Transcript Lecture 25
Research Methodology Lecture No :25 (Hypothesis Testing – Difference in Groups) Recap • Goodness of data is measured by reliability and validity. • Three measures of central tendency: mean, median and mode. • Dispersion is the variability. • Three measures of dispersion are: range, variance and standard deviation. • Correlation • SPSS Cronbach Alpha (Reliability) Factor Analysis (Validity) Hypotheses Testing • Difference between groups • Relationship between variables Types of Hypotheses Null •that no statistically significant difference exists between the groups •No Statistically significant relationship exists between variables Alternative •logical opposite of the null hypothesis •that a statistically significant difference does exist between groups •That statistically significant relationship exists Choose Appropriate Tests • Based on the number of variables i.e. two variables relationship (Univariate)and many variables (Multivariate) statistical techniques. • The type of scales Nominal, Ordinal(Non Metric) , Interval and Ratio(Metric) used choose appropriate tests • See page 338 of the text book. Computer Outputs • See the output results of the computer generated outputs indicating the significance level. Testing for Statistical Significance •State the null hypothesis •Choose the statistical test •Select the desired level of significance •Compute the calculated difference value •Obtain the critical value •Usually the software now provides the standard significance values and the f or t values. Based on the significance level value one can interpret the test •Interpret the test Selected Group Difference Cases • Group difference – Testing single mean – Testing two related means (ratio) – Testing two related samples when data is in ordinal / nominal – Testing two in unrelated means – Testing when more than two groups on their mean scores Testing a hypothesis about a single mean • One sample t test • Mean of the population from which a sample is drawn is equal to comparison standard. • i.e. we known that the in general the students on an average study for 32 hours. • Now you want to test that the students at VCIIT which are part of the student population study less. • So the sample of V-CIIT differ from the rest of the population needs to be tested. • Hypothesis generated would be • Ho: The number of study hours of students V_CIIT is equal to the number of hours studied in general.(same)(no difference) • Ha: The number of hours students of V_CIIT is less then the number of hours studied in general (< ) • • • • SPSS Analysis Compare means One sample T Test. Say you set the significance level to 0.05 then See the output results of generated from the software. See if the differences are significant or the relationship significant. (lecture 6-7) • If the differences are not significant then we accept the null hypotheses other wise accept the alternate • Out Put (T value and significance level) Testing hypotheses about two related means • Paired samples t-test • Examine the difference in the same group before and after the treatment • Performance before training and after training • Two observation each employee • Null hypothesis – There is no difference between the performance of before and after the training • SPSS • use pair t test and see the value of t and it’s significance level • If the differences are not significant then we accept the null hypotheses other wise accept the alternate • Meaning the before and after training there was no change i.e. Null hypothesis is accepted – There is no difference between the performance of before and after the training Non Parametric Test for paired sampled • When population cannot be assumed to be normally be assumed distributed • Use Wilcoxon singed –rank test , • Use McNemar’s test for non parametric and nominal data Testing about two unrelated means • Group difference when groups are not related and variable of interest data is in interval and ratio scales. • E.g: Groups MBA and Non MBA compared on sales achieved. • SPSS Analyze Compare means Independent samples T Test • If more than two groups use ANOVA ( sales by different level of education(Metric, FA, BA/BS,Masters ) • SPSS excercises