1. Scientific Method and Experimental Design

what is the process of the scientific cycle

observation

construction of a testable hypothesis

experimental design

gathering, recording and analysis of data

evaluation of results and conclusion

formation of a revised hypothesis

why is the scientific cycle used

refinement of ideas is normal, and scientific knowledge can be thought of as the current best explanation, which can be updated after evaluation of further experimental evidence

what is a null hypothesis

that there will be no statistically significant effect from varying the independant variable

when would a null hypothesis be valid

failing to find an effect while the experiment is well designed

how can conflicting data or conclusions be resolved

careful evaluation

further experimentation

how would a null hypothesis be rejected

if theres evidence for an effect, unlikely due to chance

when do scientific ideas become accepted

if theyre checked independantly and effects are reproducible

what are 4 ways an experiment is valid

validity

reliability

accuracy

precision

what is validity

variables controlled so that any measured effect is likely to be due to the independant variable

what is reliability

consistent values in repeats and independent replicates

what is accuracy

data, or means of data sets, are close to the true value

what is precision

measured values are close to each other

why are pilot studies used

help plan procedures, assess validity and check techniques

allows evaluation and modification of experimental design

ensure an appropriate range of values for the independent variable

what is an independant variable

the variable that is changed in a scientific experiment

what is a dependant variable

the variable being measured in a scientific experiment

what categories can variables be placed into

continuous

discrete

what do experiments involve in terms of independant variables

manipulation of the independent variable by the investigator

what is an experimental treatment group compared to

a control group

what is a simple experimental design

only contains 1 independant variable

what is a multifactorial experimental design

more than 1 independant variable or a combination of treatments

what is an advantage of simple experimentation compared to multifactorial

conducted more easily

what is a disadvantage of simple experimentation compared to multifactorial

simple experiment findings may not be applicable to a wider setting

what is an advantage of multifactorial experimentation compared to simple

potentially provides more informative and useful results than simple experiments

what is a disadvantage of multifactorial experimentation compared to simple

difficult to design and control

why would investigators use groups that already exist

so theres no truly independant variable

what are observational studies good for

detecting correlation

why are observational studies not useful for determining causation

they dont directly test a hypothesis

why are independant variables not directly controlled by investigators

ethical or logistal reasons

what are confounding variables

variables besides the independant variable that may affect the dependant variable due to the complexities of biological systems

how should confounding variables be dealt with

be held constant if possible

monitored so that their effect on the results can be accounted for in the analysis

how are confounding variables dealt with if theyre not easily controlled

use a randomised block to try remove the effect of the confounding variable

how are blocks used

to be distributed in such a way that the influence of the confounding variable is likely to be the same across all the groups and therefore doesnt affect results

what types of controls are there

negative

positive

what are negative controls

something that provides results in the absence of a treatment

what are positive controls

a treatment that is included to check that the system can detect a positive result when it occurs

what is a placebo

a treatment without the presence of the independent variable being investigated

what is the placebo effect

a measurable change in the dependent variable as a result of a patient’s expectations, rather than changes in the independent variable

what types of studies are there

in vivo

in vitro

what are in vitro studies

the technique of performing a given procedure in a controlled environment outside of a living organism

what are in vivo studies

experimentation using a whole, living organism

what are examples of in vitro experiments

cells growing in culture medium

proteins in solution

purified organelles

what are advantages of in vivo

provides data for effects in whole organisms

allows study of complex interactions

what are advantages of in vitro

simpler and less expensive

easier to control confounding variables

interpretation of results is simpler

can demonstrate correlation and causation

what are disadvantages of in vivo

expensive and time consuming

ethical and legislative concerns

difficullt to control confounding variables

results may be difficult to interpret

difficult to prove causation

what are disadvantages of in vitro

difficult to extend results to whole organisms or different species

difficult to model complex interactions or systems

when is a representative sample of a population used

where its impractical to measure every individual

how is an appropriate sample size determined

the extent of natural variation within a population

what does a more variable population mean in terms of sample size

a larger sample size is required

what should a representative sample have

should share the same mean and the same degree of variation about the mean as the population as a whole

what are the ways of sampling

random

systematic

stratified

what is random sampling

members of the population have an equal chance of being selected

what is systematic sampling

members of a population are selected at regular intervals

what is stratified sampling

the population is divided into categories that are then sampled proportionally

what could variation in experimental results be due to

reliability of measurement methods and/or inherent variation in the specimens

how is the reliability of measuring instruments or procedures determined and what does the variation mean

by repeating measurements of a individual datum point in which the variation indicates the precision of the instrument

how is the natural variation in biological material determined

measuring a sample of individuals from the population

what does the mean indicate

an indication of the true value being measured

what does the range indicate

the extent of variation in the results

what does a narrow range mean

the variation is low

what are the types of data

qualitative

quantitative

ranked

what is qualitative data

subjective

descriptive

deals with data that can be observed but not measured

results presented using bar charts or pre charts

what is quantitative data

objective

deals with data that can be measured

numerical

results presented using either graphs or histograms

what is ranked data

when numerical values are replaced by their rank when the data are sorted from lowest to highest

when does correlation exist

if theres a relationship between 2 variables

when does causation exist

if the changes in the values of the independant variable are known to cause changes to the value of the dependant variable

what is a positive correlation

when an increase in one variable is accompanied by an increase in the other variable

what is a negative correlation

when an increase in one variable is accompanied by a decrease in the other variable

what is the strength of correlation proportional to

the spread of values from the line of best fit