Reasoning in Psychology Using Statistics Psychology 138 Spring 2015

Reasoning in Psychology Using Statistics Annoucements Exam 1 on Wednesday –In lecture: closed book, scantron –In labs: open book, open notes

Reasoning in Psychology Using Statistics Sample Population Inferential statistics to generalize back Sampling to make data collection manageable Sampling

Reasoning in Psychology Using Statistics Inferential statistics Where does “probability” fit in? Possible Samples Population Randomness in sampling leads to variability in sampling error “Randomness” in short run is unpredictable but in long run is predictable Allows predictions about likelihood of getting particular samples Examples: Odds in games of chance Lots of samples n=5

Reasoning in Psychology Using Statistics Odds in Poker What are the odds of being dealt a “Royal Flush”? Total number of possible outcomes Total number of outcomes classified as A Prob. of A = p(A) = 2,598,960 4 p(Royal Flush) = = ~1.5 hands out of every million hands

Reasoning in Psychology Using Statistics Odds in Poker What are the odds of being dealt a “Straight Flush”? Total number of possible outcomes Total number of outcomes classified as A Prob. of A = p(A) = 2,598, p(straightflush) = = ~15 hands out of every million hands

Reasoning in Psychology Using Statistics Odds in Poker What are the odds of being dealt a …? Total number of possible outcomes Total number of outcomes classified as A Prob. of A = p(A) =

Reasoning in Psychology Using Statistics Basics of probability: Derived from games with all outcomes known Draw lettered tiles from bag –Bag contains: A’s B’s and C’s. Both upper and lower case letters Total number of possible outcomes Total number of outcomes classified as A Prob. of A = p(A) = A a b B c C What’s the probability of getting an A (upper or lower case)? Sample space = 2/6 = 0.33

Reasoning in Psychology Using Statistics Basics of probability Prob. of A = p(A) = 2/6 = 0.33 First Pick: a A 1/6 2/6 + Second Pick: ? – it depends on how you sample Sampling with replacementSampling without replacement 2/6 1/5 The probabilities of selecting the titles change from 1 st to 2 nd pick A a b B c C a b B c C A b B c C A a b B c C What’s the probability of getting an A (upper or lower case) on the first pick and another on a second pick?

Reasoning in Psychology Using Statistics Basics of probability A a b B c C What’s the probability of getting an A (upper or lower case) on the first pick and another on a second pick? a A Sampling with replacement (2/6)*(2/6) = st pick2 nd pick b B c C 1 st picks2 nd picks a A bBcC a A bBcC a A bBcC a A bBcC a A bBcC a A bBcC 36 total outcomes 4/36 = outcomes of 2 A’s Sampling without replacement (2/6)*(1/5) = st pick2 nd pick a A b B c C A bBcC abBcC a A BcC a A bcC a A bBC a A bBc 30 total outcomes 2 outcomes of 2 A’s 2/30 = st picks2 nd picks

Reasoning in Psychology Using Statistics Basics of probability Most statistical procedures assume sampling with replacement For large populations it turns out not to matter much e.g., suppose your population is N=1,000,000. Starting probability of selecting a particular item 1 in 1,000,000. Sampling with replacement, odds stay at 1 in 1,000,000 Sampling without replacement, odds change to 1 in 999,999 the change is so small that it may not matter In experiments, you typically don’t want to use sampling with replacement because of the potential for lasting effects of your independent variable

Reasoning in Psychology Using Statistics Reviewing Producing Data Scientific method Research methods –Observation methods –Experimental methods –Quasi-experimental Variables –Types –Operational definitions Sampling –Samples and populations –Statistics and parameters –Techniques Measurements –Continuous and discrete –Scales of measurement –Instrument Errors in Measurement –Validity & Reliability –Confounds –Bias Reliability Experimental control Basic probability

Reasoning in Psychology Using Statistics In the news People who own dogs appear to get more exercise than those who do not … The researchers used a questionnaire to interview a random sample of 351 people ages 20 to 80 in the Vancouver, British Columbia, area, asking about their dog ownership and level of physical activity. Dog owners walked almost twice as many minutes per week as people who did not own dogs, and the dog owners spent more time in all forms of mild and moderate physical activity. Neither the sex of the owner nor the size of the dog made a difference: men and women who owned dogs participated in increased amounts of moderate exercise compared with those who had no dog. But no statistically significant difference between the two groups was evident in the amount of strenuous exercise performed. The authors concede that the study, published in the February issue of The American Journal of Preventive Medicine, does not determine whether owning a dog itself makes people exercise more. Shane Brown, the study's lead author and a graduate student at the Behavioral Medicine Laboratory of the University of Victoria, called this "the million-dollar question." When the researchers subtracted the time spent walking the dog from total physical activity, dog owners actually walked less than their counterparts without dogs. This, the researchers say, may suggest that the dog makes the difference. When dog owners choose to engage in moderate physical exercise, the reason may be that a four-legged member of the household is insisting on a walk. Now. Report (NY Times 2006): dog a more reliable exercise partner than a human.NY Times 2006

