PSYC 245 Exam 2

Explain in your own words the advantages of bigger random samples in a sample survey

A larger sample will give us less variable results; this allows us to receive more

regressive tax

A tax for which the percentage of income paid in taxes decreases as income increases

Standard scores

Observations expressed in standard deviations above or below the mean of a distribution

Difference between parameter and statistic?

The parameter will be based on all data collected while the statistic is based on the sample

Why take the square root of the equation when calculating std. deviation?

1. Because we squared all the deviances 2.Leaving it in the squared form gives us the variance, we're trying to make it simplified 3. brings us back to the original scale of the variable

How to find the median

1. If the number of observations n is odd, the median M is the observation that lies in the center of the ordered list. Find the location of the median by counting (n+1)/2 observations up from the bottom of the list. 2. If the number of observations n is even, the median M is the average of the two center observations in the ordered list. The location of the median is again (n+1)/2 from the bottom of the list.

When describing distributions of quantitative variables,

1. take note of significant deviations from the rest of the data 2. be able to distinguish skews from symmetric distributions as well as # of major peaks 3. include numerical measures regarding the shape

You plan to take a sample of size 500 to estimate the proportion of students at your school who support having no classes and special presentations on Veteran's Day. To be twice as accurate with your results, you should plan to sample how many students?

2000 students

the quartiles are the

25% and 75% percentiles

median of any distribution is the

50% percentile

The Ministry of Health in the Canadian province of Ontario wants to know whether the national health care system is achieving its goals in the province. Much information about health care comes from patient records, but that source doesn't allow us to compare people who use health services with those who don't. So the Ministry of Health conducted the Ontario Health Survey, which interviewed a random sample of 61,239 people who live in the province of Ontario. WHAT IS THE POPULATION? WHAT IS THE SAMPLE?

Population, Ontario residents. Sample, 61,239 residents interviewed.

Why divide by N-1 in the std. deviation formula? (Bessel's Correction)

Small sample sizes tend to underestimate population SD if you divide by N; subtracting 1 will make give smaller sample sizes a larger, clearer effect

standard deviation

measures the average distance of the observations from their mean. It is calculated by finding an average of the squared distances and then taking the square root.

You should make a bar graph of a distribution to display

a categorical variable, or in general to compare related quantities

parameter

a set of fixed limits that control the way that something should be done

mean

a set of observations is their arithmetic average.

A November 2017 Gallup Poll of 1028 U.S. adults found that 627 are satisfied with the total cost they pay for their health care. The announced margin of error is percentage points. The announced confidence level is 95%. a. What is the value of the sample proportion who say they are satisfied with the total cost they pay for their health care? b. Make a confidence statement about the parameter .

a. The value of the statistic is 61% b. We are 95% certain that the amount of people surveyed that are satisfied with their healthcare is between 57%-65%.

Which statement(s) are true about std. deviation? a. SD ≥ 0, always b. SD = 0 only when all observations are identical and increases as the spread increases c. SD has the same units as the original measurements d. SD is greatly increased by outliers or skewness e. All of the above

e. All of the above

the median is more or less affected by extreme values than the mean?

less affected.

When making a stem plot, how do you adjust the data to make it effective?

round data as needed.

Formula for standard score

standard score=observation−mean/standarddeviation

Data analysis is

the art of describing data using graphs and numerical summaries

What is the preferred method of expressing the measure and spread of skewed distributions?

the five-number summary

What is the preferred method of expressing the measure and spread of symmetric distributions?

the mean and std. deviation

1st quartile

the median of the observations whose position in the ordered list is to the left of the location of the overall median. The overall median is not included in the observations considered to be to the left of the overall median; 25%

3rd quartile

the median of the observations whose position in the ordered list is to the right of the location of the overall median. The overall median is not included in the observations considered to be to the right of the overall median.

skewness in a distribution moves the mean away from

the median toward the long tail

Median

the midpoint, the value that separates the smaller half of the observations from the larger half. The middle 50% of the observations fall between the first and third quartiles.

Five-number summary

the most extreme values in the data set (the maximum and minimum values), the lower and upper quartiles, and the median

regression line

the relationship between an explanatory and a response variable

Why square the differences instead of taking the absolute values of the deviances?

the squared values are more sensitive to outliers