Selecting a statistic test
In the measures, we define and identify our outcomes or endpoints. We can identify one outcome or endpoint as our primary outcome and we can have several other secondary outcomes or endpoints
We will look at tests pertaining to quantitative research and focus on some of the basic or commonly used tests. We will not run a discussion of the theoretical background of statistical tests in this module.
You can use this module to identify some of the common tests that you can employ in your research (and based on your research design and question)
Note: Earlier, we mentioned the need to note down anticipated answers. Your research question and anticipated answers will help you plan the tests that will be useful for your research. Please be aware that your anticipated choice of test may change after you conduct your research based on the data you obtain.
STEP 1: IDENTIFY THE DEPENDENT VARIABLE OF INTEREST
STEP 2: IDENTIFY THE INDEPENDENT VARIABLE(S) OF INTEREST
Identify One Dependent Variable  
No Independent Variable  Univariate Analysis  Can be

One Independent Variable  Bivariate Analysis  Can be

More than one Independent Variable  Multivariate Analysis  Can be

Let us look at each of these scenarios
Univariate Analysis
Assumptions
 Population from which sample is drawn is normally distributed
 Sample (s) are randomly selected from the population
 Samples have approximately equal variance (homogeneity of variance)
 Parametric data based on an interval or ratio based scale
Continuous Dependent Variable & No Independent Variable  Comparing Means  Students ttest 
Continuous Dependent Variable & No independent Variable  comparing one preand one post measure in same subject  Paired t test 
Assumptions
 Distribution free or nonparametric data
 Samples are randomly selected or representative of a general population
Ordinal Dependent Variable & No independent Variable  Comparing Medians  Wilcoxon Sign Rank test 
Nominal Dependent Variable Affected by Time & no independent variable  Rate  Normal Approximation to Poisson 
Nominal Dependent Variable NOT affected by time– Outcome Common & No independent Variable  Proportion  Normal Approximation to Binomial 
Nominal Dependent Variable NOT affected by time– Outcome Uncommon & No independent Variable  Proportion  Normal Approximation to Poisson 
Bivariate Analysis
Ordinal Dependent Variable & No independent Variable  Comparing Medians  Wilcoxon Sign Rank test 
Nominal Dependent Variable Affected by Time & no independent variable  Rate  Normal Approximation to Poisson 
Nominal Dependent Variable NOT affected by time Outcome Common & No independent Variable  Proportion  Normal Approximation to Binomial 
Nominal Dependent Variable NOT affected by time Outcome Uncommon & No independent Variable  Proportion  Normal Approximation to Poisson 
Ordinal Dependent Variable & No independent Variable  Comparing Medians  Wilcoxon Sign Rank test 
Nominal Dependent Variable Affected by Time & no independent variable  Rate  Normal Approximation to Poisson 
Nominal Dependent Variable NOT affected by time Outcome Common & No independent Variable  Proportion  Normal Approximation to Binomial 
Nominal Dependent Variable NOT affected by time Outcome Uncommon & No independent Variable  Proportion  Normal Approximation to Poisson 
Continuous Dependent Variable & Continuous Independent variable from naturalistic or purposive sampling  Slope and Intercept  Regression Analysis, FTest 
Continuous Dependent Variable & Continuous Independent Variable from naturalistic sample  Pearson’s correlation coefficient  Correlation analysis, Students ttest 
Continuous Dependent Variable & Nominal Independent Variable from naturalistic sample or purposive sample  Difference between means  Students ttest 
Ordinal Dependent Variable & Ordinal Independent Variable from naturalistic sample  Spearmans Correlation Coefficient  Spearmans Correlation test 
Ordinal Dependent Variable & Nominal Independent Variable from a naturalistic or purposive sample  Difference between medians  Mann Whitney Test 
Nominal dependent Variable NOT AFFECTED by time & Nominal Independent Variable paired design  Odds Ratio, Relative Risk, difference in proportions  McNemars test 
Nominal dependent Variable NOT AFFECTED by time & Nominal Independent Variable unpaired design  Odds Ratio, Relative Risk, difference in proportions  Chisquare test, normal approximation, Mantel Haenzel Test, Fishers Exact Test 
Nominal dependent Variable AFFECTED by time & Nominal Independent Variable unpaired design  Rate difference or ratio  Normal approximation 
Nominal dependent Variable NOT AFFECTED by time & Continuous Independent Variable  Slope and intercept  Chisquare test for trend 
Multivariate Analysis
Continuous Dependent Variable & Nominal Independent variables representing one characteristic  Means  OneWay Analysis of Variance (ANOVA), F test, Student Newman Keuls Test 
Continuous Dependent Variable & Nominal Independent variables representing > 1 characteristic  Means  Factorial Analysis of Variance (ANOVA), F test, Student Newman Keuls Test 
Continuous Dependent Variable & Continuous Independent Variables from naturalistic sample or purposive sample  Regression coefficients  Multiple regression analysis, F test, partial F test 
Continuous Dependent Variable & Continuous Independent Variables from naturalistic sample  Coefficient of determination  Multiple correlation analysis, F test 
Continuous Dependent Variable & Nominal or continuous Independent Variables from a naturalistic or purposive sample  Regression coefficients  Analysis of Covariance (ANCOVA), F test, Partial F test 
Ordinal Dependent Variable & Ordinal Independent Variables  Kendalls coefficient of concordance  Chisquare test 
Ordinal Dependent Variable & Nominal Independent Variables  Mean of Ranks  Kruksal Wallis Test or Dunn’s test 
Nominal dependent Variable AFFECTED by time & Continuous and Nominal Independent Variables  Incidence Ratio  Cox Proportional Hazards Regression, Chisquare test 
Nominal dependent Variable NOT AFFECTED by time & Continuous and Nominal Independent Variables  Odds Ratio  Logistic Regression, chi square test 
Nominal dependent Variable AFFECTED by time & Nominal independent Variables  Cumulative probabilities  Kaplan Meier Life table analysis, Mantel Haenzel Test or logrank test 
Nominal dependent Variable NOT AFFECTED by time & Nominal independent Variables 
Odds ratio, relative risk or difference in proportions 
Stratified analysis, Mantel Haenzel test 
In subsequent posts, we will look at how to do each of these tests and interpret them, using real life data examples.
Post attributed to Research Action Group AMMA ERF