PSY 1950 Delphine S. Courvoisier Harvard University TAs: Stephanie McMains Joseph McIntyre 1

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 2

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 3

Information and schedule Course website Reading (compulsory) – Field, A. (2009). Discovering statistics using SPSS (3 rd edition). London: Sage. Reading ( non compulsory; good short refresher ) – Petrie, S., Sabin, C. (2009). Medical Statistics at a Glance (3 rd edition). Sussex: Wiley

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 5

Lecture 1 6

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 researchers  To apply this knowledge to critical reading of scientific articles in your professional life (continued training) To apply this knowledge to your own research 7

Top 10 reasons to be a statistician 1.Deviation is considered normal 2.We feel complete and sufficient 3.We are 'mean' lovers 4.Statisticians do it discretely and continuously 5.We are right 95% of the time 6.We can legally comment on someone's posterior distribution 7.We may not be normal, but we are transformable 8.We never have to say we are certain 9.We are honestly significantly different 10.No one wants our jobs 8

9 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

10 Goal of statistical analysis Describe data Draw general conclusions about the world and its workings

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 variable b)Depression is a continuous variable c)Depression is a ratio variable d)Depression is an interval variable e)It depends on how you think about depression f)It depends on how you analyze the data 11

Constructs and variables Constructs are theoretical concepts Variables are the proxy used to measure those constructs 12

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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. 14

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 _dist/index.html _dist/index.html 15

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Question These distributions differ in: a)Shape b)Dispersion c)Neither shape nor dispersion d)Both shape and dispersion 18

Question These distributions differ in: a)Shape b)Dispersion c)Neither shape nor dispersion d)Both shape and dispersion 19

Question Using ( _dist/index.html) which of the following statements is true: _dist/index.html 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 20

21 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

Tendency to use “round” numbers median mode: 170 mean Histogram 22

23 Boxplot Smallest value median 1 st quartile 3 rd quartile outliers ¼ ¼ ¼ ¼ Inter-quartile range

24 Percentiles and boxplots X p50p75p25 4 equal areas

Scatterplot, central tendency and dispersion 25

Interaction plots 26

How many statisticians does it take to change a light bulb? With what degree of certainty do you need to know? 27