Stat 2 MT

A researcher sets up a traffic counter at an intersection. The number of cars that drive over the counter on a given day is what type of variable?

quantitative and discrete

Quantitative vs. Qualitative

Quantitative data is numerical

Qualitative is what you observe with your senses.

Discrete vs. Continuous

Discrete variables can only take set valuables

Continuous variables can take any value in an interval

A demographer uses birth records to keep track of the ages of all the people born in a small town. They keep a log of all the ages in years. This variable is best described as...

quantitative and continuous

For all histograms, the area of a rectangle is __________ the percentage of observations in the corresponding interval.

proportional to

Which way of describing the center is LESS affected by outliers?

the median

Calculate the SD of the following list of numbers and choose the answer that is closest.

1, 2, 4, 5

1.58

Mean

the mean is the average

Median

value at which 50% of the data lie to the right and 50% lie to the left

How to calculate SD

1. Calculate the average

2. Calculate the deviation for each observation (observation-average)

3. Calculate SD using R(square deviations) M(avg squared deviations) S(square root of avg)

A class takes an exam worth 100 points. The average score is 80 points and the SD of the scores is 8 points. A particular student got a 92 on the exam. What was their score in standard units?

1.5

An ecologist measures a group of saplings (young trees) and finds that they have an average circumference of 30 inches, with an SD of 5 inches. A histogram of the circumference values approximately follows the normal curve.

A particular sapling has a 22 inch circumference. What percent of the trees have a circumference that is even smaller than this one's?

You don't need to compute the answer to this problem here, although it would be good practice for you to do so. Instead, just identify: in this problem, you're being asked to convert..

from original units to percentile rank

All observations in a list are multiplied by 5. Which of the following will NOT change?

the observations expressed in standard units

The correlation coefficient r = -0.95 represents a linear relationship that is...

strong and negative

All of the following could be used to enhance a scatterplot by representing variables in addition to those on the x and y axis. Which ones in particular were used in the Hans Rosling video? Check all that apply.

colors representing a qualitative variable

size of symbol representing a continuous quantitative variable

animation to represent time

Due to the regression effect, if an observation is at the 80th percentile of both x and y values, this means the y value is _____________ the average value of y for all the observations at the 80th percentile of x.

larger than

When you see a question that has the following format, how will you fill in the blank?

95% of the regression predictions will be correct to within __________.

2 x RMS error for regression