PSYC 311 exam 2
Which of the following statements is true about normal distributions?
Around 2/3 of scores located within 1 standard deviation of the mean.
As the sample size is increased, the distribution of t statistics becomes flatter and more spread out.
False
Assignment bias is a threat to external validity.
False
For a population with mean = 80 and standard deviation = 10, what is the z-score corresponding to X = 95?
+ 1.50
For a population with mean of 80 and variance of 36, what is the z-score corresponding to X = 68?
-2.00
A sample of n = 20 scores is transformed into z-scores. What is the mean for the set of 20 z-scores?
0
For any distribution, what is the z-score corresponding to the mean?
0
If an entire sample with M = 60 and s = 8 is transformed into z-scores, then the distribution of z-scores will have a mean of ___ and a standard deviation of ___.
0 and 1
A sample of n = 4 scores has SS = 48. What is the estimated standard error for the sample mean?
2
For a sample with M = 80, a score of X = 88 corresponds to z = 2.00. What is the sample standard deviation?
4
For a sample with M = 50 and s = 12, what is the X-value corresponding to z = -0.25?
47
For a sample with M = 40 and s = 8, what is the X-value corresponding to z = 1.50?
52
For a sample with M = 80 and s = 10, what is the X-value corresponding to z = -0.50?
75
Which set of characteristics will produce the smallest value for the estimated standard error?
A large sample size and a small sample variance
What is true about testing relations between 2 variables using chi-square?
Both variables are either categorical, nominal, or qualitative.
A researcher is conducting a study in which a treatment group is compared to a no-treatment control group. The treatment group is tested in the lab and the control group is tested in a classroom. Time is likely to be a threat to the internal validity of the study.
False
For a sample with M = 30, a score of X = 24 corresponds to z = -2.00. The standard deviation for the sample is s = 6.
False
For a sample with a standard deviation of s = 8, a score of X = 42 corresponds to z = -0.25. The mean for the sample is M = 40.
False
If two samples each have the same mean, the same number of scores, and are selected from the same population, then they will also have identical t statistics.
False
If two samples are selected from the same population, under what circumstances will the two samples have exactly the same one-sample t statistic?
If the samples are the same size and have the same mean and have the same variance.
How does sample variance influence the likelihood of rejecting the null hypothesis and measures of effect size such as Cohen's d?
Larger variance decreases both the likelihood and measures of effect size.
A sample with M = 85 and s = 12 is transformed into z-scores. After the transformation, what are the values for the mean and standard deviation for the sample of z-scores?
M = 0 and s = 1
In a sample with s = 8, a score of X = 44 corresponds to a z-score of z = -0.50. What is the sample mean?
M = 48
You have a score of X = 65 on an exam. Which set of parameters would give you the best grade on the exam?
M = 60 and s = 5
For a sample with s = 12, a score of X = 73 corresponds to z = +1.00. What is the sample mean?
M = 61
In a sample of scores, X = 83 corresponds to z = -0.50 and X = 93 corresponds to z = +2.00. What are the values for the sample mean and standard deviation?
M = 85 and s = 4
For an exam with a mean of M = 74 and a standard deviation of s = 8, Mary has a score of X = 80, Bob's score corresponds to z = +1.50, and Sue's score is located above the mean by 10 points. If the students are placed in order from smallest score to largest score, what is the correct order?
Mary, Sue, Bob
A researcher designs a study to determine whether female preschoolers prefer sweetened or unsweetened cereal. The researcher first presents the children with the sweet cereal and measures how much they ate. Later, during the same session, the researcher presents the children with the unsweetened cereal and measures how much they ate. The research finds that the group of preschoolers ate more of the sweetened cereal and therefore prefers the sweetened cereal. Is this conclusion justified?
No; this conclusion is not justified. Time-related variables could threaten the results.
Skew
Positive: mean < median < mode Negative: mean > median > mode
Skew tail directions
Positive: tail points right Negative: tail points left
Last week Sarah had exams in Math and in Spanish. On the Math exam, the mean was M = 40 with s = 5 and Sarah had a score of X = 45. On the Spanish exam, the mean was M = 60 with s = 8 and Sarah had a score of X = 68. For which class should Sara expect the better grade?
The grades should be the same because the two exam scores are in the same location.
A teacher gave a reading test to a class of 5th graders and computed the mean, median, and mode. What can't be true?
