it doesn't matter what you do, but it does matter who does it!

14
It doesn't matter what you do, but it does matter who does it! Martin Shepperd, Brunel U Tracy Hall, Brunel U David Bowes, U. of Hertfordshire 1

Upload: giza

Post on 23-Feb-2016

56 views

Category:

Documents


0 download

DESCRIPTION

It doesn't matter what you do, but it does matter who does it!. Martin Shepperd, Brunel U Tracy Hall, Brunel U David Bowes, U. of Hertfordshire. Overview. Many empirical studies (200+) to predict software faults No technique dominates - PowerPoint PPT Presentation

TRANSCRIPT

Page 1: It doesn't matter what you do, but it does matter who does it!

1

It doesn't matter what you do, but it does matter who does it!

Martin Shepperd, Brunel UTracy Hall, Brunel U

David Bowes, U. of Hertfordshire

Page 2: It doesn't matter what you do, but it does matter who does it!

2

Overview

• Many empirical studies (200+) to predict software faults

• No technique dominates• Conduct a meta-analysis to explain variation in

the results• Used factors of (i) classifier (ii) metric type (iii)

data set (iv) research group

Page 3: It doesn't matter what you do, but it does matter who does it!

3

Systematic Review

• Conducted by Tracy Hall and David Bowes– T. Hall, S. Beecham, D. Bowes, D. Gray, and S. Counsell. “A systematic

literature review on fault prediction performance in software engineering”, Accepted for publication in TSE (download from BURA).

• Located 208 relevant primary studies• Due to reporting requirements used 18

studies that contain 194 results– binary classifiers, confusion matrix, context details

Page 4: It doesn't matter what you do, but it does matter who does it!

4

(i) Classifier

Page 5: It doesn't matter what you do, but it does matter who does it!

5

(ii) Metric Type

• Delta• Static• Process• Other• Combinations

Page 6: It doesn't matter what you do, but it does matter who does it!

6

(iii) Data Set

ECLIP :93EMTEL :26MOZ :25COS :16EXCL : 9VISTA : 4(Other):21

Page 7: It doesn't matter what you do, but it does matter who does it!

7

(iv) Research Group

Page 8: It doesn't matter what you do, but it does matter who does it!

8

Response variable

Response variable – Matthews correlation coefficient (MCC)• stable (uses all 4 cells of the confusion matrix)• easy to interpret (0=random)• easy to compare• related to chi-squared test

Page 9: It doesn't matter what you do, but it does matter who does it!

9

Matthews correlation coefficient

Page 10: It doesn't matter what you do, but it does matter who does it!

10

ANOVA model4-way linear random effects model with

interactions

Page 11: It doesn't matter what you do, but it does matter who does it!

11

ANOVA Results

Factor % of varAuthor group 61%Metric family 3%Author/metric 9%Everything else 8% (but not significant)Residuals 19%

Page 12: It doesn't matter what you do, but it does matter who does it!

12

Confounders?• autocorrelation• system age• pre /post-release data collection

not significant• Homogeneity of variances

robust Levene test p=0.51• Normality of the RV

slight +ve skew (0.12) and leptokurtosis (0.26)

Page 13: It doesn't matter what you do, but it does matter who does it!

13

Conclusions

• There are problems with how research is replicated– expertise– bias

• Search to– de-skill– de-bias

Page 14: It doesn't matter what you do, but it does matter who does it!

14

Final word

We cannot ignore the fact that the main determinant of a validation study result is which research group undertakes it.