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PSY 1950Delphine S. Courvoisier

Harvard UniversityTAs: Stephanie McMains

Joseph McIntyre

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Potential mistakes (instructor is Swiss)• Temple, Bangkok : IT IS FORBIDDEN TO ENTER A WOMAN, EVEN A

FOREIGNER, IF DRESSED AS A MAN.• Cemetery: PERSONS ARE PROHIBITED FROM PICKING FLOWERS FROM

ANY BUT THEIR OWN GRAVES• Restaurant, Switzerland: OUR WINES LEAVE YOU NOTHING TO HOPE FOR.• Hotel, Japan: YOU ARE INVITED TO TAKE ADVANTAGE OF THE

CHAMBERMAID.• Hotel, Zurich : BECAUSE OF THE IMPROPRIETY OF ENTERTAINING GUESTS

OF THE OPPOSITE SEX IN THE BEDROOM, IT IS SUGGESTED THAT THE LOBBY BE USED FOR THIS PURPOSE.

• Airline ticket office, Copenhagen: WE TAKE YOUR BAGS AND SEND THEM IN ALL DIRECTIONS.

• Laundry, Rome : LADIES, LEAVE YOUR CLOTHES HERE AND SPEND THE AFTERNOON HAVING A GOOD TIME

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Information• Lectures (Mon and Wed 1-2:30, WJH 1305)

– Ex-cathedra presentations– Small quizzes– Reading of recent articles– Writing of abstract and methods/results sections

• Lab sessions (Tue 5-6:30,WJH 1305)

– Learning how to input and analyze data

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Information and schedule

• Course websitehttp://isites.harvard.edu/k89723

• Reading (compulsory)– Field, A. (2009). Discovering statistics using SPSS

(3rd edition). London: Sage. • Reading (non compulsory; good short refresher)

– Petrie, S., Sabin, C. (2009). Medical Statistics at a Glance (3rd edition). Sussex: Wiley.http://www.medstatsaag.com/

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Exam and grade

– 20% participation– 20% exercises– 25% mid-term test– 35% final exam

• Mid-term and final exam are an analysis of data given one week before the test, and questions asked on the analysis.

• For an example, see folder exam on isites

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Lecture 1

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Why do you need statistics?

• Duh!! To pass the exam• To understand the methods of data analysis

used in scientific articles for (applied) psychologists and for researchershttp://www.jsur.org/v1n1p1

• To apply this knowledge to critical reading of scientific articles in your professional life (continued training)

• To apply this knowledge to your own research

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Top 10 reasons to be a statistician1. Deviation is considered normal2. We feel complete and sufficient3. We are 'mean' lovers4. Statisticians do it discretely and continuously5. We are right 95% of the time6. We can legally comment on someone's posterior

distribution7. We may not be normal, but we are transformable8. We never have to say we are certain9. We are honestly significantly different10. No one wants our jobs

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Structure of an article

• Title

• Summary (structured)

• Body:– Introduction

– Methods

– Results

– Discussion

• References

Why do the study

How was the study done

What was observed

What does it mean

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Goal of statistical analysis

• Describe data

• Draw general conclusions about the world and its workings

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Question

• You collect scores on the BDI (a 21-question multiple-choice self-report depression inventory) from a sample of children. In your research:a) Depression is a discrete variableb) Depression is a continuous variablec) Depression is a ratio variabled) Depression is an interval variablee) It depends on how you think about depressionf) It depends on how you analyze the data

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Constructs and variables

• Constructs are theoretical concepts• Variables are the proxy used to measure those

constructs

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Question

• You collect fMRI data from 10’000 individuals on a sustained attention task linked to ADHD, and plot the results (DV = % signal change) in a histogram. The distribution is very close to normal. These results:a) provide strong evidence against a dichotomous

view of ADHD.b) could easily have arisen even if ADHD were a

dichotomous phenomenon.

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Median vs. mean

• Q: If you were to take 10,000 samples of n=25 from the below population and, for each sample, calculate its mean and median, how would the distributions of those two statistics vary from each other

• http://onlinestatbook.com/stat_sim/sampling_dist/index.html

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QuestionThese distributions differ in:a)Shapeb)Dispersionc)Neither shape nor

dispersiond)Both shape and

dispersion

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QuestionThese distributions differ in:a)Shapeb)Dispersionc)Neither shape nor

dispersiond)Both shape and

dispersion

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Question

• Using (http://onlinestatbook.com/stat_sim/sampling_dist/index.html) which of the following statements is true:a) When sampling from normal distributions, the

median is an unbiased statistic.b) When sampling from skewed distributions, the

median is a biased statistic.c) both a and b

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Graphical representations• Histogram (sorted bar chart)

• Box-plot

• Scatterplot

• Principles:– Have a clear visual message

– Promote visual comparisons

– Don’t cheat (axes, distortions, etc)

– Show all the data

– High ratio information/ink

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Tendency to use “round” numbers

median

mode: 170

mean

Histogram

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Boxplot

Smallest value

median

1st quartile

3rd quartile

outliers

¼

¼

¼

¼

Inter-quartile range

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Percentiles and boxplots

Xp50 p75p25

4 equal areas

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Scatterplot, central tendency and dispersion

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Interaction plots

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How many statisticians does it take to change a light bulb?

• With what degree of certainty do you need to know?