Chapter 2 Stats Psych

Population

The collection of units (be the people, plankton, plants, cities, suicidal authors, etc) to which we want to generalize a set of findings or a statistical model

Sample

A smaller (but hopefully representative) collection of units from a population used to determine truths about that population

Mean

is the value from which the (squared) scored deviate least ( it has the least error)

Sample

Mean and SD describe only the sample from which they were calculated

Population

Mean and SD are intended to describe the entire population. (very rare in psychology)

Sample to population

Mean and SD are obtained from a sample but are used to estimate the mean and SD of the population (very common in psychology)

Mean squared error

The SS is a good measure of the accuracy of our model it depends on the amount of data collected

The standard error

SD tells us how well the mean represents the sample data

Null Hypothesis, H0

There is no effect

For example, Big Brother contestants and members of the public will not differ in their scores on personality disorder questionnaires

The alternative hypothesis, H1

Aka the experimental hypothesis

For example, Big Brother contestants will score higher on personality disorder questionnaires than members of the public

Test Statistics

A statistics for which the frequency of particular values is known

Observed values can be used to test hypotheses

Type 1 Error

Occurs when we believe that there is genuine effect in our population, when in fact there isn’t

The probability is the a-level (usually 0.05)

Type 2 error

Occurs when we believe that there is no effect in the population when, in reality, there is

The probability is the B-level (often 0.2)