Session 2a

Question 1

what is a Hypothesis

Answer 1

Assumption/prediction made about a population parameter (NOT about a sample estimate)

Question 2

Ad campaign A is preferred to B
Getting $1 million will make people happier 6 months later
Drug A will increase survival rate of AIDS patients

these are example of what

Answer 2

hypotheses

Question 3

Traditionally, experimental research engages in a procedure for what

Answer 3

hypothesis testing (NHST)

Question 4

what is (NHST)

Answer 4

Null hypothesis signifiance testing

Question 5

is NHST used still

Answer 5

NHST is still widely used

More recent approaches focus on effect sizes and formation of confidence intervals

Question 6

what are the Steps for Hypothesis Testing

Answer 6

Step 1: Set Up a hypothesis
Step 2: Choose α (significance level)1
Step 3: Examine your data and compute the appropriate test statistic
Step 4: Make the decision whether to “reject” or “not reject” the null hypothesis

Alternatively, look at the signifiance level (p-value) for the test statistic value

Question 7

explain Step 1: Set Up a hypothesis

Answer 7

Usually a prediction that there is an effect of certain variable(s) in the
population Example:
Eating fries will give you high cholesterol

Null and Alternative Hypothesis

Question 8

what is null hypothesis

Answer 8

(H0)
This is what we test statistically
No effect (“People will have equal cholesterol regardless of how many fries they eat”)

Question 9

what is Alternative Hypothesis

Answer 9

(H1)
Research/experimental hypothesis
Some effect (“People eating more fries will have higher cholesterol than those who eat less fries”)
Sometimes Ha is used to denote the alternative hypothesis

Question 10

what is Step 2: Choose α (alpha) (significance level)1

Answer 10

Decide the area consisting of extreme scores which are unlikely to occur if the null hypothesis is true
Proportion of times we are willing to accidentally reject H0, even if H0 is true

Question 11

Conventionally, α = what

Answer 11

.05 or α = .01

Question 12

The cutoff sample score for α is called what

Answer 12

the critical value

Question 13

explain Step 4: Make the decision whether to “reject” or “not reject” the null hypothesis

Answer 13

Compare the calculated value of your test statistic to the critical value for α

Question 14

in step 4, If your value is greater than or equal to the critical value what happens

Answer 14

reject H0. Otherwise, retain H0

Question 15

a decision to reject H0 implies what

Answer 15

acceptance of H1

Question 16

explain Alternatively, look at the signifiance level (p-value) for the test statistic value:
Such values often given by SPSS, R, or other statistical software If p ≤ α (e.g., p ≤ .05), what do you do to the null

Answer 16

reject H0. Otherwise, retain H0

this is a yes/no decision

Question 17

If H0 is rejected, you may conclude what

Answer 17

that there is a statistically significant effect in the population

“Eating fries has a statistically significant effect on cholesterol levels”

Question 18

“statistically significant” effect does not indicate what

Answer 18

We have a precise estimate of the effect

The effect is important or meaningful

Question 19

explain how ‘stat sig’ does not indicate that We have a precise estimate of the effect

Answer 19

It may be that an effect is “significant”, but there is some error around our estimate
The amount of error is represented in the standard error for the estimate The effect may be smaller or larger than our estimate

Question 20

explain how ‘stat sig’ does not indicate The effect is important or meaningful

Answer 20

Suppose we find that eating 1kg fries/month leads to 10g weight gain Is 10g really a meaningful amount?
Weight gain may be “significant” if it was observed from many people

Question 21

what is a Confidence Interval

Answer 21

gives us information about the precision of our estimates

Example: a 95% confidence interval (CI) may indicate that true weight gain in the population is between 2g and 18g per month

We don’t know for sure that a 95% CI will contain the true value of the effect in the population
If we repeated our experiment many times, 95% of the time a 95% CI will contain the true effect

Question 22

for Confidence intervals, Usually, we form {(1 − α) × 100}% CIs meaning what

Answer 22

If α = .05, we form a 95% CI

If α = .01, we form a 99% CI

Question 23

for Confidence intervals, As sample size increases what happens to your estimate

Answer 23

our estimate becomes more precise

And our CI intervals may become smaller or more narrow

Question 24

As α decreases what happens to the CI

Answer 24

Our CI intervals become larger or wider

Question 25

how to Calculate an effect size

Answer 25

A standardized measure of the magnitude of a treatment effect Commonly used measures of effect size:
Pearson’s correlation coefficient (r) or correlation ratio squared (R2) Cohen’s d
Omega (ω) or omega squared (ω2)
Eta squared (η2)

Question 26

Effect sizes are useful for what

Answer 26

assessing the importance of our effects

Question 27

how to determine if an effect is small or large

Answer 27

r = .10 (small effect)
r = .30 (medium effect) 
r = .50 (large effect)

Question 28

what are the Two types of errors in hypothesis testing

Answer 28

Type I: Reject H0 when it is true (False Positive)

Type II: Retain H0 when it is false (False Negative)

Question 29

Hypothesis Testing About a Single Mean - z-test

what is the purpose

Answer 29

Based on the sample mean (X) we test whether the population mean
(μ) is equal to some hypothesized value

Question 30

Hypothesis Testing About a Single Mean - z-test, Prior Requirements/Assumptions:

Answer 30

The variable, X, in the population is normally distributed
The population standard deviation, σ, must be known
The sample must be a simple random sample of the population (independence of observations)

Question 31

Computing a z-test for a single mean is like calculating what

Answer 31

a Z-score for your sample mean

Question 32

look at snapshots to understand z (standard) scored

Answer 32

on desktop

Question 33

A distribution of standard scores have Mean = what

Answer 33

0

Question 34

A distribution of standard scores have Standard Dev of what

Answer 34

Standard Deviation (SD) = 1

Question 35

If μ and σ are used, we get a z-score for the individual relative to who

Answer 35

other people in the population

Question 36

If the distribution of scores follows a normal distribution, a Z-score transformation will transform all scores to what

Answer 36

a standard normal distribution

aka The shape of the distribution does NOT change, only the units

Question 37

explain X ∼ N(μ,σ^2) → Z ∼ N(0,1)

Answer 37

for z-score
“~” means “distributed as” or “follows. . . ” (some distribution)
“N” is notation for “Normal” with “(Mean,Variance)” in parentheses

Question 38

If scores are on standard normal distribution what can we do

Answer 38

more easily interpret them

Question 39

what is μ0

Answer 39

the value of μ under H0, sometimes called a test value

Question 40

what is σX -

Answer 40

is the standard deviation for the sampling distribution of X

Question 41

σX - is the standard deviation for the sampling distribution of X
Special name for this concept is what

Answer 41

standard error

Question 42

What is a sampling distribution?

Answer 42

Suppose we conduct our experiment a million times
Each time, we obtain a sample of N = 25 McGill Psyc 305 students and a different value for mean IQ: X
σX is the SD for the resulting sampling distribution:

Question 43

If α = .05 (two-tailed), then our critical value, zcrit,α/2, is about what

Answer 43

1.96

Question 44

If α = .05 (two-tailed), then our critical value, zcrit,α/2, is about 1.96
If H0 is true…

Answer 44

About α/2 = 2.5% of observed z-tests will be less than -1.96 About α/2 = 2.5% of observed z-tests will be greater than 1.96 2.5% + 2.5% = 5% (desired level for α)2

Question 45

Limitations of z-test

Answer 45

Knowing the true value of the population standard deviation (σ) is unrealistic
Except in cases in which the entire population is known

Question 46

what is the alternative to the z-tes

Answer 46

t-test