Psychology Statistics Exam 1 Study Guide

What is sampling error?

an unibiased error that’s more likley to be above than below the true value

Four Scales of Measurement (NOIR)

1) Nominal

• is just used to name/list out

• is the weakest

• no actual order

2) Ordinal

• subjects are separated into categories

• has a ranking/order

• interval size is unknown

3) Interval

• has ranking

• has an equal interval size

• distance between points are equal

4) Ratio

• has a true zero

  • meaning there’s an absolute absence of something being measured

• has all the characteristics that the interval scale has

skewed distribution?

• data points aren’t evenly distributed around the mean

• is cluttered to one side

draw out a positive and negative skewed distribution

varaince definition?

• a measure of variability

• the degree to which scores in a distribution differ from the mean

what does variance tell about distribution?

variance tells how spread out data points are in a distribution

standard deviation (SD) definition?

a measure of the average amount in which scores deviate on either side of the mean

how does SD relate to variance?

SD is the square root of variance

what does SD tell approximately about a group of scores?

tells us how spread out a group of scores are from the mean

is SD or variance easier to grasp for variablity (opinionated)

n/a

discrete variable?

a variable that can only take a finite # of distinct values

• most of the time is whole #’s

• ex. number of objects in a jar

continuous variable?

a variable able to take on any number within a given range

• ex. weight

difference between experimental vs non-experimental/correlational

• an experimental study has an IV while non-experimental/correlational have a QIV

• the goal of an expeirmental is to try and establish causation

two elements need for an experiment to be achieved

1) independent variable manipulation

2) control group

symbol for frequency

f

symbol for cumulative frequency

cf

how to find cumulative percentage?

cumulative%= cf value/total of the frequency

grouped frequency table

• scores are grouped in class intervals

frequency distribution table

table that shows each score and the frequency it occurs at

what are the guidelines for selecting intervals in a grouped distribution table?

a) intervals:

• no overlap

• specific capture range (ex. 40-45)

b) decide the # of intervals

• need to capture important aspects of the shape

• ex. 5-15 interval

c) interval size:

• 2, 3, 5, or multiple of 5

how to find proportion?

p= f/n (frequency of score / total number of scores obtained)

what are the 3 measures of central tendency?

mean, median and mode (the three M’s)

mean

is the sum of scores divided by the number of scores

• mean = sum of X / N

median

the middle score

• in odd # obeservations:

  • median is the value at position

• in even # observations:

  • the avergae between the 2 values on either side of the position

mode

the most frequently occuring score (the highest frequency)

symbol for sample mean

x̄ (x-bar)

symbol for population mean

μ (mu)

symbol for populatuon size

N

symbol for sample size

n

symbol for population SD

σ (sigma)

symbol for sample SD

s

symbol for population variance

σ² (sigma squared)

symbol for sample variance

s²

when is it best to select the mean vs the median to reflect central tendency is a given distribution, especially when there are outliers in your data set

best to select the median for central tendency measurement

• why? because the median is not as affected by the outliers (extreme measurements) compared to the mean

population variance formula

sample variance formula

sample mean formula

z-score formula