Quantitative data are data represented numerically, including anything that can be counted, measured, or given a numerical value. Quantitative data can be classified in different ways, including categorical data that contain categories or groups (like countries), discrete data that can be counted in whole numbers (like the number of students in a class), and continuous data that is a value in a range (like height or temperature). Quantitative data are typically analyzed with statistics.
(From the Data Glossary, National Center for Data Services, National Library of Medicine)
Quantitative Research Methods in Translation and Interpreting Studies by 
Quantitative Research Methodology in the Health Sciences by 
Quantitative Research Methods for Professionals in Education and Other Fields by 
Analyzing Quantitative Data by 
Quantitative and Statistical Research Methods by 
Research Design by 
Research Design by Interpretations related to mixed (sometimes called merged) methods vary; be wary of jargon! Gery Ryan, of the Kaiser Permanente School of Medicine, gives these definitions, while arguing that we should be thinking of the purposes of the research rather than the methodological labels:
Mixed methods research: “Combines elements of qualitative and quantitative research approaches (e. g., use of qualitative and quantitative viewpoints, data collection, analysis, inference techniques) for the broad purposes of breadth and depth of understanding and corroboration.”
Multimethod research: “Either solely combine multiple qualitative approaches or solely combine multiple quantitative approaches.”
Data triangulation: “Uses multiple sources of data or multiple approaches to analyzing data to enhance the credibility of a research study.”
(From "Mixed Methods Research Designs and Data Triangulation" by Gery Ryan, Kaiser Permanente School of Medicine)
Data Analysis Software:
Survey Data Collection Software:
(Descriptions from Wikipedia, except where noted)
Resources:
Library Data Services Program Referral Guide
Training:
Library Event Calendar (search "data' or other keywords)
Research Data Management events and training page
Python Bites: mini-tutorials from the Dartmouth University Library