Statistics 2

To oversimplify, random selection is useful to _______, while random assignment is useful to _______.

"Assure that we can generalize to the population from which we sampled"; "Assure that differences between groups are not due to extraneous variables."

The most important characteristics behind using different scales is to keep in mind the numbers themselves. (T or F)

False. What is important is the underlying variable that we hope that we are measuring.

interval scale

The values of data measured on this scale can be rank ordered. In addition, the differences between two adjacent ranks are equal.

constant

a number that does not change in value in a given situation

nominal scale

a set of number assigned that frequently have no meaning other than as a label that distinguishes the variables. Data on this scale is measured by determining the category to which they belong.

scales of measurement

characteristics of relations among numbers assigned to objects

quantitative variables can be either

continuous or discrete

response variable

dependent variable, is the variable whose variation we are interested in. this is the variable that sually goes in the y axis of a graph

all categorical variable types are

discrete

what is the practical distinction between discrete and continuous variables

discrete variables take on only a few different values, but continuous variables can take on any value between the lowest and highest score

parameters are represented using

greek letters

ratio scale

has a true zero point. The values of data measured on this scale can be rank ordered and have meaningful differences between scale points.

what is the difference between an interval and a ratio scale

in the latter we can meaningfully speak of the ratio between numbers. but we will generally apply the same statistical procedures to both kinds of data

explanatory variable

independent variable, the variable that we believe is influencing the variation of the response variable. this is the variable that usually goes in the x axis of a graph

name the four common scales of measurement

nominal, ordinal, interval, ratio

ordinal scale

orders people, objects, or events along some continuum. The values of data measured on this scale can be rank ordered.

statistics are represented by

roman letters

rules of summation

sigma(x-y)=sigmax-sigmay; sigmacx=csigmax; sigma(x+c)=sigmax+Nc (N=number of items being summed

sigma

symbol indicating summation

random assignment

the allocation or assignment of participants to groups by a random process

measurement

the assignment of numbers to objects

true zero point

the point that corresponds to the absence of the thing being measured. 0 K

discrete variables

the variable can take on only a relatively few possible values

dependent variables

the variables being measured; the data or score

what is the independent variable

this is the variable that we are trying to study as opposed to the score that we obtain

independent variables

those variables controlled by the experimenter

continuous variables

variable could assume any value between the lowest and highest points on the scale.

quantitative variables

variables characterized by a numerical value; interval: numerical values in which the intervals between the values are assumed to be the same, ratio: numberical values with a meaningful zero point. zero represents the absence of the variable

categorical variables

aka qualitative variables; variables characterized as a set of categories. can be: nominal 2 or more categories. order does not matter; dichotomous: only 2 categories or levels order does not matter these are also nominal variables. ordinal: two or more categories, order matters categories can be ordered or ranked