the lower and upper confidence limits.

[J1]I am not sure what do you want to say by this part of sentence,

[J2]I am not sure what do you want to say by this part of sentence,

[J3]How identical as we have 524 and 436?