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BYS 120 Lab Section 03 – Monday 1-3 pm Section 08 –Tuesday 9:40-11:40 am Jana Whittle [email protected] BYS 120 Lab 2 Scientific Investigation Image credit: http://www.sciencegeek.net/Chemistry/Presentations/Measuring/ The Scientific Method Image Credit: ArchonMagnus [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], from Wikimedia Commons Scientific Hypothesis Hypothesis • Explanatory statement specific to the research • Why should the research show a difference • Must be testable • Statistically testable or with further experiments • Must be falsifiable Predictions • Outcomes that should occur based on the hypothesis • Generally an if…then type of statement • If hypothesis or explanation then this outcome should be observed Null Hypothesis • Proposed for research that will be tested through statistical analysis • Proposes that any variance that is measured in the experiment is due to random chance and not the explanatory hypothesis Independent Variables Dependent Variable Control Variable Control Treatment A variable that is changed to observe a response A variable affected by the experiment A factor that is kept constant across all treatments A group that is not manipulated during the experiment A treatment applied to the subject of the experiment Measured or counted in the observational response Example: The temperature is kept constant for all mice Usually plotted on the x-axis Usually plotted on the y-axis Serves as comparison for the observations seen in the experimental subjects Example: Varying the amount of sugar in diet of mice Example: The weight gain/loss of each mouse Example: A group of mice that were fed a standard mouse diet Variable Types Statistical Measurements Image Credit: https://dzone.com/articles/introduction-to-basic-statistics-measurements Mean Measurements of Central Tendency Median Average of measured values Middle of the measured values Add all values and divide by number of observations Values must be ordered from lowest to highest Use when data is evenly spread out Determine the middle value If even number of values use average of 2 middle values Useful when data has outliers Mode The most frequently occurring value Useful when data is clustered out one or two values Measurements of Dispersion Range Standard Deviation Standard Error Span of the values Quantifies variability of the values Quantifies dispersion around the mean Widely scattered values indicate more variability in the data Indicates confidence of the mean Spread between largest and smallest values Find maximum value and subtract the minimum value Expressed in terms of the central measurement Eg: Variability around the meand Calculated using mean and standard deviation Error generally decreases as the number of samples increases Inferential Statistics Inferential Statistics determine if the hypothesis is supported Measure whether the observed values are an effect of the experiment or can be explained through random chance p-values are used to make this decision Range from 0 to 1 0 observation impossible due to chance 1 observation entirely due to chance < 0.05 is threshold for determining the observations were not due to chance alone – reject the null hypothesis Lab 2 Lab 2: Test a hypothesis of the human body Vitruvius proposed a ¼ rule of human proportions Middle of chest to top of leg Bottom of knee to bottom of foot Top of head to middle of chest Top of leg to bottom of knee He also proposed the arm span was equal to height Lab 2: Test Vitruvius proposal that human arm span and height are identical Lab 2: Lab Activity Write a explanatory hypothesis and prediction. Write a null hypothesis and prediction Sketch an image of how arm span and height will be measured Measure arm span – to nearest 0.1 cm Measure from tip of middle finger to tip of other middle finger Stretch arms wide apart and parallel to the floor Measure height - to nearest 0.1 cm Measure from top of head to the floor Stand barefoot, upright and against the wall Record the values for entire class in the table Lab 2: Assignment (10 points) Due in Canvas in 24 hours Lab 2: Lab Assignment Upload a Word file to Canvas that includes: Explanatory hypothesis and prediction Null hypothesis and prediction Follow lab manual instructions to: Calculate descriptive statistics and report them in a table – round to one decimal place and include units Generate a figure for your data – label axis with units and include a caption Draw a conclusion for your hypothesis by using a t-test and report the p-value