Research MethodsResearch Methods

APA Ethical GuidelinesAPA Ethical Guidelines

Human Drug Trials

The APAThe APA – American Psychological – American Psychological Association Association

Responsible for setting the ethical Responsible for setting the ethical guidelines for human and animal guidelines for human and animal research.research.

The IRBThe IRB – Institutional Review Board – Institutional Review Board Part of the APA responsible for Part of the APA responsible for

reviewing research proposals for ethical reviewing research proposals for ethical violations and/or procedural errors. violations and/or procedural errors.

Human ResearchHuman Research

Research involving human Research involving human subjects must meet the subjects must meet the following standards:following standards:

1. Informed Consent1. Informed Consent–Participants must Participants must know that they are know that they are involved in research involved in research and give their and give their consent.consent.

2. Coercion2. Coercion–Participation in a Participation in a research study research study must be must be voluntary.voluntary.

3. Anonymity/Confidentiality3. Anonymity/Confidentiality– The participant’s privacy must be The participant’s privacy must be protected. No identities and protected. No identities and actions may be revealed. A actions may be revealed. A researched must not share any researched must not share any results that could match a results that could match a participant and their specific participant and their specific responses. A researcher will not responses. A researcher will not identify the source of any data as identify the source of any data as well.well.

4. Risk4. Risk–Participants Participants cannot be placed cannot be placed at any significant at any significant mental or mental or physical risk.physical risk.

5. Debriefing 5. Debriefing ProceduresProcedures–Participants must be told Participants must be told the purpose of the study the purpose of the study and provided with ways to and provided with ways to contact the researcher contact the researcher about the study results.about the study results.

Animal ResearchAnimal Research

Ethical studies using Ethical studies using laboratory animals must laboratory animals must meet the following meet the following requirements:requirements:

1. The must have a clear 1. The must have a clear scientific purpose.scientific purpose.–The research must answer a The research must answer a specific, important scientific specific, important scientific question. Animals are question. Animals are chosen based on their ability chosen based on their ability to help answer the question to help answer the question proposed.proposed.

2. The animals 2. The animals must be cared for must be cared for and housed in a and housed in a humane way.humane way.

3. The animal subjects must 3. The animal subjects must be acquired in a legal manner.be acquired in a legal manner.–The animals used in the The animals used in the experiment must be purchased experiment must be purchased from accredited companies, and from accredited companies, and if trapped in the wild, they must if trapped in the wild, they must be trapped in a humane be trapped in a humane manner.manner.

4. The experiment must 4. The experiment must be designed with be designed with procedures in place that procedures in place that employ the least employ the least amount of suffering on amount of suffering on the part of the animals.the part of the animals.

How do How do psychologists psychologists collect data collect data

about behavior?about behavior?

Regardless of the method Regardless of the method used, all research is used, all research is based on the Scientific based on the Scientific Method of PsychologyMethod of Psychology

ScientificScientific means systematic, means systematic, testable, and objective.testable, and objective.

What are the What are the main principles main principles that guide the that guide the

Scientific Method Scientific Method of Psychology?of Psychology?

Step 1 – Review the existing Step 1 – Review the existing Literature Literature

Step 2 – Develop a testable Step 2 – Develop a testable Hypotheses Hypotheses

Step 3 – Research and ObservationStep 3 – Research and Observation Step 4 – Analyze the data Step 4 – Analyze the data Step 5 – Publish, Replicate, Seek Step 5 – Publish, Replicate, Seek

Review Review Step 6 – Build a TheoryStep 6 – Build a Theory

Step 1Step 1

Review the existing Review the existing literature. What studies literature. What studies have already been have already been completed? What are the completed? What are the current theories and data current theories and data indicating about behavior?indicating about behavior?

Step 2Step 2

A hypothesis is then created A hypothesis is then created as a testable prediction as a testable prediction based on what is currently based on what is currently known and what we want to known and what we want to find out. What do we want find out. What do we want to know more about?to know more about?

Step 3Step 3

Experiments, surveys, Experiments, surveys, observations, case-observations, case-studies, etc. are studies, etc. are generated to collect generated to collect data.data.