Reasoning in Psychology Using Statistics In the research literature Background Dog ownership may be an effective tailored intervention among adults for promoting physical activity. This study examined the relationship between walking, physical activity levels, and potential psychological mediators between people who owned dogs and those who did not own dogs in the Capital Region District of Greater Victoria, British Columbia, Canada. Data were collected in September 2004; analyses were conducted in January Methods A random sample of men (n=177) and women (n=174) aged 20 to 80 years participated. Questionnaires were mailed out in 2004 to collect information about demographics, dog ownership, leisure-time walking, physical activity levels, and theory of planned behavior (TPB) constructs. theory of planned behavior Results The analyses revealed that dog owners spent more time in mild and moderate physical activities and walked an average of 300 minutes per week compared to non–dog owners who walked an average of 168 minutes per week. A mediator analysis suggests that dog obligation acts as a mediator between dog ownership and physical activity. Moreover, the theory of planned behavior constructs of intention and perceived behavioral control explained 13% of the variance in walking behavior with an additional 11% variance in walking behavior being explained by dog obligation. Regarding intention to walk, the TPB explained 46% of the variance in intention to walk with dog obligation adding an additional 1% variance. Conclusions In this group of Canadians, those who owned a dog participated in more mild to moderate physical activity than those who did not. Acquiring a dog should be explored as an intervention to get people more physically active. Shane G. Brown, Bed. and Ryan E. Rhodes PhD School of Physical Education, University of Victoria, Victoria, British Columbia, Canada Available online 2 February American Journal of Preventive Medicineonline

Reasoning in Psychology Using Statistics In the news Regimens: Pounding the Pavement, Stopping at Fire Hydrants Research process –Ask research question –Identify variables & formulate hypothesis –Define population –Select research methodology –Collect data from a sample –Analyze data –Draw conclusions based on data –Repeat People who own dogs appear to get more exercise than those who do not …

Reasoning in Psychology Using Statistics In the news Regimens: Pounding the Pavement, Stopping at Fire Hydrants Research process –Ask research question –Identify variables & formulate hypothesis –Define population –Select research methodology –Collect data from a sample –Analyze data –Draw conclusions based on data –Repeat Context for our numbers People who own dogs appear to get more exercise than those who do not …

Reasoning in Psychology Using Statistics In the news Regimens: Pounding the Pavement, Stopping at Fire Hydrants People who own dogs appear to get more exercise than those who do not … Research process –Ask research question –Identify variables & formulate hypothesis –Define population –Select research methodology –Collect data from a sample –Analyze data –Draw conclusions based on data –Repeat

Reasoning in Psychology Using Statistics In the news Regimens: Pounding the Pavement, Stopping at Fire Hydrants Research process –Ask research question –Identify variables & formulate hypothesis –Define your population –Select a research methodology –Collect your data from a sample –Analyze your data –Draw conclusions based on your data –Repeat Variables –Independent (explanatory) variables –Dependent (response) variable –Control variables –Random variables –Confound variables Variables –Independent (explanatory) variables –Dependent (response) variable –Control variables –Random variables –Confound variables The researchers …, asking about their dog ownership and level of physical activity. Methods …. Questionnaires were mailed out in 2004 to collect information about demographics, dog ownership, leisure-time walking, physical activity levels, and theory of planned behavior (TPB) constructs. Variables –Operational level –Conceptual level Variables –Operational level –Conceptual level

Reasoning in Psychology Using Statistics In the news Regimens: Pounding the Pavement, Stopping at Fire Hydrants Research process –Ask research question –Identify variables & formulate hypothesis –Define your population –Select a research methodology –Collect your data from a sample –Analyze your data –Draw conclusions based on data –Repeat Scales of measurement –Nominal –Ordinal –Interval –Ratio Scales of measurement –Nominal –Ordinal –Interval –Ratio The researchers …, asking about their dog ownership and level of physical activity. - mild, strenuous Methods …. Questionnaires were mailed out in 2004 to collect information about demographics, dog ownership, leisure-time walking, physical activity levels, and theory of planned behavior (TPB) constructs. - men & women, own dog or not - time spent exercising Instrument used?

Reasoning in Psychology Using Statistics In the news Regimens: Pounding the Pavement, Stopping at Fire Hydrants Research process –Ask the research question –Identify variables & formulate hypothesis –Define population –Select research methodology –Collect data from sample –Analyze data –Draw conclusions based on data –Repeat The researchers used a questionnaire to interview a random sample of 351 people ages 20 to 80 in the Vancouver, British Columbia, area, (i.e., mailed out questionnaires) Was it simple random sampling? Stratified random sampling? Etc.? Was it simple random sampling? Stratified random sampling? Etc.? Is the sample representative? Is there bias in sample? Is the sample representative? Is there bias in sample?

Reasoning in Psychology Using Statistics In the news Regimens: Pounding the Pavement, Stopping at Fire Hydrants Research process –Ask research question –Identify variables & formulate hypothesis –Define population –Select research methodology –Collect data from sample –Analyze your data –Draw conclusions based on your data –Repeat The researchers used a questionnaire to interview a random sample of 351 people ages 20 to 80 in the Vancouver, British Columbia, area, Which Research Method?? –Observational study –Experimental methodology –Quasi-experimental methodology Which Research Method?? –Observational study –Experimental methodology –Quasi-experimental methodology Causal Claims?? The authors concede that the study… does not determine whether owning a dog itself makes people exercise more. This may suggest that.. when dog owners choose to engage in moderate physical exercise, the reason may be that [the dog] is insisting on a walk. Gather 2 pieces of data for each person: dog ownership, exercise

Reasoning in Psychology Using Statistics In the news Regimens: Pounding the Pavement, Stopping at Fire Hydrants Research process –Ask research question –Identify variables & formulate hypothesis –Define population –Select research methodology –Collect data from sample –Analyze your data –Draw conclusions based on your data –Repeat Possible confounds? Threats to internal validity? Possible confounds? Threats to internal validity? If follow-up experiment were designed, what would you do?

Reasoning in Psychology Using Statistics Reviewing Producing Data Scientific method Research methods –Observation methods –Experimental methods –Quasi-experimental Variables –Types –Operational definitions Sampling –Samples and populations –Statistics and parameters –Techniques Measurements –Continuous and discrete –Scales of measurement –Instrument Errors in Measurement –Validity & Reliability –Confounds –Bias Reliability Experimental control Basic probability