Unit Quiz 2 Flashcards
Rules for density curve
Area under the curve is one
always on or above the X axis is horizontal
it is the overall pattern of distribution
Facts about normal distributions
bell shaped
Roughly symmetric
Unimodal
Npp will be linear
If the distribution has a constant added or subtracted to it what is the effect on the distribution
The center changes by the constant is added or subtracted by the constant
there is no effects to the shape
there is no effects to the spread
If the distribution is multiplied or divided by constant what happens to the distribution
The center is multiplied or divided by the constant there’s no effect to the shape
the spread is multiplied or divided by that constant
Mean is greater than median
Right skewed
mean less than median
Left skewed
Right skewed
Mean is greater than median
Left skewed
Mean is less than median
Percentages for normal distribution
68, 95, 99.7 … 100
Formula to find a score
Number of observations minus mean all over standard deviation
Finding area to the left(less than the value)
Table A of that value
Finding area to the right(more than the value)
1- table A of that value
Area between(between 2 values)
Bigger table A(value more to the right) minus smaller table A(value more to the left)
Given area find Z
Look I’m center of table A and look outwards to column and rows to identify z score
What does proportions means
U should standardize(use z score)
when do you use z score vs percentages
Z score when comparing, or proportions or even possibly finding the percentage
the path percentile of a distribution is the value with
p percent of observations less than it
What is a cumulative relative frequency graph used for
It is used to determine the position of an individual within a distribution or to locate a specified percentile of the distribution
What value should the fuck you want to frequency be? (percent wise)
1 or 100%
How is the z score interpreted in analysis or questions when u have to explain (for ex,pale the z -score is -0.51)
This observation was .59 SDU(standard deviation units) below the mean
Can u subtract z scores then find the area?
NO always use stable A first then subtract!
Remember z scores are just proportions!
What is the order when trying to find the area “between” and starting with the observations
First find z score then find area in Table A then subtract!
How to find normal distribution problem
- State the distribution that is of interest
- draw a normal curve with area shaded mean SDV in boundary lines
- Calculate do one of the following
either compute z score and table A to find area or use calculator and write down the common normal cdf
Steps for assessing normality problems
- graph it!
dot plot, histogram, see if it is symmetric or bell -shaped - Check the 68-95-99.7 rule
count the number of observations w/in 3 SDV negative and positive from the mean. Does the data follow? - Make a NPP with your calc
How to make a NPP(normal probability plot) w calc
2nd
Stat plot
1
On
Type NPP
Data list
L1
Axis X
Graph
Zoom
a(zoom stat)
How to center a graph?
Zoom 9
If trying to find ig Barack was unusually young when I agua rated look at
Cumulative frequency graph
Z score formula
Observation - mean / SDV
If u standardize all observations in a data set
Mean becomes 0 and SDV a becomes 1
If 6 houses sold for more and the total is 35 what does that mean
2 scored at or below so to find percentile it would be 29/35
What to use for center when data is skewed
Median
When using cumulative rel freq charts
Find median and IQR by look at decimal/percents on y axis
What are the 3 factors in a standard deviation problem
Center
Shape
Spread
0 z score = what percentile
50th
