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Chemistry > RIP final > Flashcards

RIP final Flashcards

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1
Q

How to proceed with answering the question: Is there a difference between the mean resting heart rate of men and women?

A

The first step is calculating the difference between the two means. We must transform this distance into a relative distance (t-statistic). It allows us to compare the difference to a standardized distribution (the t-distribution). We calculate the test statistic using the formula for t. When we have the value of t, we use p-value to measure how extreme the difference is.

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2
Q

What is the formula for the t-statistic?

A

observed difference/standard error for the difference in the two means

(M1 - M2) / SE(M1 - M2)

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3
Q

Once we have the value of t, what do we use to measure how extreme the difference is?

A

p-value

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4
Q

conditions of causality

A
  1. covariance
  2. temporal precedence
  3. internal validity
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5
Q

internal validity

A

Alternative explanations for the relationship should be ruled out

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6
Q

randomized experiment

A

A research design where:
▪by randomization, groups can be assumed to be similar
▪one variable is manipulated(varied) by the researcher
▪the researcher measures the effect of this manipulation on another variable (the outcome)

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7
Q

confounding variable

A

A second variable that happens to vary systematicallyalong with the intended independent variable. This variable is therefore an alternative explanation for the results

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8
Q

internal validity

A

asks if groups were comparable at the beginning of the experiment, with respect to the dependent variable and other dependent variables (observed and unobserved). If, for some reason, the groups turn out to be not comparable at the start of the experiment, we speak of a selection effect

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9
Q

selection effect

A

Crucial question: how were the groups created. To reduce selection effects, groups must be formed using random assignment. for some reason, the groups turn out to be not comparable at the start of the experiment, we speak of selection effect.

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10
Q

goal of random assignment

A

making sure that: the mean and variance in scores, on all variables, measured and unmeasured, are similar for both groups at the onset of the study

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11
Q

randomization issues

A

contamination

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12
Q

contamination in randomization

A

▪Participants in the experimental group communicate with participants in the control group
▪Participants do not adhere to the treatment
▪Influence from researcher(s)

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13
Q

PICO

A

The identifier of an experimental research question

Population
Intervention
Comparison
Outcome

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14
Q

what do researchers use when comparing mean scores of two independent groups?

A

independent sample t test

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15
Q

standard error for difference in means

A

contains the group sizes (n1and n2) and spread in scores in both groups (SD1and SD2)

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16
Q

With the t-test we consider the relative difference between the groups, using:

A

*The mean difference: M1–M2
*The spread in scores in both groups:SD1and SD2
*The group sizes: n1 and n2

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17
Q

the idea behind the test statistic t

A

When a lot of samples are drawn from a population in which H0is true, The difference between the sample means will often be near zero. So, t will often be near zero, too. Values of t that are far from zero will be found less often.

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18
Q

what is the standard error of t dependent on?

A

Group sizes (n1and n2) *Variation in scores in both groups (SD1and SD2)

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19
Q

as standard deviation increases, standard error

A

also increases

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20
Q

as n increases, standard error

A

decreases

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21
Q

overall the test statistic is dependent on

A
  • relative difference in means
  • standard deviation pooled (weighted average of sd in sample 1 and sd in sample 2)
  • and sample size per group
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22
Q

a larger diference in means what for the t value

A

larger t

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23
Q

more variation in scores means what for the t value

A

smaller t

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24
Q

larger samples means what for the t value

A

larger tr

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25
Q

randomization

A
  • key of true experiment
  • observed and unobserved factors are equally likely in both groups
  • transparent, reproducible
  • allows causal claims
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26
Q

between subject design

A

When participants are divided into different groups and each groups receives different treatment. The data is then compared between groups

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27
Q

within subject design

A

When all participants receive all different treatments (one after the other, possibly randomized in order). We first compare the data within each person

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28
Q

how does a pretest-posttest design compare to

A

can serve as a randomization check, correction for differences, and can track changes. in just a posttest design, we would not know if/how the groups differed at the beginning.

29
Q

disadvantage of the pretest-posttest design

A

learning effect

30
Q

solomon four group design and advantages/disadvantages

A

both prettest-posttest and just posttest. can solve unequal groups at the beginning and check for learning effect. however, can be highly costly.

31
Q

repeated measures design

A

where the same participants are measured multiple times under different conditions or at different time points. This allows researchers to examine changes within individuals, reducing variability and the need for a large sample size.

32
Q

counterbalanced measures design

A

A research design used to control for order effects in repeated measures studies. Participants experience all conditions, but the order of conditions is varied across participants to prevent biases from practice, fatigue, or carryover effects.

33
Q

quasi-experiment

A

Research designs that evaluate the effect of an intervention or treatment without random assignment. Instead, groups are naturally formed or pre-existing, making them useful in real-world settings where randomization isn’t feasible.

34
Q

interrupted time series design

A

A quasi-experimental design that measures an outcome variable repeatedly over time, both before and after an intervention or event (the “interruption”). It evaluates changes in trends or levels caused by the intervention, making it useful for analyzing the effects of policies, treatments, or external events.

