fundamentals of scientific experiments

statistics

what does correlation tell us?

the correlational meaning of explanation (e.g. the coeficient of determination) and the correlational meaning of prediction (e.g. the regression coeficient)

what is the first criteria for causality?

the cause and the effect variables should covary

what is the second criteria for causality?

the causal variable should precede the effect variable (proofs, not theoretical/logical precedence)

what is the third criteria for causality?

the alternative causes should be excluded/controlled

what is the fourth criteria for causality?

there should be a logical connection between the causal and the effect variables

which of the four criteria of causality is met in correlation studies?

the cause and the effect variables covary

what is one important aspect of correlational studies?

are non-experimental, which means that the experimenter does not manipulate or control any of the variables

what does an experiment allow?

test causal relationships between variables/to establish causes of behavior

first essential property of experimental research?

manipulation of an independent variable to assess its effects on dependent variable/participant’s behavior

second essential property of experimental research?

the researcher must assign participants to various experimental conditions in a way that assures their initial equivalence (random assignment)

third essential property of experimental research?

the researcher must control extraneous/confunding variables that may influence participants‘ behavior

what is the independent variable?

the variable manipulated by the experimenter in a controlled manner

what are the 3 types of independent variables?

environmental manipulations, instructional manipulations and invasive manipulations

what is one important aspect regarding levels of independent variable?

the levels of the independent variable must be different enough to produce a detectable effect on behavior

what is a manipulation check?

question(s) /item(s) designed to determine if the independent variable was successfully manipulated

what is the dependent variable?

the variable that is supposed to change as an effect of the independent variable (the response measured in the study, the outcome)

dependent variables can be:

observations of the behavior, self reported measures, measures of physiological reactions

what is entire rationale of the experiment regarding assignment of participants?

the entire rationale of the experiment is based on the equivalence of the groups in the beginning of the study

what happens with the initial non-equivalence of the 2 groups ?

the initial non-equivalence of the experimental & control group will be confounded in the end with the effect of the manipulation

what are the 3 types of assignment?

single random assignment, matched random assignment and repeated measures design

out of the 3 types of assignment which one is indepedent samples?

simple random assignment

what does probabilistic reasons refer to in the case of simple random assignment?

random assignment relies on probability ,meaning that white it generally balances groups, there is always a chance of imbalance due to randomness-expecially in small samples, so it doesn’t guarantee equal sample sizes

in comparison to simple random assignment, matched random assignment….?

ensures that participants are balanced across conditions based on a relevant characteristic

define experimental control

eliminating or holding constant extraneous factors (confounding variables) that might affect the outcome of the study (the dependent variable)

what is total variance?

how much participants’ scores vary from one another

what is

between-groups variance, total differences between the experimental conditions

what is treatment variance?

differences between experimental conditions due to the manipulation of the independent variable

what is confound variance?

differences between experimental conditions due to confounding variables that differ systematically between experimental conditions

what is error variance?

within-groups variance; unsystematic differences between participants

the total variance equals to?

treatment variance+ confound variance + error variance

basically total variance equals to?

systematic variance (between) + unsystematic variance (within)

systematic variance is composed of?

treatment variance and confound variance

what are some sources of error variance?

1. differences of personal attributes among participants (e.g. personality, experience)

2. differences in the way the experimenter interacts with each participant

3. measurement error