The majority of the students had scores above the median.
Two samples from the same population both have n = 10 scores with M = 45. If the t statistic is computed for each sample, then what is the relationship between the two t values?
The sample with the smaller variance will produce the larger t statistic
If a researcher is using an independent-groups t statistic to test a null hypothesis about a population, what information is needed from the population to calculate the t statistic?
The t statistic does not require any information about the population.
Which of the following is a fundamental difference between the t statistic and a z-score?
The t statistic uses the sample variance in place of the population variance.
A score with a value less than or equal to the mean will have a z-score that is less than or equal to zero.
True
Although hypothesis tests are affected by sample size, it has little or no influence on measures of effect size, such as Cohen's d.
True
As sample size increases, the critical region boundaries for a two-tailed test with α = .05 will move closer to zero.
True
Experimenter bias and participant reactivity can threaten both internal and external validity.
True
For a hypothesis test using a t statistic, the boundaries for the critical region will change if the sample size is changed.
True
For a population with a standard deviation of 12, a z-score of z = +0.50 corresponds to a score that is above the mean by 6 points.
True
For a sample with a mean of M = 50 and a standard deviation of s = 10, a z-score of z = +2.00 corresponds to X = 70.
True
For a sample with a mean of M = 76, a score of X = 72 corresponds to z = -0.50. The sample standard deviation is s = 8
True
If the participants in one treatment condition are noticeably older than the participants in another treatment condition, then participant age is a confounding variable.
True
If two samples, each with n = 20 scores, are selected from the same population and both have the same mean (53) and the same variance (12), then they will also have the same one-sample t statistic.
True
On an exam, Tom scored 12 points above the mean and had a z-score of +2.00. The standard deviation for the set of exam scores must be 6.
True
Selection bias is a threat to external validity.
True
Simulation and field studies are used to increase the external validity of experiments.
True
Simulation involves bringing aspects of the real world into the laboratory.
True
The mode is the best way to measure central tendency for data from a nominal scale of measurement.
True
The problem with using college students as research participants is that college students are not perfectly representative of the general adult population.
True
The results of a study may be limited to the way the variable is measured.
True
The t distribution for df = 4 is flatter and more spread out than the t distribution for df = 20.
True
Two samples from the same population probably will have different t statistics even if they are the same size and have the same mean.
True
What does UTOS stand for?
Units: people, groups, elements of sample Treatment: dosage levels, manipulations Observations: operational definitions, measures Settings: where study took place (Ex: lab, field, survey, online)
A distribution with M = 35 and s = 8 is being standardized so that the new mean and standard deviation will be M = 50 and s = 10. In the new, standardized distribution your score is X = 45. What was your score in the original distribution?
X = 31
A distribution with M = 55 and s = 6 is being standardized so that the new mean and standard deviation will be M = 50 and s = 10. When the distribution is standardized, what value will be obtained for a score of X = 58 from the original distribution?
X = 55
A sample has M = 72 and s = 4. In this sample, what is the X-value corresponding to z = -2.00?
X = 64
The ages of the children in a summer camp range from 7 to 12 years old. A counselor constructs a frequency distribution graph showing the number of children for each of the six age groups. Which of the following graph would be most appropriate for this distribution?
a histogram
In which research situation would the study be described as confounded?
an extraneous variable varies systematically along with the two variables being studied
In research studies that compare different groups of individuals for each of the treatment conditions, ____ is a threat to internal validity.
assignment bias
Demand characteristics can threaten internal validity because the results ____.
can be explained by reactivity instead of the treatment conditions
A study examining the relation between humor and memory compares memory performance scores for one group presented with humorous sentences and a second group presented w/ nonhumorous sentences. The participants presented with the humorous sentences are all males. The participants presented with the nonhumorous sentences are all females. In this study, gender is best characterized as a(n) ____ variable.
confounding
A sample is selected from a population with a mean of 46 and a treatment is administered to the sample. After treatment, the sample mean is M = 48 with a sample VARIANCE of 16. Based on this information, the size of the treatment effect, as measured by Cohen's d, is ____.
d = 0.50
What is experimental realism?
degree to which an experiment absorbs (psychologically) and involves its participants
Statistical techniques that summarize, organize, and simplify data are best classified as ____ statistics.
