Psych Stats Exam 2

Before the closure of her gym, Anita was running 5 miles each day on the treadmill to get the exercise she needs to keep fit. At the gym this used to take her about an hour ( µ = 60 minutes). Now, she has a 5 mile route, but she sometimes has to cross the street multiple times to avoid getting too close to others walking along her route. The average variation in her speed due to the varying number of extra steps is about σ = 8 minutes. For a randomly selected morning, what is the probability that Anita's run will take more than 68 minutes? Assume that her run times are normally distributed.

.1587

A normal distribution ha s a mean of µ = 50 with σ = 10. What proportion of the scores in this distribution are greater than X = 55?​

0.3085

What is the standard error given: σ= 10 and n = 25?

2

A population distribution has σ = 5. What position in this distribution is identified by a z-score of z = +1.34?

6.7 points above the mean

If other factors are held constant, how does sample size influence the likelihood of rejecting the null hypothesis and measures of effect size such as Cohen's d?

A larger sample increases the likelihood of rejecting the null hypothesis, but has little influence on the magnitude Cohen's d.

Which of the following accurately describes a hypothesis test?

An inferential technique that uses the data from a sample to draw inferences about a population

True or False: All probabilities can be expressed as decimal values ranging from -1.00 to +1.00.

False

True or False: As the sample size increases, the standard error also increases.

False

True or False: You can reduce the risk of a Type I error by using a larger sample.

False

Is the Mean unusual? M = 25, μ = 20, σ= 5

It depends on the size of the sample

If other factors are held constant, what is the effect of increasing the sample size?

It will decrease the estimated standard error and increase the likelihood of rejecting H0.

Is X an extremely high score? X = 25, μ = 20, σ= -2

It's not possible to have σ= -2

Is the Mean unusual? M = 25, μ = 20, σ= 5, n=25

M is an extremely unusual mean

For a study of the effect on weight of offering unlimited treats to puppies as compared to the weight of puppies given treats only when performing tricks, a researcher randomly assigns 10 puppies to an unlimited treats group, another 10 puppies to a comparison group getting treats only when performing tricks. H1 states:

Puppies with unlimited treats weigh more before the study than puppies who get treats after doing tricks.

Even if a treatment has no effect, it is still possible to obtain an extreme sample mean that is very different from the population mean. What outcome is likely if this happens?

Reject H0 and make a Type I error.

In a typical hypothesis testing situation, H0 and H1, make two different claims about _____

The population after treatment.

True of False: A sample mean with a z score of 2.3 represents an unusual sample mean (M).

True

True or False: A z score of 2.3 represents an unusual raw score (X).

True

True or False: For a hypothesis test using a t statistic, the boundaries for the critical region will change if the sample size is changed.

True

True or False: If a research report includes the term significant result, it means that the null hypothesis was rejected.

True

True or False: If all other factors are held constant, increasing the sample size from n = 25 to n = 100 will increase the power of a statistical test.

True

True or False: If other factors such as sample size, alpha level, and population standard deviation are held constant, the larger the size of the treatment effect, the greater the power of the hypothesis test.

True

True or False: If the sample data are in the critical region with α = .01 in one tail, then the same sample data would still be in the critical region if α were changed to .05 in the same tail.

True

True or False: People are selected to serve on juries by randomly picking names from the list of registered voters. Assume that the average age for registered voters in a particular county is μ = 45 years (σ = 15). A statistician computes the average age for a group of 12 people currently serving on a jury and obtains an average of M=55 years. Assuming that age is normally distributed, it would be extremely unlikely to get a jury with this average age or older in this county.

True

True or False: The distribution of sample means is the collection of sample means for all the possible random samples of a particular size (n) that can be obtained from a population.

True

True or False: There is always a possibility that the decision reached in a hypothesis test is incorrect.

True

Under what circumstances is a score that is located 3 points above the mean an outlier?

When the population standard deviation is less than 1.5

A normal distribution has a mean of µ = 24 with σ = 2. What is the minimum score needed to be in the top 15% of the distribution?​

X = 26.08

Is X an extremely high score? X = 25, μ = 20, σ= 2

X is an extremely high score.

Is X an extremely high score? X = 25, μ = 20, σ= 5

X is not an extreme score

If other factors are held constant, which set of sample characteristics is most likely to produce a significant t statistic?

n= 100 with s2 = 100

Which of the following z-score values represents the location closest to the mean?

z = +0.50

Pediatricians keep height and weight charts for infants and children. If a new study is looking at long term consequences of children in the lowest 8% of height and weight for their age, what is the z score that determines whether a child falls into this category?

​ z = -1.41

If random samples, each with n = 100 scores, are selected from a normal population with µ = 66 and σ = 12, how much difference, on average, should there be between a sample mean and the population mean?​

​1.2 points

Under what circumstances can a very small treatment effect be statistically significant?

​If the sample size is big and the sample variance is small

Which of the following correctly describes the effect of increasing the alpha level (for example, from .01 to .05)?

​Increase the likelihood of rejecting H0 and increase the risk of a Type I error.

Which of the following accurately describes the critical region?

​Outcomes with a very low probability if the null hypothesis is true

A population with µ = 7.8 and σ = 0.55 is transformed into z-scores. After the transformation, what is the standard deviation for the population of z-scores?

​σ = 1.00