Step 4Step 4

The raw data is organized The raw data is organized and needs to be evaluated. and needs to be evaluated. Statistics may be used to Statistics may be used to organize, summarize, and organize, summarize, and interpret the numerical data. interpret the numerical data. Does the data support, or not Does the data support, or not support, the hypothesis?support, the hypothesis?

Step 5Step 5

The results should be shared The results should be shared with other researchers in a peer-with other researchers in a peer-reviewed journal. Other reviewed journal. Other researchers may choose to researchers may choose to replicatereplicate (repeat) the study to (repeat) the study to check for validity, or to further check for validity, or to further explain or explore some aspects explain or explore some aspects of the study.of the study.

Step 6Step 6

After one or more studies After one or more studies on a given topic, on a given topic, researchers may advance a researchers may advance a theorytheory (current (current knowledge/concepts that knowledge/concepts that explain a body of data), or explain a body of data), or challenge a theory.challenge a theory.

What are the two What are the two broad types of broad types of research that research that psychologists psychologists

conduct?conduct?

Research DesignsResearch Designs

QuantitativeQuantitative and and Qualitative Qualitative ResearchResearch

Quantitative ResearchQuantitative Research usually involves usually involves experimentation or experimentation or correlation studies, and the correlation studies, and the datadata produces numbers, produces numbers, measurements, deductive measurements, deductive logic, statistics, etc.logic, statistics, etc.

.

Qualitative ResearchQualitative Research emphasizes natural settings emphasizes natural settings and observation, and and observation, and generates data in the form generates data in the form of written themes, verbal of written themes, verbal narratives, personalized narratives, personalized comments, pictures, etc.comments, pictures, etc.

What are What are examples of a examples of a

qualitative qualitative research research methods?methods?

I. Naturalistic ObservationI. Naturalistic Observation

Researchers study Researchers study spontaneous and spontaneous and natural behaviors in a natural behaviors in a subjects most familiar subjects most familiar environment. There environment. There is no interaction with is no interaction with the subject during the subject during these observations.these observations.

Researcher BiasResearcher Bias

Situation in which a Situation in which a personal factor unfairly personal factor unfairly increases the likelihood increases the likelihood of a researcher reaching a of a researcher reaching a particular conclusionparticular conclusion

Example of BiasExample of Bias

I was recently mugged by a I was recently mugged by a group of teenagers, or I just had group of teenagers, or I just had a fight with my teenage son over a fight with my teenage son over driving privileges. My driving privileges. My assignment is to observe assignment is to observe teenage behaviors at the mall. teenage behaviors at the mall. Will I be more inclined to seek Will I be more inclined to seek out bad behaviors or infer bad out bad behaviors or infer bad intentions and motivations? intentions and motivations?

Participant BiasParticipant Bias

The tendency of research The tendency of research subjects to respond in certain subjects to respond in certain ways because they know they ways because they know they are being observed. The are being observed. The subjects might try to behave in subjects might try to behave in ways they believe the ways they believe the researcher wants them to researcher wants them to behave.behave.

The The Hawthorne EffectHawthorne Effect refers refers to the fact that some subjects to the fact that some subjects will alter their behaviors will alter their behaviors simply because they know simply because they know that they are part of an that they are part of an experiment, regardless of experiment, regardless of what is being done to them.what is being done to them.

II. Case StudyII. Case Study

A case study is a situation in A case study is a situation in which a single individual is which a single individual is studied in-depth by a studied in-depth by a researcher, often times due to researcher, often times due to their unique behaviors or their unique behaviors or situation. Case studies are very situation. Case studies are very interactive and often include interactive and often include face-to-face interviews, paper face-to-face interviews, paper and pencil tests, the study of and pencil tests, the study of medical records, etc.medical records, etc.

Police have arrested Bart for Police have arrested Bart for the serial killing of fifteen the serial killing of fifteen young women over the past young women over the past ten years. A psychiatrist ten years. A psychiatrist will examine the police files, will examine the police files, medical files, observe and medical files, observe and interview Bart, talk to his interview Bart, talk to his and the victims families, and the victims families, friends, etc. in order to friends, etc. in order to understand Bart’s behaviors understand Bart’s behaviors and motivations.and motivations.