descriptive
The results of a study may be influenced by the experimenter's expectations regarding the outcome of the study. This artifact is known as ____.
experimenter bias
A researcher is concerned that experimental results obtained with college students may not apply to adults in the general population. This illustrates a concern with ____ validity.
external
A researcher finds that a particular medication causes rats' memory to improve. A second researcher plans to test this medication with humans diagnosed with Alzheimer's disease. The second researcher is addressing the problem of ____.
external validity
A researcher finds that in a laboratory a meditation session decreases anxiety scores of college students. The researcher wonders whether the meditation session would decrease anxiety in clients diagnosed with an anxiety disorder. This researcher is considering the ____ of the findings.
external validity
A study examining the relation between humor and memory compares memory performance scores for one group presented with humorous sentences and a second group presented w/ nonhumorous sentences. The participants in both groups consist of a mixture of males and females. In this study, gender is best characterized as a(n) ____ variable.
extraneous
A(n) ____variable is a variable in a study that is not being directly studied.
extraneous
What is a type II error?
failing to reject a false null hypothesis
To construct a frequency distribution graph displaying a set of scores that were measured on an interval or a ratio scale, you should use a ____.
histogram
What is the advantage of a simulation compared to a traditional laboratory study?
increased external validity
Increasing sample size _______ the value of the test statistic?
increases
Sensitization can threaten external validity because the results obtained in a study may be limited to ____.
individuals who have experienced a pretest
A researcher studies a group of 25 preschool children in order to answer questions about the entire population of preschool children. What general categories of statistical techniques will this researcher be using?
inferential statistics
A research study finds that a group of participants who received relaxation training had lower exam anxiety scores than a group who did not receive training. However, the researcher suspects that the difference between groups may be caused by the fact that the participants in one group are generally smarter than those in the other. This study has a problem with ____.
internal validity
When participants in one treatment condition have characteristics that are different from the characteristics of participants in another treatment condition, then ____ may be threatened.
internal validity
Researchers often use simulation experiments in an attempt to obtain the ____ of an experiment and still keep much of the ____ of research conducted in the real world.
internal validity; external validity
When research is conducted in a ____, researchers should always be concerned that participants' behaviors may be influenced by ____.
laboratory; reactivity
Although field studies tend to have higher external validity that traditional laboratory studies, they also tend to have ____.
lower internal validity
For scores measured on a nominal scale of measurement (for example, job classification), which measure of central tendency is appropriate?
mode
A researcher conducts a one-sample t-test using a sample from an unknown population. If the t statistic has df = 35, how many individuals were in the sample?
n = 36
A sample of n = 16 scores produces a one-sample t-statistic = 2. 00. If the sample is used to measure effect size with r2, what value will be obtained for r2?
r2 = 4/19
Selecting a smaller alpha level ________ the risk of ________.
reduces; Type I error
A sample with M = 85 and s = 12 is transformed into z-scores. After the transformation, what is the standard deviation for the sample of z-scores?
s = 1.00
On an exam with M = 52, you have a score of X = 44. Which value for the standard deviation would give you the highest position in the class distribution relative to the rest of the students?
s = 8
A researcher moves the real world into the laboratory. This type of research is called a ____.
simulation study
Where is a score of X = 45 located in a distribution with a mean of 40 and a standard deviation of 12?
slightly above average
A characteristic, usually a numerical value that describes a sample, is called a ____.
statistic
A researcher designs a study to determine whether teaching style affects third grader's motivation to succeed in math. One teacher, with one style, teaches math to one class of children. Another teacher, with a different style, teaches math to a different class of children. The researcher finds that the children in the first class are more motivated to succeed in math. These differences in motivation can be explained by ____.
teaching styles and teachers
What is the definition of variance?
the average squared distance from the mean
What is mundane realism?
the extent to which the research setting resembles the real-world setting of interest
If a distribution of numerical scores contains one or two extremely high values, compared to the rest of the scores, which measure of central tendency would produce the most representative value?
the median
A sample has s = 6. What position in this distribution is identified by a z-score of z = +2.00?
twelve points above the mean
Under what circumstances is a score that is located 5 points above the mean a central value, relatively close to the mean?
when the population standard deviation is much greater than 5
Under what circumstances is a score that is 15 points above the mean an extreme score relatively far from the mean?
when the population standard deviation is much smaller than 15
