Flashcards in Stat - Exam #1 Deck (134)
Why can’t observational studies determine causation?
-Because of possible lurking variables;
-Lurking = No measure, but DO affect the results (EX: Snoring and a risk of heart attack)
What does an experiment mean in statistics?
-High level of control;
-Often takes more than one study to eliminate or control lucking variables
What is an Experimental Unit?
An individual in a sample
What is Treatment?
A A condition of interest that is applied to the experimental unit
What is the Response Variable?
A quantitative or qualitative variable that reflects the characteristic of interest
What is a Double Blind study?
Neither the researcher nor the experimental unit knows whether, or what, treatment is being applied
What is a Placebo?
-A false treatment that has NO effect;
-Used to prevent experimental units from knowing whether they are being treated
How do I describe a column of data?
Distribution of data gives SHAPE, LOCATION, and SPREAD;
-These are very useful in abstracting the info from the data
What is the process of statistics?
1. Ask question;
2. Collect data = census, observational study, experimental design, or existing data;
3. Organize and analyze = overview with tables/graphs; detailed using methods depending on type;
4. Make a conclusion
What is Raw Data?
Data NOT organized
How is a variable (column of data) described?
-Condense and described by distribution;
-Distribution described by shape, location, and spread =
— Graphical methods determine shape;
— Numerical methods find location and spread
How can Qualitative data be graphically summarized?
-Frequency table and in a Graph (bar chart, pareto chart, and pie chart);
-Frequency organizes = shows what possible VALUES a variable take and HOW OFTEN each value;
-Picture give better overview
What is Frequency Table?
A table that lists all categories of data, with number of occurrences for each category;
-5 Columns =
3. Relative Frequency
4. Cumulative Frequency
5. Cumulative Relative Frequency
What is Category?
Lists the names of all categories in a column of data
What is Frequency?
The number of observations in each category
What is Relative Frequency?
The percent, or proportion, of data in each category;
Relative Frequency = (Frequency/Sum of all Frequencies)
What is Cumulative Frequency?
The sum of frequency up through, and including category of interest;
-the number of observations less than or equal to the category value
What is Cumulative Relative Frequency?
The sum of relative frequency up through and including the category of interest
What is a Bar Chart?
A graph of a set of data made with:
1. Categories on horizontal axis
2. Frequencies on vertical axis;
3. Rectangle of equal width (bar) drawn for each category with the hight equal to the category’s frequency (or relative frequency);
-Bars do NOT touch;
- Value are in the middle of the bars
What is a Pareto Chart?
A bar chart whose bars are drawn in descending order of height
What is a Pie Chart?
A circle divided in to wedges, where each wedge represents a category and the size of the wedge represents the relative frequency of a category;
-Summarizes qualitative data
How is Discrete Data summarized?
-Values are used to create categories;
-Histogram bar DO touch;
-Values marked in the middle of the bars
How do you graphically represent Continuous Data?
-Too many categories since each number is its own category;
-To condense, need to GROUP data into intervals and create new, smaller categories;
1. Group into classes; make a frequency table; make a histogram;
2. Or make a stem-and-leaf plot
What is the method to group Continuous data into classes?
1. Decide on the number of intervals (5-20).
2. Find the width of each interval (divide range by number of intervals)
3. Select a starting point for the first interval (usually the min)
4. Make the remaining intervals equidistant from start = equal widths, adjacent, no overlap, and convenient endpoints
What is a Histogram for CONTINUOUS data?
-Graph of a set of data made like a bar chart, but:
1. Bars DO touch;
2. The lower limit of each class is marked at the LEFT of each rectangle
What is a Stem-and-Leaf Plot?
-Graph to summarize continous data by dividing each data point into a star and and a leaf part and listing these parts
What is the method to make a Stem-and-Leaf Plot?
1. Rank the data from low to high;
2. Divide each point into stem and leaf;
-Leaf = rightmost digit
-Stem = digits to the left of leaf;
3. Write stems vertically from low to high;
4. Draw line to right of numbers;
5. Write the leaf next to the corresponding stem
How are distribution SHAPES described?
How are histograms analyzed?
1. Overall shape (frequency curve);
2. Any deviation from general shape