Institute
Consulting

Consulting service at the institute

The Biostatistics section offers statistical consulting for students and staff of the Faculty of Natural Sciences.

STATISTICAL CONSULTING

Germination data in : R. Mead, R.N. Curnow, and A.M. Hasted. Statistical methods in agriculture and experimental biology. CRC Press, 2002.

What we do:

  • discuss your experimental design and questions of interest and recommend adequate statistical methods
  • provide exemplary evaluation of your data using R
  • describe and explain the applied statistical methods, provide example interpretation of the results, and references for the applied methods

What we don't do:

  • provide consultancy without having arranged a date via e-mail before
  • evaluate all datasets you have, especially if the method of analysis is the same for each dataset
  • fix problems in Excel, SigmaPlot, Minitab, Matlab, Stata, SPSS, Statistica, …

    Contact

    In order to make your consultation as effective as possible we ask you to provide some information by email beforehand:

    • name, e-mail, phone number, institute
    • a precise description of your experiment:
      • What is the motivation/goal of your experiment?
      • What was your experimental design (experimental units, randomization, replication…)?
      • What are response variables and what are explanatory variables (treatment factors, covariates)?
      • What are the questions/hypotheses of main interest?
      • Are there further questions/hypotheses of interest?
    • your dataset (if possible):
      • attached as one of the usual file types (txt, csv, …)
      • in flat file format (i.e., each row contains one single observation, and variables are listed column by column; exeptions are possible, e.g. for highdimensional data)

    Please write an e-mail containing the above information to consulting@cell.uni-hannover.de. We will then get back to you soon.

    Recommendations to design, description and datastructure

    • Design Your Experiment!

      DESIGN YOUR EXPERIMENT

      We highly recommend to arrange a first consultancy date before you set up your study or experiment to discuss the statistical aspects of experimental design. The prerequisite of any statistical evaluation is the randomized replication of treatments of interest in experimental settings or a proper plan for obtaining random samples in observational studies

    • Describe Your Experiment!

      DESCRIBE YOUR EXPERIMENT

      When you describe your experiment, think of the following five issues:

      1. Experimental units: What is your experimental unit? In a lab experiment, the experimental units might be e.g., single plants, animals, or cell cultures in petri dishes. In a field or greenhouse experiment, they might be e.g., single plants, plots, or entire fields.

      2. Randomization structure: Randomization means that the treatments of interest are repeatedly and randomly assigned to the single experimental units, at least at some level of the experiment. Name your randomization structure unmistakably (“completely randomized”, “split-plot”, “block design”, …) or describe it concisely (a picture or drawing might help you). How have experimental units been arranged in time and space? What sub-structures are involved in that arrangement (e.g., technical replications, sub-sampling, …)?

      3. Response variables: Which variables measure the effect you are interested in? Are they measured in continuous numbers, counts of events or individuals, percentages/proportions, ratios of two primary variables, …?

      4. Explanatory variables: Which variables or factors are supposed to explain differences in the response variables? How many factor levels are there? Which factors/variables are of primary interest?

      5. Experimental question: Explain the purpose of your research as precisely as possible. If you're not quite sure about the experimental question of interest, talk to your supervisor first! “I want to find out if increasing N fertilization has an impact on the leaf area”, is a sensible research goal. “I want to find significant p-values”, is not.

    • Tidy Up Your Data!

      TIDY UP YOUR DATA!

      • If possible, submit your data as txt or csv file. Excel-type xls files can be accepted as well.
      • Data that should be analyzed together should (normally) be in one single file (if you provide an xls file: in one single sheet; exception, e.g., high dimensional data).
      • Record your data in flat file format: there should be one separate line for each experimental unit (plant, animal, pot, petri dish, …) in your data table i.e., all information regarding a certain experimental unit should be in one row. The columns should contain the values of observed variables and controlled factors as well as information in which partial experiment or randomization structure (e.g., in which block) the particular experimental units were placed (exception: highdimensional data).
      • All columns should have (short) headers. They may contain letters and numbers but no special characters (ä ß µ % $), mathematical operators (+ - * / ^), brackets, or blanks. Underscores are okay.
      • Code missing values by “NA” and not by numerical values like 0 or 999.
      • Denote all structures in the experiment which might influence the outcome by introducing a new variable (i.e., a new column), even if these variables are not of direct interest (e.g., if parts of the experiment were performed in different weeks, introduce a new column that codes which observation comes from which week).
      • If you submit an xls file, your data sheet for statistical analysis should not contain:
        • formulas, calculations or graphs
        • comments and explanations
        • blank lines, empty columns or empty cells within the table
        • colors, fonts, boldface, etc. as the only distinction of treatments or replications
        • links to other documents
        • several tables in one sheet
    • Example dataset in flat file format

      (KOPIE 5)

      [Translate to English:] Ein Datensatz im flat file format, bei dem alles eindeutig deklariert ist, könnte so aussehen:

      Jahr

      Ort

      Duenger

      Gewicht

      Blattflaeche

      Qualitaet

      2012

      Ruthe

      A

      22.43

      117.4

      2

      2012

      Ruthe

      B

      25.91

      129.3

      3

      2012

      Ruthe

      C

      26.11

      NA

      2

      2012

      Ruthe

      D

      29.98

      138.5

      1

      2012

      Hannover

      A

      23.57

      120.1

      3

      2012

      Hannover

      B

      26.92

      125.6

      3

      2013

      Ruthe

      A

      21.88

      118.2

      2

      2013

      Ruthe

      B

      23.56

      123.3

      3