Presentation on theme: "Statistical Analysis I have all this data. Now what does it mean?"— Presentation transcript:
1 Statistical Analysis I have all this data. Now what does it mean?
2 Is your data Quantitative or Qualitative? Continuous quantitative – measurement scale divisible into partial unitsEx-Distance in kilometersDiscrete quantitative - measurement scale with whole integers onlyEx- number of wolves born in given yearQuantitative data can be subdivided into:Ratio - with equal divisible intervals & absolute zeroInterval - does not have absolute zeroQualitative Nominal - objects are named or can’t be rankedExample- Gender (male/female)Qualitative Ordinal - objects are placed into categories that can be rankedExample- activity of an animal on a scale of 1 to 5Decide which type of data you have__________________
3 Describing data Central tendency (How different 2 sets of Data is) Mode - value that occurs most oftenMedian - middle value when ranked highest to lowestMean - mathematical averageVariation (How spread out the data is)For quantitative data –RangeFor qualitative data -Frequency distribution Frequency Distribution example link
4 Statistics Software … is not going to do your job for you. It is: not going to tell you what test to selectnot going to tell you if the test you selected is the right onenot going to tell you how to interpret the test results.
5 Making decisions about descriptive statistics & Graphs Quantitative DataQualitativeParametersRatio dataInterval dataNominal dataOrdinal dataType of datadata collected using a scale with equal intervals and with an absolute zero (distance, velocity)using a scale with equal intervals but no absolute zero (temp0C, pH)objects are placed into categories that cannot be ranked (male/female or brown, black, red hair)objects are placed into categories that can be ranked (Moh’s hardness scale or color ranked 1- 10)Central tendencyMeanModeMedianVariationRangeStandard deviationVarianceFrequency DistributionDegrees of freedomTotal # of samples -2(ex = 28)(#rows –1) x (#columns-1)Level of significance0.0250.05Decide which type of data you have, parameters you will need to calculate and on your Excel chart, enter the formula for each of the parameters.
6 Inferential Statistics Is the data statistically significant? Statistical TestsThe t-test (or Analysis of Variance):two or more groupsto compare measurements of each group.The Chi-square test:counts that can be placed into yes or no categories, or categories such as quadrants.The Pearson R Correlation:to test how the values of one event or object relates to the values of another event or object
7 How to select statistical test How to select statistical test? Is Dependent Variable (DV) continuous, ordinal, or nominal?
10 Null Hypothesis (μ)…..states that there is no difference between the mean of your control group and the mean of your experimental group. Therefore any observed difference between the two sample means occurred by chance and is not significant.If you can reject your null hypothesis then there is a significant difference between your control and experimental groups. Hence accept the alternative (original hypothesis).Write your null hypothesis _____________________________
11 Probability - Chance Could the difference between the groups due to random chance /error? Probability of error or p-value < 0.05 means thatthe error in the research is 5/100 or below 0.05(95% results have no error)P<0.05Less than 5% chance is considered to be OK.Reject Null hypothesisAccept your alternative (original) hypothesisP>0.05Greater than 5% then the data is not significant.Must accept Null hypothesis
12 Level of significance () and Degree of freedom (df) Level of significance () - It communicates probability of error in rejecting Null hypothesisp-value < 0.05 means that the probability of error in the research is 5/100 (95% results with no error)Degree of freedom (df) - It is number of independent observations in a sample.t-test df = (n1-1) + (n2-1)Chi-square df = (#rows – 1) (#columns – 1)Pearson R correlation df = (n-2) subtract 2 from the number of comparisons made.T test Chi square tables.doc
13 Accept or Reject the null hypothesis Find the table value for the t-test and the Chi-square test(using calculated degrees of freedom and the Level of Significance of 0.05 = 95%)Compare calculated value to table value.Calculated value < table valueNull hypothesis is NOT rejectedCalculated value > or = table valueNull hypothesis is rejected.