Statistics test 1

Construct

topic you are actually studying, in psych this could look like measuring fear or happiness

statistics

a set of methods and rules or organizing, summarizing, and interpreting information (data)

population

set of individuals of interest in a study, vary in size; often quite large

sample

set of individuals selected from a population usually intended to represent the population in a research study (ex: 500 registered voters)

variable

characteristic/condition or has different values different individuals

data(plural)

measurements/obervations of a variable

Data set

collection of measurements or observations

datum (singular)

a single measurement or observation (aka raw score/score)

Descriptive stats

summarize, organize, and simplify data (tables, graphs, averages)

Inferential stats

study samples to make generalizations about the populations from which they were selected (interpret experimental data)

sampling error

amount of error between a sample stat and the corresponding parameter

parameter

a value, usually a numerical value that describes a population

discrete variables

has separate, individual categories. no values can exist between two neighboring categories (ex: number of children in a household)

continuous variable

has an infinite number of possible values between any two observed values. is divisible into an infinite number of fractional parts (ex: weight, height, temperature)

Scales of measurement

Nominal, ordinal, interval, ratio

Nominal

label and categorize, no quantitative distinctions (ex: gender, diagnosis, etc.)

Ordinal

categories observations that are organized by size or magnitude (ex: rank in class, clothing sizes—S,M,L,XL)

interval

ordered categories with an interval between categories of equal size. arbitrary or absent zero point (ex: temperature, IQ, etc.)

Ratio

ordered categories with equal intervals between categories and an absolute zero point (0 = nothing) (ex: number of correct answers, time to complete a task, etc)

correlational method

can demonstrate the existence of a relationship between two variables but does not explain the relationship, no cause and effect

experimental method

demonstrates a cause and effect relationship between two variables (independent and dependent)

Independent variable

variable that is manipulated by the researcher, no other variable in the study influences its value (ex: hours of sleep, alcohol consumption, type of psychotherapy)

Dependent variable

variable that is observed to assess the effect of the treatment, its value is thought to depend on the IV (ex: exam score, reaction time, level of depression)

summation

done after operations in parenthesis, squaring, and multiplication/division but done before addition/subtraction

constructing a frequency table

1) make a list of each possible value of the variable. if the variable is quantitative \, start with the highest number and put it at the top of the table

2) go one by one through the scores tallying how many responses in that category

3) make a table indicating the frequency of each variable

proportions/relative frequency

p = f/n, measures the fraction of the total group that is associated with each score

percentages

p= f/n(100), express relative frequency out of 100, can be included as a separate column in a frequency distribution table

cumulative frequency

cf = cf/N, sum of all the frequencies of all scores at or below a particular score, a running total

Symmetrical distribution

each side is a mirror image of the other

skewed distribution

scores pile up on one side and taper off in a tail on the other (tail on the right = positive skew, tail on the left = negative skew)

central tendency

statistical measure of a single score that defines the center of a distribution, its purpose is to find the single score that is most typical or most representative of the entire group

mean

the sum of all scores divided by the number of scores, balance point of distribution

median

midpoint of all the scores in a distribution when they are listed in order from smallest to largest, defined by the number of scores

mode

score or category that has the greatest frequency of any score in a frequency distribution, can be used with any scale of measurement, corresponds to an actual score in the data, is possible to have more than one