What is the best What is the best example of a example of a

research method that research method that produces both produces both

quantitative and quantitative and qualitative data?qualitative data?

III. SurveyIII. Survey

Questionnaires/ interviews. Questionnaires/ interviews. Using a combination of Using a combination of forced and open response forced and open response questions, it can be helpful in questions, it can be helpful in analyzing and predicting analyzing and predicting behaviors.behaviors.

Advantageous because you Advantageous because you gather a large amount of gather a large amount of information from a large information from a large group of people.group of people.

False Consensus EffectFalse Consensus Effect

Tendency to overestimate Tendency to overestimate the extent to which others the extent to which others share our beliefs and share our beliefs and behaviors. Skews the behaviors. Skews the reports by jumping to large reports by jumping to large conclusions that fit into our conclusions that fit into our pre-conceived ideas.pre-conceived ideas.

Which types of Which types of research produce research produce

primarily primarily qualitative data?qualitative data?

IV. ExperimentIV. Experiment

An investigation seeking to An investigation seeking to understand relations of understand relations of cause cause and effectand effect. The experimenter . The experimenter changes a variable (cause), and changes a variable (cause), and in turn changes another variable in turn changes another variable (effect). At the same time the (effect). At the same time the experimenter hopes to hold all of experimenter hopes to hold all of the other variables constant so the other variables constant so that they can attribute any that they can attribute any changes to only the manipulation.changes to only the manipulation.

IE. I want to know if new Drug A will help IE. I want to know if new Drug A will help to alleviate the symptoms of insomnia. I to alleviate the symptoms of insomnia. I can manipulate the dosage and the times, can manipulate the dosage and the times, but I need to control other factors like but I need to control other factors like mattress softness, diet and room mattress softness, diet and room temperature to eliminate them as variables temperature to eliminate them as variables that affect sleep. At the end of the that affect sleep. At the end of the experiment I want to know that it was only experiment I want to know that it was only Drug A that affected the patient’s sleep.Drug A that affected the patient’s sleep.

How do I How do I create a create a valid and valid and reliable reliable

experimenexperiment?t?

Step 1: Choose a Step 1: Choose a HypothesisHypothesis

A hypothesis expresses a A hypothesis expresses a relationship between two relationship between two variables. variables.

IE. My hypothesis is that IE. My hypothesis is that watching violent television watching violent television programs makes people more programs makes people more aggressive.aggressive.

Step Two: Choose VariablesStep Two: Choose Variables

Variables are things Variables are things that are measured, that are measured, controlled, or controlled, or manipulated in manipulated in research.research.

The The independent independent variablevariable is the is the manipulated variablemanipulated variable..

IE. The violent IE. The violent programming is the programming is the independent variable independent variable because I can adjust what because I can adjust what shows are viewed, for shows are viewed, for how long, by whom, etc.how long, by whom, etc.

The The dependent variabledependent variable is is measured for change.measured for change.

IE. Measuring the change in IE. Measuring the change in aggression levels is the aggression levels is the dependent variable in our dependent variable in our experiment because it experiment because it changes based on what is changes based on what is viewed, for how long, etc.viewed, for how long, etc.

Step Three: OperationalizeStep Three: Operationalize

When you When you operationalizeoperationalize your your variables, you are variables, you are explaining how you explaining how you will will measuremeasure them. them.

IE. The operational definition of the IE. The operational definition of the independent variable (what defines a violent independent variable (what defines a violent show?) would be shows that have scenes of show?) would be shows that have scenes of fighting, bloodshed, use of weapons, injury, fighting, bloodshed, use of weapons, injury, kicks, punches, etc.kicks, punches, etc.

IE. The operational definition of the IE. The operational definition of the dependent variable (what constitutes an dependent variable (what constitutes an increase in aggressive behavior?) would be increase in aggressive behavior?) would be an increase in agitation or tenseness, an increase in agitation or tenseness, increased vocal volume, threats of bodily increased vocal volume, threats of bodily harm, kicks, punches, throwing objects, etc.harm, kicks, punches, throwing objects, etc.

