Psych stats 3
Once you have the significance value of the t-test, it is beneficial to calculate the effect size. Cohen's d is a measure of effect size. How is it calculated?
(mean 2 - mean 1) / mean of the standard deviation
Suppose we wanted to apply a one-tailed test as opposed to a two-tailed test. How would we covert a significance of p = .284?
.284 / 2 = .142
Participants rated their mood score out of 20 before and after listening to Reign in Blood by the thrash metal band Slayer. What are the degrees of freedom for this study?
7
Assume that for the research into stomach and lung cancer the significance value is set at p < .05 and an independent t-test yielded a significance value of p = .06. What should you do?
Accept the null hypothesis and state that there is no difference in the duration of the survival between the two types of cancer, but that it is worth further investigation.
Which of the following issues are likely to cause Type II error in the cancer survival data?
All of the above
Which of the following statements about the t distribution is correct?
As the degrees of freedom increase, the distribution becomes closer to normal.
How might you classify the measurement scale of the survival rate (days)?
ratio
An independent t-test is used to test for:
Differences between means of groups containing different entities when the sampling distribution is normal, the groups have equal variances and data are at least interval.
An paired-samples t-test is used to test for:
Differences between means of groups containing the same entities when the sampling distribution is normally distributed, and the data have equal variances and are at least interval.
Which of the following t-tests has a different research design?
Independent t-test
A recent study investigated whether vodka is less likely to give you a hangover than wine. Twenty participants on a night out were asked to drink only vodka for the whole evening then rate how they felt the next day out of 10 (0 = I feel fantastic, 10 = I can't move my head in case it explodes). The following month, they were asked to do the same again, only this time they were asked to drink only white wine. The t-score was 2.56. Which of the sentences below is correct? (Hint: You will need to look up the p-value in the table of critical values of the t-distribution in the Appendix.)
It is significant at the 5% level but not the 1% level with a two-tailed test.
Which of the following sentences is an accurate description of the standard error?
It is the standard deviation of the sampling distribution of a statistic.
Participants rated their mood score out of 20 before and after listening to Reign in Blood by the thrash metal band Slayer. What is the null hypothesis of this study?
Listening to Slayer does not affect mood.
A researcher was interested in the effects of emotion-evoking music on exam performance. Before their SPSS exam, a lecturer took one group of students to a room in which calming music was being played. A different group of students were taken to another room in which the 'death march' was being played. The students then did the exam and their marks were noted. The SPSS output is below. The experimenter made no predictions about which form of support would produce the best exam performance. What should he report?
Marks for students receiving positive music before the exam did not significantly differ from students receiving negative music, t(23.12) = 2.05, p = .052.
How is a t-statistic calculated?
Mean difference / standard error of the mean
Which of the following is not a form of t-test?
Mixed model t-test
The degrees of freedom for the paired samples t-test are:
N − 1
Consider an independent t-test. Which of the following expressions best represents the degrees of freedom?
N-2
A researcher measured a group of people's physiological reactions while watching horror films and compared them to when watching comedy films. The resulting data were normally distributed. What test should be used to analyse the data?
Paired-samples (dependent or related) t-test.
Which of the following assumptions are required if a t-test is to be used? (You may select more than one option.)
Samples are drawn from the population at random. correct Samples are drawn from a normally distributed population. correct The data are either interval or ratio. correct Homogeneity of variance.
Which of the following statements best reflects statistical power?
The ability of a statistical test to detect a difference when one genuinely exists
Analyse the heart rate data collected during a VO2 max test. The data points (observations) were collected at the point the lactate threshold occurred (the point at which blood lactate deviates from resting concentrations) before and after a six-week aerobic training programme. When analysing the result of the paired samples t-test, the output presents the following box, but what do the results show you?
The correlation value between the two variables is strong, statistically significant and therefore correct to use.
Analyse the heart rate data collected during a VO2 max test. The data points (observations) were collected at the point the lactate threshold occurred (the point at which blood lactate deviates from resting concentrations) before and after a six-week aerobic training programme. Examine the following SPSS output from the heart rate data. Based on 11 degrees of freedom, working to a two-tailed significance value of .05, the critical value for t is 2.201. What can you assume from the output? (The significance value has been omitted on purpose.)
The data sets were not significantly different.
Run an independent t-test on the data. A Levene's test result of p = .006 was obtained. What does a negative t-statistic suggest?
The lung cancer mean was subtracted from the stomach cancer mean.
What does the independent t-test test assume?
The sampling distribution is normally distributed.
When conducting an independent t-test, what is the dependent variable?
The scores
Run an independent t-test on the data. A Levene's test result of p = .006 was obtained. What can we infer from this number?
The stomach and lung cancer variance is heterogeneous.
Two samples of data are collected and the sample means calculated. If the samples come from the same population, then:
Their means should be roughly equal.
The t-statistic:
Two samples of data are collected and the sample means calculated.
When analysing the cancer survival data, a p-value set at .05 or .01 is most likely to protect against which type of error?
Type I error
How might you classify the measurement scale for the variable labelled as cancer (group)?
nominal
If a significance result of .000 is presented, how should this be reported?
p < .001