35
Q

field experiment

A

An experiment with a close simulation of the conditions under which the process under study occurs or in a natural settin

36
Q

threats to internal validity

A

design confounds
selection effect

37
Q

design confounds

A

A second variable that happens to vary SYSTEMATICALLY along with the intended independent variable
▪This variable is therefore an alternative explanation for the results

38
Q

threats to internal validity in experimental design

A

▪Design confounds
▪Selection effect
▪Contamination
▪Learning effect
▪Maturation
▪History
▪Regressing to the mean
▪Attrition
▪Testing
▪Instrumentation

39
Q

threats to internal validity in all research

A

▪Observer bias
▪Demand characteristics
▪Placebo effect

40
Q

Observer bias

A

When the researcher has certain expectations and is influenced by this in assessing the participants/ interpreting the result

41
Q

Deman characteristics

A

When the participants realize what the study is for and therefore start to behave differently (in the expected direction

42
Q

Placebo effect

A

When participants make progress because they believe they are receiving an effective treatment

43
Q

Maturation

A

Is it the manipulation or the development (aging, maturing) that caused the differences?

Observed differences between the pre- and post-measurement could arise from natural developments of the participants, when participants’ characteristics change as part of a natural process.

44
Q

History threats

A

Is it the manipulation or external events causing the differences?

Not only natural changes of participants are a source of influence, but external events as well - events that are not necessarily related to the study.

45
Q

Regressing threats

A

Is it the manipulation or the natural “shifting” that caused the differences?

Regressing to the mean can occur when the participants show extreme values (on average) at the start of the experiment. At a later time, values are expected to be shifted towards the ‘normal’, less extreme, mean value.

46
Q

Attrition threats

A

Is it the manipulation or the drop-out of a group of participants that caused the differences?

When participants drop out during a study, the outcome can be affected by this. This is primarily a problem when the people that quit the study are different from the people that do not.

47
Q

Instrumentation threats

A

Is it the manipulation or the new instrument that caused the differences?

When the instrument measuring the dependent variable changes during the experiment, the results are affected.

48
Q

What are posible explanations if no effect is found after an experiment

A

weak manipulations

power problem (there is an effect, but too few participants to detect it)

no effect (there really is no difference in the population

49
Q

how is the null hypothesis protected in NHST?

A

by making the chance of making a type one error small (the significance level)

50
Q

chance of inverse of a type 1 error

A

power: 1-B

51
Q

power

A

chance of correctly rejecting H0. measures the chance that an existing difference in the population will be found by the sample data and the statistical test`

52
Q

what happens to power when alpha increases?

A

power also increases. By increasing alpha (the threshold for rejecting the null hypothesis), it becomes easier to detect a true effect, which increases the likelihood of rejecting the null hypothesis correctly, thereby increasing power. However, the chance of making a type 1 error also increases. Researchers need to find a balance between a small value of aand high power

53
Q

factors power is influenced by

A

The sample size

The size of the difference in the population

The level of significance

The spread (or variability) in the measured scores

The choice of the statistical technique

54
Q

type two error

A

A type II error is that the null hypothesis is not rejected, while the null hypothesis is not true.

55
Q

when spread in scores decreases, what happens to power?

A

power increases

56
Q

4 principles which are the basis of integrity in research

A

Reliability, honesty, respect, accountability

57
Q

major violations of scientific integrity

A

fabrication - making up data, deliberate

plagiarism - copying other people’s work, deliberate

data falsification - not reporting certain findings, adjusting data, misinterpreting it, all deliberately

58
Q

publication bias

A

absence of non-significant effects leads to bias towards large effects

59
Q

Causes of questionable research practices (QRP)

A

Scientific journals would like to publish interesting/innovative results, which attracts more readers AND researchers need to publish enough to make a career

60
Q

p-hacking

A

things like:
*Removing outliers to make a difference significant
*Add a few more participants to make results significant
*Run a different analysis than planned

61
Q

HARKing

A

hypothesising after results are known: in hindsight, formulating hypotheses and pretending that they were the main focus of the research all alon

62
Q

Solutions to questionable research practices

A

post-publication peer review

retraction

pre-registration of aims and intended methods and expectations

replication as a standard part of research

63
Q

Cohen’s D

A

Used to describe the size of a difference

Measure of relevance; expresses difference between two means in the number of standard devaitions

(M2-M1)/SDpooled

64
Q

SD pooled

A

Weighted average of SD1 and SD2

65
Q

confidence interval

A

another way to describe the size of the difference between the two groups. a range of plausible probable values based on sample data

66
Q

width of confidence interval depends on

A
  • Sample size (smaller standard error –> narrower interval)
  • Spread/variation in scores in population (means greater spread of scores in sample, so more uncertainty –> wider interval)
  • Chosen confidence level (95% confidence level widely used - more certainty, wider interval)
67
Q

Four parts to evaluate statistical validity

A
  1. significance is determined based on test statistic t and the p-value
  2. relevance is assessed using a measure of effect size, such as cohen’s d
  3. accuracy is assessed using a confidence interval
  4. suitability of statistical test is assessed by checking the assumptions
68
Q

how is effect size measured for regression analysis

A

R squared

69
Q

how is effect size measured for chi squared

A

Cramer’s V

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