Step Four: Identify Potential Step Four: Identify Potential Extraneous Variables/Confounding Extraneous Variables/Confounding

VariablesVariables It is important to make sure that It is important to make sure that

during the experiment as many during the experiment as many other factors that are NOT part of other factors that are NOT part of the therapy are NOT included. the therapy are NOT included. Any factor or variable that causes Any factor or variable that causes an effect (or potential affects) an effect (or potential affects) other than the variable being other than the variable being studied is considered an studied is considered an extraneous variable.extraneous variable.

IE. An extraneous variable in our IE. An extraneous variable in our experiment would be a phone call experiment would be a phone call from a solicitor during a program, from a solicitor during a program, the viewer receiving mail including a the viewer receiving mail including a poor report card, a viewer stubbing poor report card, a viewer stubbing their toe during a show, alcohol their toe during a show, alcohol abuse, etc. All of these could abuse, etc. All of these could increase aggressiveness, but are not increase aggressiveness, but are not related to viewing violent television.related to viewing violent television.

Step Five: Identify Who You Will Be TestingStep Five: Identify Who You Will Be Testing

The people on which the The people on which the research will be conducted research will be conducted are called are called participants. participants. If If you are using animals, they you are using animals, they are referred to as are referred to as subjectssubjects..–I want to test the effects of I want to test the effects of television violence on television violence on teenage behaviors.teenage behaviors.

Step Six: How Do We Decide Step Six: How Do We Decide Who Will Be Subjects, and Who Who Will Be Subjects, and Who

Won’t?Won’t?Since we can’t realistically Since we can’t realistically

test all teenagers in the test all teenagers in the world (world (the test populationthe test population), ), we must reduce the overall we must reduce the overall population down to a more population down to a more manageable number (manageable number (the the test sampletest sample). How?). How?

Method 1: Rigorous Control Method 1: Rigorous Control DesignDesign

Designing an experiment Designing an experiment with specific, hand-picked with specific, hand-picked participants in mind. participants in mind. –IE. Only testing males, 18 IE. Only testing males, 18 years old, enrolled in AP years old, enrolled in AP Psychology at Middletown Psychology at Middletown High School.High School.

Method 2: Random SampleMethod 2: Random Sample

A A random samplerandom sample allows allows that that everyevery member of an member of an overall population has overall population has an equal chance to be in an equal chance to be in the sample.the sample.

IE. Put all teenager’s names IE. Put all teenager’s names into a hat and pull out fifty into a hat and pull out fifty names.names.

Method 3: Systematic Method 3: Systematic SampleSample

Select a starting point from your Select a starting point from your population and then select every population and then select every ?th participant.?th participant.– Alphabetically list all teenagers Alphabetically list all teenagers

from one to one million, and then from one to one million, and then choose every 10choose every 10thth name on the list name on the list to be a participant in the to be a participant in the experiment.experiment.

Step Seven: AssignmentStep Seven: Assignment

Once you have chosen Once you have chosen your subjects to study, your subjects to study, you must assign them to you must assign them to one of two groups; those one of two groups; those that will be manipulated, that will be manipulated, and those that won’t.and those that won’t.

Group 1: Experimental Group 1: Experimental GroupGroup

The The experimental experimental groupgroup receives the receives the independent variable independent variable and is manipulated and is manipulated throughout the throughout the experiment.experiment.

IE. In our television violence IE. In our television violence experiment, those in the experiment, those in the experiment group will watch experiment group will watch varying degrees of violent varying degrees of violent program, for varying lengths of program, for varying lengths of time, etc., and their changes in time, etc., and their changes in levels of aggression measured.levels of aggression measured.

Group 2: Control GroupGroup 2: Control Group

The The control groupcontrol group does not receive does not receive the independent the independent variable. They are variable. They are the used for the used for comparative comparative purposes.purposes.

IE. In our television violence IE. In our television violence experiment, the control group will be experiment, the control group will be shown a variety of non-violent shown a variety of non-violent programming in order to create a programming in order to create a baseline to compare the experiment baseline to compare the experiment group against. group against.

How do the behaviors of teens How do the behaviors of teens exposed to non-violent programming exposed to non-violent programming compare with those of teens who compare with those of teens who watch violent programming?watch violent programming?

