Experiments

Question 1

whats the aim of controlled experiments

Answer 1

isolate a variable (which is diagnostic of a hypothesis) that we are interested in.

Question 2

hall’s principle 1

Answer 2

dont experiment when we can find information through observation

Question 3

hall’s principle 2

Answer 3

no experiment should be performed without a distinct and definiate objective

Question 4

hall’s principle 3

Answer 4

dont needlessly repeat experiments

Question 5

hall’s principles 4 and 5

Answer 5

must efficient and responsibilty to desgin and execute and report efficient experiments

Question 6

hall’s principle 6

Answer 6

results be laid before the public in simplest and plainest terms

Question 7

define an experimental unit

Answer 7

a subject or group of subjects upon which an observation can be made

Question 8

when is an experimental unit required

Answer 8

both observational and experimental study

Question 9

why does an experimental unit need to be independent

Answer 9

systematic difference between units will confound the experiment

Question 10

blocking

Answer 10

the distribution of replicates in experiments to minimize any systematic difference between samples

Question 11

randomisation

Answer 11

esures the sample is representative of a population
ensures equal chance of a unit being placed in each group

Question 12

controls

Answer 12

comparison group
can be positive or negative

Question 13

How effective is this treatment? will require what type of control

Answer 13

negative

Question 14

is this treatment more effective? will require what type of control

Answer 14

postive

Question 15

statistical power of 0.95

Answer 15

we should detect an effect in 19/20 experiments.

Question 16

type II errors and statisical power

Answer 16

type II errors are directly related to statisical power
5% type II error rate is the standard in biology

Question 17

nominal data

Answer 17

mutually exclusive classes
male/female

Question 18

ordinal data

Answer 18

ordered categories
race order 1st/2nd/3rd

Question 19

strategies to increase effect size

Answer 19

choose best measurment
larger stimulus
use more sensitive subjects

Question 20

strategies to decrease variabiliy

Answer 20

improve uniformity of subjects or procedures
standardize the measured variable
improve experimental design

Question 21

how to present data

Answer 21

Aim is to convey information as clearly as possible.

Interpretation and commentary describing results should be clearly separated (often supported by report format).

Eg. Legends/Titles should describe content but avoid interpretation.

Methods cross referenced to results.

Question 22

presentation of raw data

Answer 22

It is good practise to plot out raw data as we have seen in earlier lectures.

We may well use statistical parameters to analyse & summarize these data but we need to show that they are truly representative.

Question 23

Representation of precision

Answer 23

Use a logical unit and number of significant figures when reporting numerical data.

Error bars! Think about what’s appropriate (e.g. variability vs. precision) and report what was used– see earlier presentation

Imperative to describe precisely how these were derived from the raw data.

Question 24

for genuine replication which three criteria must be satisfied

Answer 24

experimental units must be randomly and independently assigned to treatment groups.

The treatment(s) should be applied independently to each experimental unit. Injecting animals with a drug is an independent application of a treatment, whereas putting the drug in the drinking water shared by all animals in a cage is not.

The experimental units should not influence each other, especially on the measured outcome variables.