Hypothesis Testing
The thing we expect to change when exposed to some other influence
The dependent variable
Based on a normal distribution with a mean of 100 and SD of 10, what percentage of scores fall below 70?
.13%
These two things explain why we can never be 100% certain that a difference between groups is due to the effect of the IV
sampling error, third variables
A researcher conducts a study to assess whether the addition of CCTV cameras in parking lots results in fewer catalytic converter thefts. The independent variable is
CCTV cameras
Compute the z-score for a raw score of 50 where the mean is 50 and the standard deviation is 5
z= 0
This type of error describes a situation where the researcher concludes there is no relationship between variables, when in reality, there is a significant difference between the two variables
Type II error
Research question: Do police officers who pull their firearms more often score differently on measures of empathy compared to officers who pull their firearms less frequently? Provide the most appropriate research hypothesis.
The mean empathy score for officers who pull their firearms more often is significantly different from the mean empathy score for officers who pull firearms less often.
Non-directional
What is the probability of obtaining a score falling at or above 77 where the mean is 75 and the standard deviation is 6?
77-75/6= .33 --> 49.95; 50-49.95= .05
p= 0.0005
A researcher wants to reduce the chance of committing a type I error, how do they do this?
Set the p-value at a lower threshold (i.e., .01)
Using the variables of volunteering and delinquent acts, specify the independent and dependent variables, and provide an appropriate research hypothesis.
IV: volunteering
DV: mean number of delinquent acts
H1: the mean number of delinquent acts committed by juveniles who do not volunteer is significantly greater/different than the mean number of delinquent acts committed by juveniles who do volunteer
Describe the three characteristics of the normal curve
1. mean, median, and mode are equal
2. perfectly symmetrical about the mean
3. tails are asymptotic
A researcher calculates an obtained value of .92 and a critical value of .99. The researcher should conclude what?
That no significant relationship exists
They should retain the null because the OV is less extreme than the CV
Explain what it means to have a sampling error of .83
Our sample is not very representative of the population; therefore, it will be difficult/inappropriate to generalize results to the population. Sampling error this high might indicate that the sample size was too small
Two judges are rated by defendants whose cases were heard by the judges. Higher scores on the measure indicate that judges are viewed more favorably.
Judy got a score of 14.4 on a measure with a mean of 15 and a standard deviation of 3.
Phil got a score of 12.7 on a measure with a mean of 16.2 and a standard deviation of 6.
Which judge is more favored by defendants?
Judy: 14.4-15/3= -0.2
Phil: 12.7- 16.2/6= -.58
Phil is more favored
A researcher found that a sample of death row inmates had a mean IQ score of 94.2 with a standard deviation of 17.9. Calculate the 95% confidence interval and explain what it means.
94.2 +/- 1.96(17.9)
94.2 - 35.08= 59.12
94.2 + 35.08= 129.28
The 95% CI is 59.12- 129.28
This means that the researcher can be 95% confident that the true population mean IQ score for death row inmates lies between 59.12 and 129.28