What is statistics?
•a branch of mathematics that provides techniques to analyze whether or not your data is significant (meaningful)
•Statistical applications are based on probability statements
•Nothing is “proved” with statistics
•Statistics are reported
•Statistics report the probability that similar results would occur if you repeated the experiment
Statistics deals with numbers :
•Need to know nature of numbers collected
–Continuous variables: type of numbers associated with measuring or weighing; any value in a continuous interval of measurement.
•Examples:
–Weight of students, height of plants, time to flowering
–Discrete variables: type of numbers that are counted or categorical
•Examples:
–Numbers of boys, girls, insects, plants
Can you figure out…
•Which type of numbers (discrete or continuous?)
–Numbers of persons preferring Brand X in 5 different towns
–The weights of high school seniors
–The lengths of oak leaves
–The number of seeds germinating
–35 tall and 12 dwarf pea plants
–Answers: all are discrete except the 2nd and 3rd examples are continuous.
Populations and Samples:
•Population includes all members of a group
–Example: all 9th grade students in America
–Number of 9th grade students at SR
–No absolute number
•Sample
–Used to make inferences about large populations
–Samples are a selection of the population
–Example: 6th period Accelerated Biology
•Why the need for statistics?
–Statistics are used to describe sample populations as estimators of the corresponding population
–Many times, finding complete information about a population is costly and time consuming. We can use samples to represent a population.
Sample Populations avoiding Bias:
•Individuals in a sample population
–Must be a fair representation of the entire pop.
–Therefore sample members must be randomly selected (to avoid bias)
–Example: if you were looking at strength in students: picking students from the football team would NOT be random
Is there bias?
•A cage has 1000 rats, you pick the first 20 you can catch for your experiment
•A public opinion poll is conducted using the telephone directory
•You are conducting a study of a new diabetes drug; you advertise for participants in the newspaper and TV
•All are biased: Rats-you grab the slower rats. Telephone-you call only people with a phone (wealth?) and people who are listed (responsible?). Newspaper/TV-you reach only people with newspaper (wealth/educated?) and TV( wealth?).
(Statistical Computations (the Math:
•If you are using a sample population
–Arithmetic Mean (average)
–The mean shows that ½ the members of the pop fall on either side of an estimated value: mean
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