GRAPPLING WITH DATA Variability in observations Sources of variability measurement error and reliability Visualizing the sample data Frequency distributions –Plotting frequency distributions –Types of distributions

FREQUENCY DISTRIBUTIONS bimodal normal skewed truncated

GRAPPLING WITH DATA Reducing and describing the sample Measures of central tendency –Mode: the most common score(s) –Median: the middle score –Mean: the “center of gravity” – sum / n Measures of dispersion –Range: largest minus smallest score –Variance: average squared deviation from mean

USING EXCEL FOR DESCRIPTIVE STATISTICS Entering data into a spreadsheet –Formatting numerical cells Generating frequency distributions –Scores go in “data array” –Categories go in “bins array” –Select cells adjacent to bins + 1 –Select Frequency formula, data and bin arrays –Press CTL+SHIFT+ENTER

USING EXCEL FOR DESCRIPTIVE STATISTICS Obtaining measures of central tendency –“by hand” –By using Excel formulas Obtaining measures of variability –Variance and standard deviation

TABLE ASSIGNMENT Obtain data file from web or lab Use Excel to calculate means, SD’s Construct table with those data for –Three tasks (simple form, color, complex form) –X four array sizes (4, 8, 16, 32) Format according to APA Style guide

Signal Detection Analysis “no” Response Criterion “yes” Target absent (noise) Target present (signal+noise)

SIGNAL DETECTION ANALYSIS Response: “YES”“NO” Stimulus Present hitsmisses Stimulus Absent falsecorrect alarmsrejections

Deriving d’ d’ = NORMSINV(prob hit) - NORMSINV(prob FA) In effect, the difference in “distance” of the mean of the normalized distributions for hits versus false alarms (!)

Signal Detection Analysis Vary % of trials with targets: 10%50%90% p(hit) p(FA) NormSI(h) NormSI(fa) d’ Conclusion: likelihood of a “signal” affects response criterion (or “bias”), not “sensitivity” to the signal.

FIGURE ASSIGNMENT Derive d’s from Hits & False alarm rates in Lab 5 Construct an APA-formatted Figure with: –Mean d’ for 2 durations x 2 frame stimuli –Error bars indicating standard deviations –Figure caption on a separate page