Random AssignmentRandom Assignment

Random assignmentRandom assignment means means that the subjects have an equal that the subjects have an equal chance of being placed into chance of being placed into each group. If we allow each group. If we allow subjects to choose their own subjects to choose their own group, we may have a group, we may have a subject-subject-relevant confounding variablerelevant confounding variable..

Subject-Relevant Confounding Subject-Relevant Confounding VariablesVariables

A A subject-relevant confounding subject-relevant confounding variable variable would allow those would allow those people that liked violent movies people that liked violent movies or were prone to violence or were prone to violence already to choose to be in the already to choose to be in the experimental group. We experimental group. We therefore could not accurately therefore could not accurately find that viewing violence find that viewing violence directly led to their aggression.directly led to their aggression.

To help avoid this To help avoid this confounding variable, we confounding variable, we prescribe a prescribe a single-blind single-blind designdesign. The subjects do . The subjects do not know whether they not know whether they have been randomly have been randomly placed in the control or placed in the control or experiment group.experiment group.

Group MatchingGroup Matching

When assigning members When assigning members to the experiment or to the experiment or control group, it is control group, it is important that the important that the characteristics of both characteristics of both groups need to be as groups need to be as similar as possible.similar as possible.

IE. After rigorously or IE. After rigorously or randomly determining our randomly determining our subjects, as many white, subjects, as many white, black, tall, short, overweight, black, tall, short, overweight, slim members should be in slim members should be in the control group as there the control group as there are in the experiment group.are in the experiment group.

Experimenter BiasExperimenter Bias

Experimenter BiasExperimenter Bias occurs when the occurs when the experimenter unconsciously treats experimenter unconsciously treats members of the control and experiment members of the control and experiment groups differently, which increases the groups differently, which increases the chances of confirming their hypothesis.chances of confirming their hypothesis.

IE. The experimenter gives soda to the IE. The experimenter gives soda to the control group, and beer to the violent control group, and beer to the violent viewers. The experimenter speaks more viewers. The experimenter speaks more abruptly with the violence crowd (inciting abruptly with the violence crowd (inciting them?).them?).

To help avoid this type of To help avoid this type of confounding variable, we confounding variable, we employ a employ a double-blind designdouble-blind design, , where neither the subjects nor where neither the subjects nor the researcher may know the researcher may know which is the control or the which is the control or the experiment group. A third-experiment group. A third-party has the appropriate party has the appropriate records so that the date can records so that the date can be analyzed later.be analyzed later.

Other Things to Consider…Other Things to Consider…

The The Placebo EffectPlacebo Effect refers to refers to the phenomenon that a the phenomenon that a patient's symptoms can be patient's symptoms can be alleviated by an otherwise alleviated by an otherwise ineffective treatment, ineffective treatment, apparently because the apparently because the individual expects or individual expects or believes that it will work.believes that it will work.

Hindsight BiasHindsight Bias is the is the tendency to believe, tendency to believe, once the outcome is once the outcome is already known of course, already known of course, that you would have that you would have foreseen it…that even foreseen it…that even though it's over and you though it's over and you know the outcome, you know the outcome, you knew it all along.knew it all along.

REMEMBER !!!REMEMBER !!!

Only experimental data Only experimental data can conclusively can conclusively

demonstrate causal demonstrate causal relations between relations between

variables variables (A causes B to (A causes B to

happen).happen).

CorrelationCorrelation

Correlation StudyCorrelation Study

Research study designed to Research study designed to determine the degree to determine the degree to which two variables are which two variables are relatedrelated to one another. This to one another. This does not prove a cause and does not prove a cause and effect relationship; only that effect relationship; only that some relationship exists.some relationship exists.

How are exercise and How are exercise and weight related? Are weight related? Are smoking and rates of smoking and rates of cancer related? Is cancer related? Is there a relationship there a relationship between brain size and between brain size and intelligence? Does intelligence? Does your level of education your level of education have any implications have any implications on your potential on your potential future earnings?future earnings?

Types of Types of Correlation Correlation

RelationshipsRelationships

After you’ve After you’ve collected your data, collected your data, it’s time to organize it’s time to organize and analyze it.and analyze it.

Scatter plots consist of a large Scatter plots consist of a large body of data plotted on a graph body of data plotted on a graph to show their relationship to one to show their relationship to one another. The closer the data another. The closer the data points are to making a straight points are to making a straight line, the higher the correlation line, the higher the correlation between the two variables, or between the two variables, or the stronger the relationship.the stronger the relationship.

