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Research Methods Topics 47-52
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Terms in this set (56)
When researchers study a sample, are the results called the "true results" or the "observed results"?
observed results (true results are obtained is a researcher questions the entire population)
What is the name of the test of the null hypothesis used in this topic?
Chi-square test
According to this topic, should the typical consumer try to interpret the value of df?
No. Degrees of freedom (df) should be thought of as substeps in the mathematical procedure for obtaining the value of p.
What is the symbol for probability?
p
If a researcher found that a chi-square test of a difference yielded a p of less than 5 in 100 (p<.05), on the basis of conventional wisdom, what should the researcher conclude about the null hypothesis?
Reject the null hypothesis. The difference observed was probably not created by random sampling errors.
Does "p <.05" or "p >.05" usually lead a researcher to declare a difference statistically significant?
p <.05
If a researcher fails to reject a null hypothesis, is the difference in question statistically significant?
No. The probability that sampling error created the difference is too great for it to be rejected as a possible explanation
If a researcher has a statistically significant result, should the null hypothesis remain on the list of viable explanation for an observed difference?
No
The values of chi-square and degrees of freedom (df)-
calculated solely to obtain the probability that the null hypothesis is correct. They are not descriptive statistics that a typical consumer of research should attempt to interpret.
Null hypothesis
- asserts that any observed difference was created by random sampling errors (i.e., in the population, the true difference is zero). Put another way, the null hypothesis states the observed differences is an illusion created by random errors created by random sampling (sampling errors).
Which type of analysis classifies participants in terms of two variables in order to examine the relationship between the two variables?
Bivariate analysis
What decision should researchers make about the null hypothesis if a chi-square test leads to the conclusion that the observed differences are unlikely to be due to random errors?
Reject their null hypothesis. Note that a researcher can never be certain that he/she has made the correct decision when rejecting a null hypothesis. (Type I Error)
If p= .05 for a chi-square test, chances are how many in 100 that the null hypothesis is true?
There are 5 in 100 chances that the null hypothesis is correct
When a researcher uses the .01 level, what are the odds of making a Type I Error?
1 in 100
What is the name of the error researchers make when they fail to reject the null hypothesis when, in fact, it is an correct hypothesis?
• Type II Error
What is the name of an error researchers make when they reject the null hypothesis when, in fact, it is a correct hypothesis?
Type I Error
Why is random sampling desirable even though it creates errors?
• Because random sampling is free from bias
According to Figure 1, about how many participants had a score of 16?
• 55
In figure 1, are the frequencies on the "vertical" or the "horizontal" axis?
• Vertical axis
What is the name of the curve that is symmetrical (smooth, bell-shaped)?
• Normal curve
If a distribution has some extreme scores on the right (but not on the left), it is said to have what type of skew?
• Negative skew (skewed to the left)
If a distribution is skewed to the left, does it have a "positive" or a "negative" skew?
• negative
In most populations, income has what type of skew?
• Positive (Most individuals earn relatively small amounts, so the curve is high on the left
Does a distribution with a tail to the right have a "positive" or a "negative" skew?
• Positive skew (the tail is to the right)
Frequency polygon
an easy to read graph that shows quantitative data as frequency distribution. Frequency is on the vertical y-axis, and the measured scores are on the horizontal x-axis
Skewed
when distributions have a tail on one side on not the other
Positive skew
a distribution that is skewed to the right (the tail is to the right)
Negative skew
a distribution that is skewed to the left (the tail is to the left)
Which average is defined as the most frequently occurring score?
• mode
Which average is defined as the balance point in a distribution?
• mean
Which average is defined as the middle score?
• median
What is the formal definition of the mean?
• The balance point in a distribution
How is the mean calculated?
• Add up the scores and then divide by the number of scores
Should the mean be used for highly skewed distributions?
• No, use the median as an average
Should the median be used for highly skewed distributions?
• Yes
Which one of the three averages is very seldom used in formal reports of research?
• The mode
What is a synonym for the term average?
• Measures of central tendency
Which average is usually reported when the standard deviation is reported?
• The mean
What is meant by the term variability?
• The amount by which participants vary or differ from each other
Is it possible for two groups to have the same mean but different standard deviation?
• yes
If all individuals in a group have the same score, what is the value of the standard deviation for the scores?
• SD= 0, there is no variability
What percentage of the participants lies within one standard-deviation unit of the mean (i.e., on both sides of the mean) in a normal distribution?
• If a distribution is normal, 68% of the participants in the distribution lie within one standard-deviation unit of the mean.
The middle 60% of the participants in a normal distribution have scores between what two values if the mean equals 100 and the standard deviation equals 15?
• Between 85 and 115 (100-15= 85 and 100+15=115)
If the mean of a normal distribution equals 50 and the standard deviation equals 5, what percentage of the participants have scores between 45 and 50?
• 68%
8. Does the 68% rule apply if a distribution is not normal?
• No. The less normal the distribution is, the less accurate the 68% rule is.
If the standard deviation for Group X is 14.55 and the standard deviation for Group Y is 20.99, which group has less variability in its scores?
• Group X has less variability
. Refer to question 9. Does "Group X" or "Group Y" have a narrower curve?
• Narrower curve than Group Y. The smaller the standard deviation, the narrower the curve.
If the median for a group of participants is 25.00, what percentage of the participants has scores above a score of 25.00?
• 50%
Should the "mean" or the "median" be used with ordinal (data that put participants in order from high to low but do not have equal intervals among them) data?
• Median
How is the range of a set of scores calculated?
• The highest score minus the lowest score
. Is the "range" or the "interquartile range" a more reliable statistic?
• Interquartile range, because the range is based on the two most extreme scores, it is an unreliable statistic.
The interquartile range is the range of what?
• Range of the middle two quarters
Suppose a researcher reported that for Group X, the median equals 55.1 and the IQR equals 30.0, while for Group Y, the median equals 62.9 and the IQR equals 25.0. Which group has the higher average score?
• Group Y, it's median is 62.9 vs. 55.1
On the basis of the information in question 6, the scores for which group are more variable?
• Group X, it's IQR is 30 vs. 25. The larger interquartile range for Group X indicates greater variability.
Which statistics discussed in this topic are measures of variability?
• Range and inter-quartile range
When the median is reported as the measure of central tendency, it is customary to report which measure of variability?
• Interquartile range
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