PositivePositive Correlation Correlation

As the value of one As the value of one variable increases so variable increases so does the value of the does the value of the other variable.other variable.

Studying and GradesStudying and Grades–As students study more, their grades As students study more, their grades

increase.increase.Practice and AthleticsPractice and Athletics

–As athletes practice more, their batting As athletes practice more, their batting averages increaseaverages increase

Driving Speed and DistanceDriving Speed and Distance–As drivers drive faster, they travel further.As drivers drive faster, they travel further.

A perfect positive correlation A perfect positive correlation results in a numerical value of results in a numerical value of 1.001.00

Positive correlations range Positive correlations range from 0.00 to 1.00. The closer from 0.00 to 1.00. The closer to 1.00 you get, the stronger to 1.00 you get, the stronger the positive correlation is.the positive correlation is.

NegativeNegative Correlation CorrelationAs the value of one As the value of one variable increases, variable increases, the value of the other the value of the other variable decreases.variable decreases.

–The more you exercise, the The more you exercise, the less you weighless you weigh

–The more you study, the less The more you study, the less your teachers yell at youyour teachers yell at you

–As the price of movie tickets As the price of movie tickets increases, the number of increases, the number of patrons decreases.patrons decreases.

A perfect negative A perfect negative correlation results in a correlation results in a numerical value of -1.00numerical value of -1.00

Negative correlations range Negative correlations range from 0.00 to -1.00. The from 0.00 to -1.00. The closer to -1.00 you get, the closer to -1.00 you get, the stronger the negative stronger the negative correlation is.correlation is.

ZeroZero Correlation CorrelationThere is no relationship There is no relationship

whatsoever between the two whatsoever between the two variables.variables.–The length of your hair has no The length of your hair has no

influence on your level of influence on your level of intelligence.intelligence.

No correlation No correlation relates to a relates to a numerical score of numerical score of 0.000.00

Correlation StudyCorrelation Study Important NOT to imply a cause and Important NOT to imply a cause and

effect relationship between the variableseffect relationship between the variablesCorrelational study does not determine Correlational study does not determine whywhy the two variables are related--just the two variables are related--just that they are related.that they are related.

Correlational studies are helpful in Correlational studies are helpful in making predictions.making predictions.

Illusory CorrelationIllusory Correlation

http://www.mensfitness.com/sports/http://www.mensfitness.com/sports/athletes/10-most-superstitious-athletes/10-most-superstitious-athletesathletes

Once I have Once I have completed my completed my

research, how do I research, how do I present my present my findings ?findings ?

Descriptive StatisticsDescriptive Statistics describe a set of data.describe a set of data.

I. Measures of Central I. Measures of Central TendencyTendency

Measures of central tendency provide Measures of central tendency provide statistics that indicate the average or statistics that indicate the average or typical score in the distribution. There are typical score in the distribution. There are three measures of central tendency: three measures of central tendency:

MeanMeanMedianMedianModeMode

MeanMean

The The meanmean is the is the arithmetic average of arithmetic average of all the scores in the all the scores in the distribution. distribution.

Regression to the MeanRegression to the Mean

In statistics, it is the In statistics, it is the phenomenon whereby members phenomenon whereby members of a population with extreme of a population with extreme values on a given measure for values on a given measure for one observation will probably one observation will probably give less extreme measurements give less extreme measurements on other occasions when they on other occasions when they are observed. are observed.

– IE. A running back rushed for 276 yards IE. A running back rushed for 276 yards in his first football game of the season. in his first football game of the season. More than likely he will not rush for More than likely he will not rush for 4416 yards that season (considering 4416 yards that season (considering only five players have ever rushed from only five players have ever rushed from more than 2,000 yards in a single NFL more than 2,000 yards in a single NFL season). It’s more likely that his game season). It’s more likely that his game totals will decrease and his overall totals will decrease and his overall average will eventually reflect an NFL average will eventually reflect an NFL average of about 67 yards per game. average of about 67 yards per game.

MedianMedian

The The medianmedian is the middle score is the middle score of the distribution, the point that of the distribution, the point that divides a rank-ordered divides a rank-ordered distribution into halves distribution into halves containing an equal number of containing an equal number of scores. Thus 50% of the scores scores. Thus 50% of the scores lie below the median and 50% lie lie below the median and 50% lie above the median.above the median.

ModeMode

The The modemode is simply is simply the score in the the score in the distribution that distribution that occurs most occurs most frequently.frequently.

Graphing Measures of Central Graphing Measures of Central TendencyTendency

Positively SkewedPositively Skewed

This distribution has a positive This distribution has a positive skew. Note that the mean is skew. Note that the mean is larger than the median.larger than the median.

IE. In a neighborhood of IE. In a neighborhood of relatively low incomes, a relatively low incomes, a few millionaires move in. few millionaires move in. Those few high salaries will Those few high salaries will inflate the mean inflate the mean (average), but the median (average), but the median will remain relatively low.will remain relatively low.

Negatively SkewedNegatively Skewed

This distribution has a negative This distribution has a negative skew. The median is larger than skew. The median is larger than the mean.the mean.

IE. In a particular well-to-do IE. In a particular well-to-do neighborhood, a few low-neighborhood, a few low-income residents move in. income residents move in. The overall average income The overall average income will drop a bit, but the will drop a bit, but the median will remain median will remain relatively high.relatively high.

When graphing the mean, When graphing the mean, median and mode of a median and mode of a distribution, roughly distribution, roughly speaking, a distribution has speaking, a distribution has positive skewpositive skew if the right if the right tail is longer and tail is longer and negative negative skewskew if the left tail is longer. if the left tail is longer.

II. Measures of VariabilityII. Measures of Variability

Measures of Measures of variability show how variability show how spread out the spread out the distribution of scores distribution of scores is from the mean.is from the mean.

Measures of VariabilityMeasures of Variability

RangeRangeStandard Standard DeviationDeviation

RangeRange

The The rangerange is simply the is simply the numerical difference numerical difference between the highest and between the highest and lowest scores in the lowest scores in the distribution. distribution.

Standard DeviationStandard Deviation

The measure of variability The measure of variability used most often in research used most often in research is the is the standard deviationstandard deviation,, a a statistic that indicates the statistic that indicates the average distance of the average distance of the scores from the mean of the scores from the mean of the distribution.distribution.

IE. Our class took Unit Exam 2. I IE. Our class took Unit Exam 2. I scored a 76%. I want to know how scored a 76%. I want to know how well I did in relation to the rest of the well I did in relation to the rest of the class to see whether or not that class to see whether or not that score was good or bad. I need to score was good or bad. I need to figure out what the class average figure out what the class average was, figure out the standard was, figure out the standard deviation from the mean, and I’ll deviation from the mean, and I’ll know how well I did.know how well I did.

Standard DeviationStandard Deviation

Graphing Standard Graphing Standard DeviationDeviation

Find the mean of your distribution set.Find the mean of your distribution set. Calculate the SD on your calculator.Calculate the SD on your calculator. The mean is set at “0”. The mean is set at “0”. +1 and -1 are your SD above and +1 and -1 are your SD above and

below the mean.below the mean.– IE. Your mean is 56 with a SD of 6. +1 IE. Your mean is 56 with a SD of 6. +1

would be 62, and -1 would be 50.would be 62, and -1 would be 50.– Calculate +- 2 and +- 3 in the same Calculate +- 2 and +- 3 in the same

manner.manner.

Graphing Standard Graphing Standard DeviationDeviation

What does this tell us?What does this tell us?– If the mean of a set of class scores on a If the mean of a set of class scores on a

unit exam was 72, with a SD of 8, 68% of unit exam was 72, with a SD of 8, 68% of students scored between a 64 and an 80. students scored between a 64 and an 80. Your score of a 76 would be close to being Your score of a 76 would be close to being better than 68% of the rest of the class. better than 68% of the rest of the class.

– Approximately 95% of the class scored Approximately 95% of the class scored between a 56 and an 88. Your score of a between a 56 and an 88. Your score of a 50 would indicated that roughly 96% of 50 would indicated that roughly 96% of the class did better than you on the test. the class did better than you on the test.